WO2014188385A2

WO2014188385A2 - A process for bromination of arylene dianhydrides and a method of synthesis of diimides thereof

Info

Publication number: WO2014188385A2
Application number: PCT/IB2014/061657
Authority: WO
Inventors: Thimmaiah Govindaraju; Yelisetty VENKATA SUSEELA
Original assignee: Jawaharlal Nehru Centre For Advanced Scientific Research
Priority date: 2013-05-23
Filing date: 2014-05-23
Publication date: 2014-11-27
Also published as: WO2014188385A3

Abstract

The present disclosure relates to a process for bromination of arylene dianhydrides, particularly1,4,5,8-naphthalenetetracarboxylic dianhydride (NDA) using 5,5-dimethyl-1,3- dibromohydantoin (DBH) or tribromoisocyanuric acid (TBCA) as brominating agent. The disclosure further relates to condensation of the brominated dianhydrides with amines to yield corresponding imides, particularly naphthalene diimides (NDI) which are versatile precursors for the synthesis of core functionalized naphthalene diimides. The present disclosure further relates to the use of DBH or TBCA as brominating agents for brominating arylene dianhydride, particularly naphthalene tetracarboxylic dianhydride.

Description

A PROCESS FOR BROMINATION OF ARYLENE DI ANHYDRIDE S AND A METHOD OF SYNTHESIS OF DIIMIDES THEREOF"

TECHNICAL FIELD

The present disclosure relates to the field of organic/synthetic chemistry. Specifically, the disclosure relates to a process for bromination of arylene dianhydrides, particularly 1,4,5,8- naphthalenetetracarboxylic dianhydride ( DA) using 5,5-dimethyl-l,3-dibromohydantoin (DBH) and tribromoisocyanuric acid (TBCA) as brominating agents. The disclosure further relates to condensation of the brominated dianhydrides with amines to yield corresponding imides, particularly naphthalene diimides (NOT) which are versatile precursors for the synthesis of core functionalized naphthalene diimides.

The present disclosure relates to a method of synthesis of naphthalene diimides using naphthalene dianhydrides as starting material which are brominated with the brominating agents such as DBH or TBCA followed by condensing the resulting brominated dianhydrides with amines to yield respective diimides which may be a substituted imide or core function imide.

The present disclosure further relates to the use of DBH or TBCA as brominating agents for brominating arylene dianhydride, particularly NDA.

BACKGROUND OF THE DISCLOSURE

The classical methods reported in literature for the synthesis of brominated compounds of NDA involves (i) molecular bromine as a brominating agent in presence of catalytic amount of iodine either in oleum or mixture of cone. H₂SO₄ and oleum as a solvent, (ii) dibromoisocyanuric acid (DBI) as a source of bromine in oleum, (iii) use of sodium bromide (NaBr) as a brominating agent in oleum. However, most of these methods suffer from several drawbacks such as the reaction involving molecular bromine could not be reproduced in high yield. Moreover, bromine is a hazardous and corrosive reagent which is difficult to handle due to its toxicity and high vapour pressure. Prolonged reaction time and high temperature are required to carry out the reaction (i.e. the tetrabromo-NDA was synthesized at 140 °C for 4 weeks). The dibromoisocyanuric acid (DBI) is expensive and not readily available in large quantity. In NaBr method, special equipment and harsh reaction conditions were required to carry out the reaction. Most importantly, after the bromination, convenient procedure for the isolation and purification of brominated NDAs is not available and instead compounds were purified and characterized by converting into corresponding core substituted NDIs.

Therefore despite the availability of the methods described above, high demand for bromo- NDAs in the preparation of core substituted NDIs warrants the need for newer efficient and convenient methodology for the rapid and region selective bromination of NDA.

The present disclosure aims at overcoming the aforementioned drawbacks by disclosing simple, economical, practical and industrially viable reagents and methodology for the preparation of NDAs. The bromo NDAs subsequently serve as direct precursors for the synthesis of core functionalized NDIs.

STATEMENT OF DISCLOSURE

Accordingly, the present disclosure relates to a process for bromination of arylene dianhydride to obtain brominated arylene dianhydride, said process comprising act of brominating arylene dianhydride with brominating agent selected from 5,5-dimethyl-l,3- dibromohydantoin (DBH) and tribromoisocyanuric acid (TBCA) to obtain brominated arylene dianhydride; a one step process for condensation of brominated arylene dianhydride to obtain arylene diimide, said process comprising act of reacting brominated arylene dianhydride with amine to obtain arylene diimide; a process for obtaining imide and core substituted arylene diimide from arylene dianhydride, said process comprising acts of: (a) obtaining brominated arylene dianhydride from arylene dianhydride by the process described above, (b) reacting the brominated arylene dianhydride with amine to obtain imide substituted arylene diimide, and (c) reacting the imide substituted arylene diimide with amine to obtain imide and core substituted arylene diimide; a process for obtaining imide and core substituted arylene diimide from arylene dianhydride, said process comprising acts of: (a) obtaining brominated arylene dianhydride from arylene dianhydride by the process as described above, and (b) reacting the brominated arylene dianhydride with amine to obtain imide and core substituted arylene diimide; use of 5,5-dimethyl-l,3-dibromohydantoin as brominating agent for brominating arylene dianhydrides; and use of tribromoisocyanuric acid as brominating agent for brominating arylene dianhydride BRIEF DESCRIPTION OF ACCOMPANYING FIGURES

In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:

Figure 1 shows the chemical structure of DBH and bromination of DA to bromo- DAs 1-3 using DBH as highly efficient brominating reagent

Figure 2 shows the preparation of selectively N,N'-bis(«-octyl)-substituted mono-, di- and tetra-bromo NDIs .

Figure 3a shows the core substitution of bromo-NDIs (4, 5 and 7) with «-octylamine (n- C₈HivNH₂).

Figure 3b shows the one-step synthesis of core substituted NDIs 8, 9 and 10 with n- octylamine.

Figure 4 shows photographs of thin layer chromatography (TLC) profiles of core substituted NDIs 8, 9 and 10 under a) visible (day) light and b) UV light.

Figure 5 shows UV-vis absorption spectra of core-unsubstituted bromo-NDIs 4, 5 and 7 in chloroform.

Figure 6 shows (a) UV-vis absorption spectra of core substituted NDIs 8, 9 and 10 in chloroform, b) Photographs of solutions of NDIs 8, 9 and 10 in chloroform showing bright visible (red, blue and green respectively) colors under day light, c) Emission spectra of NDIs 8, 9 and 10 respectively ( ^_χ = 497, 577 and 597 nm respectively), d) Photographs of solutions of NDIs 8-10 in chloroform showing bright fluorescence emission under UV-light (Excitation wavelength of 365 nm is employed for NDIs 8-10). Figure 7 shows the chemical structure of TBC A and the bromination of NDA to mono-, di- and tetrabromo- NDAs using TBCA as highly efficient brominating reagent.

Figure 8a shows the one-step reaction for core substitution of bromo-NDAs (1, 2 and 3) with «-butylamine (/7-C₄H₉NH₂).

Figure 8b and 8c show the two-step method for the synthesis of core substitured NDIs 11, 12, and 13 using «-butylamine.

Figure 9 shows a) UV-vis absorption spectra of core substituted NDIs 11, 12 and 13 in chloroform, b) Normalized Emission spectra of NDIs 11, 12 and 13 respectively (λ_εχ = 497, 577 and 600 nm respectively), c) Photographs of solutions of NDIs 11, 12 and 13 in chloroform showing bright visible (red, blue and green respectively) colors under day light, d) Photographs of solutions of NDIs 11-13 in chloroform showing bright fluorescence emission under UV-light (Excitation wavelength of 365 nm is employed for NDIs 11-13).

Figure 10 illustrates the photophysical properties of bromo substituted NDA. Figure 10(a) shows UV-vis absorption spectra of brominated NDA compounds 1, 2 and 3. Figure 10(b) shows photographs of solutions of NDA 1, 2 and 3 in DMSO and NDI 4, 5 and 7 in chloroform, (colorless or show faint yellow color under day light).

Figure 11 illustrates the photophysical properties of bromo substituted NDA. Figure 11(a) shows UV-vis absorption spectra of brominated NDA compounds 1, 2 and 3. Figure 11(b) shows the photographs of solutions of NDA 1, 2 and 3 in DMSO (colorless or show faint yellow color under day light).

Figures 12- 20 show the 1H and ¹³C NMR Spectra of compounds 1, 2, 3, 4, 5, 7, 8, 9 and 10 respectively.

Figure 21 shows the mass spectrum of compound 4(Calculated [M+H]⁺ = 569.2015) Figure 22 shows the mass spectrum of compound 5(Calculated [M+H]⁺ = 649.1100) Figure 23 shows the mass spectrum of compound 7(Calculated [M+H]⁺ = 806.9289) Figure 24 shows the mass spectrum of compound 8(Calculated [M+H]⁺ = 618.4271) Figure 25 shows the mass spectrum of compound 9 (Calculated [M+H]⁺ = 745.5632) Figure 26 shows the mass spectrum of compound 10(Calculated [M+H]⁺ = 999.8354) Figure 27 shows the 1H and ¹³C NMR Spectrum of compound 11. Figure 28 shows the 1H and ¹³C NMR Spectrum of compound 12. Figure 29 shows the 1H and ¹³C NMR Spectrum of compound 13. Figure 30 shows the mass spectrum of compound 11 (Calculated [M+H]⁺ = 450.2393). Figure 31 shows the mass spectrum of compound 12 (Calculated [M+H]⁺ = 521.3128). Figure 32 shows the mass spectrum of compound 13 (Calculated [M+H]⁺ = 663.4598). DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to a process for bromination of arylene dianhydride to obtain brominated arylene dianhydride, said process comprising act of brominating arylene dianhydride with brominating agent selected from 5,5-dimethyl-l,3-dibromohydantoin (DBH) and tribromoisocyanuric acid (TBCA) to obtain brominated arylene dianhydride.

In an embodiment of the present disclosure, the brominated arylene dianhydride is precipitated and recrystallized to obtain pure brominated arylene dianhydride. .

In another embodiment of the present disclosure, the arylene dianhydride is 1,4,5,8- naphthal enetetracarb oxy li c di anhy dri de .

In yet another embodiment of the present disclosure, the arylene dianhyride is dissolved in concentrated acid prior to bromination. In still another embodiment of the present disclosure, the concentrated acid is selected from a group comprising sulphuric acid, oleum and vitriolic acid.

In still another embodiment of the present disclosure, the brominating agent and arylene dianhydride are in a ratio ranging from about 0.5 : 1 to 3 : 1.

In still another embodiment of the present disclosure, the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride, 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride and 2,3,6,7-Tetrabromo- 1,4,5, 8-naphthalenetetracarboxylic dianhydride.

In still another embodiment of the present disclosure, the bromination is carried out at a temperature ranging from about 0 °C to about 80 °C for a time period ranging from about 1 hour to about 16 hours.

The present disclosure relates to a one step process for condensation of brominated arylene dianhydride to obtain arylene diimide, said process comprising act of reacting brominated arylene dianhydride with amine to obtain arylene diimide.

In an embodiment of the present disclosure, the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5, 8-naphthalenetetracarboxylic dianhydride, 2,6- Dibromo-1,4,5, 8-naphthalenetetracarboxylic dianhydride and 2,3,6,7-Tetrabromo-l,4,5,8- naphthal enetetracarb oxy li c di anhy dri de .

In another embodiment of the present disclosure, the amine is selected from a group comprising n-octylamine , n-butylamine.

In yet another embodiment of the present disclosure, the process is carried in presence of reagent selected from group comprising dichloromethane, hexane and combination thereof.

In still another embodiment of the present disclosure, the arylene diimide is selected from a group comprising N,N'-Bis-(«-octyl)-2-(«-octylamino)-l, 4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,6-di(«-octylamino)-l,4,5,8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,3,6,7-tetra(«-octylamino)-l,4,5,8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2-(«-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«- butyl)-2,6-di(«-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide and N,N'-Bis-(«- butyl)-2,3,6,7-tetra(«-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide.

In still another embodiment of the present disclosure, the condensation is carried out at a temperature ranging from about 0 °C to about 100 °C for a time period ranging from aboutl hour to about 30 hours.

In still another embodiment of the present disclosure, wherein the amine and the brominated arylene dianhydride is at a ratio of about 3 : 1.

In still another embodiment of the present disclosure, the arylene diimide is purified to obtain purified arylene diimide.

In still another embodiment of the present disclosure, the purification is carried out by a process selected from a group comprising chromatography, recrystallization, precipitation and combination thereof.

The present disclosure relates to a process for obtaining imide and core substituted arylene diimide from arylene dianhydride, said process comprising acts of:

(a) obtaining brominated arylene dianhydride from arylene dianhydride as described above;

(b) reacting the brominated arylene dianhydride with amine to obtain imide substituted arylene diimide;

(c) reacting the imide substituted arylene diimide with amine to obtain imide and core substituted arylene diimide.

In still another embodiment of the present disclosure, the arylene dianhydride is 1,4,5,8- naphthal enetetracarb oxy li c di anhy dri de . In still another embodiment of the present disclosure,the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride, 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride and 2,3,6,7-Tetrabromo- 1,4,5, 8-naphthalenetetracarboxylic dianhydride.

In still another embodiment of the present disclosure, the amine is selected from comprising n-octylamine and n-butylamine

In still another embodiment of the present disclosure, the steps (b) and (c) are carried in presence of reagent selected from a group comprising acetic acid, formic acid, methanol, phosphorus tribromide, toluene, water, sodium sulphate, dimethyl formamide, dichloromethane, hexane and combination thereof.

In still another embodiment of the present disclosure, the amine and the brominated arylene dianhydride is at a ratio of about 3 : 1.

In still another embodiment of the present disclosure, the imide substituted arylene diimide is selected from a group comprising N,N'-Bis(«-octyl)-2-bromo-l, 4,5,8- naphthal enetetracarb oxy li c diimide, N,N'-Bis(«-octyl)-2,6-dibromo-l,4,5,8- naphthal enetetracarb oxy li c diimide, N,N'-Bis(«-octyl)-2,3,6,7-tetrabromo-l,4,5,8- naphthal enetetracarb oxy li c diimide, N,N'-Bis(«-butyl)-2-bromo-l,4,5,8- naphthal enetetracarb oxy li c diimide, N,N'-Bis(«-butyl)-2,6-dibromo-l,4,5,8- naphthalenetetracarboxylic diimide and N,N'-Bis(«-butyl)-2,3,6,7-dibromo-l,4,5,8- naphthal enetetracarb oxy li c diimi de .

In still another embodiment of the present disclosure, the amine and imide substituted arylene dianhydride is at a ratio ranging from about 1 : 1 to about 5: 1.

In still another embodiment of the present disclosure, the imide and core substituted arylene diimide is selected from a group comprising N,N'-Bis-(«-octyl)-2-(«-octylamino)-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,6-di(«-octylamino)-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,3,6,7-tetra(«-octylamino)-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2-(«-butylamino)-l,4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2,6-di(«-butylamino)-l,4,5,8- naphthalenetetracarboxylic diimide and N,N'-Bis-(«-butyl)-2,3,6,7-tetra(«-butylamino)- 1,4,5,8 -naphthal enetetracarb oxy li c diimi de .

(a) obtaining brominated arylene dianhydride from arylene dianhydride by the process as described above;

(b) reacting the brominated arylene dianhydride with amine to obtain imide and core substituted arylene diimide.

In an embodiment of the present disclosure, the arylene dianhydride is 1,4,5,8- naphthal enetetracarb oxy li c di anhy dri de .

In another embodiment of the present disclosure, the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride, 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride and 2,3,6,7-Tetrabromo- 1,4,5, 8-naphthalenetetracarboxylic dianhydride.

In yet another embodiment of the present disclosure, the amine is selected from a group comprising n-octylamine and n-butylamine.

In still another embodiment of the present disclosure, the step (b) is carried in presence of reagent selected from a group comprising dichloromethane, hexane and combination thereof.

In still another embodiment of the present disclosure, the imide and core substituted arylene diimide is selected from a group comprising N,N'-Bis-(«-butyl)-2-(«-butylamino)-l,4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2,6-di(«-butylamino)-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2,3,6,7-tetra(«-butylamino)-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2-(«-octylamino)-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,6-di(«-octylamino)-l, 4,5,8- naphthalenetetracarboxylic diimide and N,N'-Bis-(«-butyl)-2,3,6,7-tetra(«-butylamino)- 1,4,5, 8-naphthalenetetracarboxylic diimide . The present disclosure relates to the use of 5,5-dimethyl-l,3-dibromohydantoin as brominating agent for brominating arylene dianhydrides.

The present disclosure relates to the use of tribromoisocyanuric acid as brominating agent for brominating arylene dianhydride.

In an embodiment of the present disclosure, the arylene dianhydride is naphthalene dianhydride.

The present disclosure relates to a process for bromination of arylene dianhydrides using one of 5,5-dimethyl-l,3-dibromohydantoin (DBH) and tribromoisocyanuric acid (TBCA) as brominating agents. The disclosure further relates to condensation of the brominated dianhydrides obtained with amines to yield corresponding imides, particularly naphthalene diimides ( DI) which are versatile precursors for the synthesis of core functionalized naphthalene diimides.

In another embodiment, the present disclosure relates to a process of synthesis of naphthalene diimides using naphthalene dianhydrides as starting material which are brominated with brominating agents such as DBH or TBCA followed by condensing the resulting brominated dianhydrides with amines to yield respective diimides which may be a substituted imide or core function imide.

In another embodiment, the present disclosure relates to use of DBH and TBCA as brominating agents. In an embodiment of the present disclosure, the present disclosure relates to use of DBH and TBCA for bromination of arylene dianhydrides, particularly naphthalene tetracarboxylic dianhydride. However, it is to be understood that the use of DBH and TBCA are not only restricted to bromination of arylene dianhydrides, but also for brominating any aromatic or unsaturated compounds selected from group comprising but not limited to anthracene, naphthalene, pyrene, phenanthrene, acenaphthene, nitrobenzene and trifluorob enzene .

In another embodiment, the present disclosure relates to a process of bromination of 1,4,5,8- naphthalenetetracarboxylic dianhydride (NDA) by using efficient and economical brominating reagents namely 5,5-dimethyl-l,3-dibromohydantoin (DBH) and tribromoisocyanuric acid (TBCA). Mono-, di- and tetra-brominated products are obtained in good to excellent yield by varying the equivalent of brominating reagent to the NDA as a result of which the products obtained are purified by simple crystallization method without the need for any further purification methods. Varying the equivalent amounts of brominating reagent to NDA enables the synthesis of pure bromo compounds which are further purified by using simple crystallization method and then these pure bromo compounds are subjected to further condensation reactions. Whereas in literature, mixture of brominated compounds were subjected to imidation and further purified to yield various core-substituted products.

The present disclosure further relates to condensation of the mono- di- and tetra- brominated dianhydrides with amine to yield the corresponding imide (N P) substituted mono-, di- and tetrabromo-naphthalene diimides which are versatile precursors for the synthesis of the core functionalized naphthalene diimides, wherein the amine is selected from a group comprising n-octylamine and n-butylamine.

In an embodiment of the present disclosure, Naphthalene diimides (NDIs) are a class of aromatic molecules which play an important role in biomedicine, organic electronics and materials science attributed to their remarkable electronic, spectroscopic and self-assembly properties. NDIs have been extensively used in supramolecular chemistry, electron-transfer systems, DNA intercalation and sensing, host-guest systems, synthetic ion channels, electrically conductive aggregates, «-type organic field effect transistors (OFETs), redox processes, and synthetic photosy stems. Structurally NDIs are of two categories: (i) imide- substituted and (ii) imide- and core substituted derivatives. Two different methods are used to prepare NDIs, (i) by introducing N,N" -imide substituent groups, and (ii) functionalizing the naphthalene core. The imide substituted NDIs are prepared by the simple condensation of 1,4,5, 8-naphthalenetetracarboxylic dianhydride (NDA) with suitable amine groups. The imide (N,N-) substituents of NDIs generally have minimal influence on optical and electronic properties, although they can be used to control solubility, aggregation, and intermolecular packing in the solid state. On the other hand, the naphthalene core substitution in NDIs significantly alters their electrical, optical and redox properties.NDIs bearing electron donating core substituents have been shown to exhibit a range of fluorescent colors and the phenomenon is popularly known as rainbow fluorescence, that has found extensive applications in single molecule fluorescence technique and organic solar cells.

In an embodiment of the present disclosure, DBH is a stable solid, readily available, widely used as a disinfectant for drinking water purification, recreational water treatment, as a bleaching agent in pulp and paper mills, and for treating industrial/commercial water cooling systems. DBH is a highly promising alternative brominating reagent for NDA due to its high efficiency, mild reaction conditions and low cost. Moreover, the methodology or the process of the present disclosure avoids the handling of molecular bromine.

In an embodiment, the present disclosure provides a process for region selective bromination, product purification and characterization of 2-bromo, 2, 6-dibromo and 2,3,6,7-tetrabromo- NDAs using DBH in 98% H₂SO₄ under ambient conditions.

In an embodiment, the present disclosure also provides a process for the bromination of NDA using TBCA as a brominating agent.

In an embodiment of the present disclosure, TBCA is a white solid which is a less toxic and safe brominating reagent that can be easily synthesized in bulk from isocyanuric acid and NaBr in the presence of Oxone. Further, TBCA is particularly advantageous because of high atom-economy as it is capable of transferring three Br+ to one substrate which accelerates the rate of reaction compared to any currently used brominating reagents including dibromoisocyanuric acid (DBI). Easy and straight forward synthesis of TBCA reagent in large quantity makes it an industrially viable reagent for the bromination of NDA while DBI is highly expensive and not readily available in bulk quantity. The bromination reactions of NDA using TBCA are fast, require low equivalents of TBCA and is performed under milder conditions compared to any other brominating reagent reported in the literature. Mono-, di- and tetra-bromination of NDA core are performed at ambient conditions by varying equivalent amount of TBCA.

In an embodiment of the present disclosure, the reaction time of tetra-bromination of NDA is greatly reduced by heating the reaction mixture towards the end. Thus TBCA is an efficient, economical, industrially viable and eco-friendly reagent for the region selective bromination of NDA core. Further, the present disclosure demonstrates the utility of bromo-ND As for the preparation of imide and core functionalized NDIs and reports the photophysical properties of imide and core substituted NDIs (Figure 10) to show the effect of substitutions on their optical properties.

In an embodiment of the present disclosure, the mono-, di- and tetrabromo-NDAs are prepared as shown in Figure 1. NDA is treated with an amount of DBH equivalent to about 0.55 times the amount of NDA(0.55 equiv) in about 98% H₂S0₄ at about 0 °C to about 25 °C for about 12 h in a stoppered round flask (100 mL). The reaction affords a crude product consisting of mainly 2-bromo-NDA (1), trace of dibromo-NDA (2) and unreacted starting material. The crude product is recrystallized from dimethylformamide to obtain (1) in about 70% yield (Figure 1). Reaction of NDA and an amount of DBH equivalent to about 1.5 times the amount of NDA (1.5 equivalent) in about 98% H₂S0₄ at about 50 °C for about 10 h gives crude product 2,6-dibromo-NDA (2) along with a small amount of partially ring opened side product. The partially ring opened side product is selectively recrystallized from dimethylformamide solution. The supernatant is precipitated by adding water to obtain pure 2,6-dibromo-NDA (2) in about 82% yield. Furthermore, the integrity of the product is confirmed by converting 2,6-dibromo-NDA (2) into corresponding imide substituted product N,N'-bis(«-octyl)-2,6-dibromo-NDI (5). Tetrabromination of NDA is carried out in about 98%) sulfuric acid with an amount of DBH equivalent to about 3 times the amount of NDA (3 equivalents) at about 0 °C to about 25 °C for about 4 h and at about 80 °C for about 12 h to give 2,3,6,7-tetrabromo-NDA (3) in about 96% yield. The 1H NMR spectrum (DMSO-d₆) does not show any proton resonance, indicating the absence of mono- and di-brominated compounds in the product (Figure 14). Additional confirmation for the tetrabromo-NDA (3) is obtained by converting it into alkyl substituted product, i.e. the purity of tetrabromo-NDA (3) is confirmed by selective imidation using «-octyl amine which gives pure tetra bromo NDI (7).

In an embodiment, the present disclosure also relates to the use of a highly efficient and cost- effective reagent namely tribromoisocyanuric acid, for the bromination of 1,4,5,8- naphthalenetetracarboxylic dianhydride (NDA) under moderate reaction conditions. Bromination of NDA using tribromoisocyanuric acid (TBCA) in concentrated H₂SO₄ as a solvent is fast and effective. NDA is brominated smoothly under optimized reaction conditions to give mono-, di- and tetra-brominated products in good to excellent yields using TBCA. The brominated NDA products are easily purified by recrystallization method. Simple one step preparation of brominating reagent TBCA, its high atom economy, mild reaction conditions and simple workup procedure make this bromination method a feasible and preferable route for the synthesis of mono-, di- and tetra-brominated 1,4,5, 8-NDAs. Atom economy is more in case of TBCA when compared to DBI (Dibromoisocyanuric acid) in terms of bromine atom donation as TBCA can donate three atoms when compared to two atoms donated by DBI. These bromo-NDAs are used as precursors for the synthesis of N- imide and core functionalized 1,4,5,8-napthalenetetracarxylic diimides (NDIs) by treating with «-butylamine to yield corresponding functionalized mono-, di- and tetra-(«-butylamino)- naphthalene diimides in good yields in single step reaction compared to two-step process reported in the literature.

The mono-, di- and tetrabromo-NDAs with TBCA are prepared as shown in Figure 7. The reaction conditions are optimized by varying the equivalents of TBCA, reaction temperature and time as shown in Table 3. NDA is treated with an amount of TBCA equivalent to about 0.5 times the amount of NDA (i.e. about 0.5 equiv) in about 98% H₂SO₄ at about 0 °C to about 25 °C for about 12 h in a stoppered round flask (100 mL). The reaction affords a crude product consisting of mainly 2-bromo-NDA (1), trace of dibromo-NDA (2) and unreacted starting material. The crude product is recrystallized in dimethylformamide to obtain (1) in about 70%) yield (Figure 7). Reaction of NDA and an amount of TBCA equivalent to about 1 time the amount of NDA (1 equivalent) of TBCA in about 98%> H₂SO₄ at about 0 °C to about 25 °C for about 18 h gives a crude product which is further recrystallized in dimethylformamide to obtain 2,6-dibromo-NDA (2) in about 76% yield. The integrity of the product is further confirmed by converting 2,6-dibromo-NDA (2) into corresponding Ν,Ν'- Bis-(n-butyl)-2,6-di(n-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide (5). Tetrabromination of NDA is carried out in about 98%> sulfuric acid with about 2.5 equivalents of TBCA at about 0 °C to about 25 °C, preferably about 24 °C , for about 24 h or at about 50 °C to about 80 °C, for about 3 to about 8 hours, preferably at about 80 °C for about 8 hours to give 2, 3, 6, 7-tetrabromo-NDA (3) in about 94% yield. The 1H NMR spectrum (DMSO-d6) does not show any proton resonance, indicating the absence of mono- and di-brominated compounds in the product (Figure 14). Additional confirmation for the tetrabromo-NDA 3 is obtained by converting it into core substituted product.

The process of bromination using DBH/TBCA is broadly carried out at a temperature ranging from about 0 °C to about 80 °C for a time period ranging from about 1 hour to about 16 hours.

Table 3: Optimized reaction conditions for bromination of NDA using TBCA as a reagent

In an embodiment of the present disclosure, Imide-substituted NDIs play a major role in controlling solubility, aggregation, and intermolecular packing in the solid state. Such molecular organizations indirectly influence various properties of NDIs. Imide-substituted NDIs in the present disclosure are obtained by treating the bromo-NDA's with amine. For example: The selective Ν,Ν'-imidation of bromo-NDAs (1-3) is outlined in Figure 2 and Figure 8b, 8c. The NJf - bis(«-octyl)-2-bromo-NDI (4) and N,N'-bis(«-butyl)-2-bromo-NDI (a) are synthesized by treating (1) with an amount of «-octylamine («-C8H₁₇NH₂) or n- butylamine («-C₄H₉NH₂)equivalent to about 3 times the amount of compound (1) (i.e.3 equivalents) in acetic acid at about 80-90 °C for about 3 h.

Imidation is performed in acetic acid mainly to avoid nucleophilic aromatic substitution reactions. In highly protic solvent like acetic acid, most amino functions are protonated, the reactivity of amine is sufficiently low and therefore avoids core substitution. Alternatively, formic acid may be used which also serves as a good protic solvent and avoids core substitution. After completion of the reaction, reaction mixture is filtered and washed with methanol to afford pure product N,A^-bis(«-octyl)-2-bromo-NDI (4) or in about 80% yield without requiring any further purification on column chromatography. Similarly, N,jV-bis(«-octyl)- 2,6-dibromo DI (5) is synthesized by reacting 2,6-dibromo DA (2) with an amount of n- octylamine equivalent to about 3 times the amount of compound (2) (i.e. 3 equivalents) in acetic acid at about 90 °C for about 4 h in about 75% yield. For the imidation of tetrabromo- NDA (3), the procedure reported by Wiirthner and coworkers is followed. Imidation of 2,3,6,7-tetrabromo-NDA (3) with an amount of «-octylamine equivalent to about 3 times the amount of compound (3) (i.e. 3 equivalents) in glacial acetic acid at about 130 °C for about 6 h gives the desired N,A^-bis(«-octyl)-tetrabromo-NDI (7) in >10% yield, along with ring opened 2,3,6,7-tetrabromo-4,8-bis(«-octylcarbamoyl)naphthalene-l,5-dicarboxylic acid (6) as a major product and trace of core substituted products. In order to overcome this difficulty in synthesizing exclusively (7) in good yield, two step synthesis reported by Liu and coworker is followed. Accordingly, tetrabromo-NDA (3) is reacted with an amount of «-octylamine equivalent to about 3 times the amount of compound (3) (i.e. 3 equivalents) in glacial acetic acid at about 120 °C for about 30 min to obtain uncyclized 2,3,6,7-tetrabromo-4,8-bis(«- octylcarbamoyl) naphthalene- 1,5-dicarboxylic acid, which is further treated with PBr₃ in toluene at reflux for about 6 h to yield N,A^-bis(«-octyl)-tetrabromo-NDI 7 in about 60% overall yield calculated from tetrabromo-NDA(3).

Similarly, N,N'-Bis(«-butyl)-2-bromo-l,4,5,8-naphthalenetetracarboxylic diimide (a) is synthesized by reacting 2, bromo NDA 1 with n-butylamine (3 : 1) in the presence of acetic acid at 80- 90°C . N,N'-Bis(«-butyl)-2,6-dibromo-l,4,5,8-naphthalenetetracarboxylic diimide is synthesized by reacting 2, 6 di bromo NDA 2 with n- butylamine (3 : 1) in acetic acid at 90 °C for about 4 hours. N,N'-Bis(«-butyl)-2,3,6,7-dibromo-l,4,5,8-naphthalenetetracarboxylic diimide is synthesized by reacting tetrabromo NDA 3 with n-butylamine (3 : 1) in acetic acid at 120 °C for 30 minutes.

Core functionalization of N,iV-bis(«-octyl)-bromo-NDIs and N,N'-bis(n-butyl)-bromo- NDIs

Core substitutions are particularly important in modulating electronic, optical and redox properties of NDIs. To demonstrate the subsequent utility of the brominating agents (DBH), core substitution of bromo-NDIs (4, 5 and 7) and ( a, b and c)are carried out with n- octylamine and n-butylamine as outlined in the Figure 3 and Figure 8(b) respectively. Initially, the core substitution of bromo-NDIs with «-octylamine/«-butylamine in DMF at about 130 °C is found to result in a complex mixture and after purification on flash column chromatography affords a product in less than 30% yield. Therefore, in order to improve the yield and minimize the side reactions, core substitution of bromo-NDIs in toluene as a solvent is done. The core substitution is found to occur smoothly to afford good to excellent yields. Reaction of N,A^-bis(«-octyl)-2-bromo-NDI (4) with an amount of «-octylamine equivalent to about 1.25 times the amount of compound (4) (i.e. 1.25 equivalents) in toluene under reflux for about 3 h gives core substituted N,N'-bis(«-octyl)-2-(«-octylamino)-NDI (8) in about 96% yield. Similarly, core substitution of N,N'-bis(«-octyl)-2,6-dibromo-NDI (5) and N,A^-bis(«-octyl)-2,3,6,7-tetrabromo-NDI (7) afford corresponding core substituted Ν,Ν'- bis(«-octyl)-2,6-di(«-octylamino)-NDI (9) and N,N'-bis(«-octyl)-2,3,6,7-tetra-(«- octylamino)-NDI (10) in about 92% and about 98% yields respectively. In toluene, reactions are found to be very clean without forming any side products as shown in the thin layer chromatography (TLC) profile under visible- and UV-light after completion of the reaction (Figure 4). The polarity of solvent system used for TLC are 50%, 30% and 10% CH₂CI₂ in hexane in case of N P-bis(n- octyl)-2-(«-octylamino)-NDI (8), N,jV-bis(«-octyl)-2,6- di(«- octylamino)-NDI (9), and N,N'-bis-(«-octyl)-2,3,6,7-tetra-(«-octylamino)-NDI (10) respectively (Figure 4). The photographs of the TLC profiles on silica coated aluminium plates (Merck silica gel 60 F254) are taken under day (visible) light as well as under UV-light (365 nm). The core substituted NDIs (8, 9 and 10) with variable number of core substituents exhibit red, blue and green colors under day light (Figure 4a) and bright fluorescence colors upon shining the UV light (Figure 4b) on these TLC plates.

Similarly, reaction of N,N'-Bis(«-butyl)-2-bromo-l,4,5,8-naphthalenetetracarboxylic diimide (a) with an amount of «-butylamine equivalent to about 1.5 times the amount of the diimide (i.e. 1.5 equivalents) in toluene under reflux for about 2-6 h gives core substituted N,N'-Bis- («-butyl)-2-(«-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide (11) in about 94% yield. Similarly, core substitution of N,N'-Bis(«-butyl)-2,6-dibromo-l,4,5,8- naphthalenetetracarboxylic diimide (b) and N,N'-Bis(«-butyl)-2,3,6,7-dibromo-l, 4,5,8- naphthalenetetracarboxylic diimide (c) afford corresponding core substituted N,N'-Bis-(«- butyl)-2,6-di(«-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide (12) and N,N'-Bis-(n- butyl)-2,3,6,7-tetra(«-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide (13) in about 95% and about 98% yields respectively.

One- Step Imide and Core substitution of brominated NDAs

Core substitution facilitates tuning optical and electronic properties of NDIs. The utility of the brominating reagents of the present disclosure is clearly demonstrated by carrying out the imide and core substitution of brominated NDAs (1, 2 and 3) with n-butylamine for the first time as outlined in the Figure 8b, 8c. The pure mono, di and tetra-brominated NDAs for core substitution prevent the formation of complex mixture of side products which is a common drawback for naphthalene diimides. The core substituted NDIs (11, 12 and 13) exhibit red, blue and green colors by varying the number of core substituents (n-butylamine). Further, n- octylamine may also be used for imide and core substitution of brominated NDAs (1, 2 and 3) in a one-step reaction (Figure 3b). The reaction involved in the synthesis of NDI 8 in a single step method is by reacting 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride 1 with n-octylamine (as a solvent) at a temperature of about 50 °C to about 100 °C for a duration of about 10 to about 32 hours.

Similarly, NDI 9 is synthesized in a single step method by reacting 2,6-Dibromo-l, 4,5,8- naphthalenetetracarboxylic dianhydride 2 with n-octylamine (as a solvent) at a temperature of about 50 °C to about 100 °C, for a duration of about 10 to about 32 hours. NDI 10 is synthesized in a single step method by reacting 2,3, 6,7-Tetrabromo-l, 4,5,8- naphthalenetetracarboxylic dianhydride 3 with n-octylamine (as a solvent) at a temperature of about 50 °C to about 100 °C, for a duration of about 10 to about 32 hours.

The invention is further illustrated by the following Examples. The following examples are provided for illustrative purposes only and are not intended to limit the scope of the invention.

EXAMPLES

Materials and methods

All the reagents are obtained from Sigma-Aldrich and used as received. Column chromatography is performed over silica gel (100-200 mesh). TLC analyses are performed over aluminum plates coated with Merck silica gel 60 F₂₅₄ and visualization under UV light (254 and 365 nm). The solvents used for spectroscopic studies are of spectroscopic grade from Sigma-Aldrich. IR spectra are recorded on Bruker (FT)-IR 8400 instrument and absorptions are expressed in cm^'■\ 1H MR and ¹³C MR spectra are recorded on a Bruker AV-400 and using DMSO-d₆ and CDC1₃ as solvents. Chemical shifts are given in parts per million (ppm) with respect to the internal standard tetram ethyl silane (TMS), and J values are quoted in Hertz. The following abbreviations are used: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, brs = broad singlet, dd = doublet of doublet, and dt = doublet of triplet. Elemental analysis was recorded on Thermoscientific Flash 2000 organic elemental analyzer. High resolution mass spectra are recorded on UHD accurate mass QTOF LC/MS. UV-vis spectra are recorded on a Perkin Elmer Model Lambda 900 spectrophotometer and 50 μΜ of the samples are analyzed in quartz cuvette of 1 cm path length. Fluorescence spectra are recorded on Perkin Elmer LS 55 Luminescence spectrometer. 50 μΜ of the samples are analyzed in quartz cuvette of 1 cm path length. Fluorescence quantum yields in chloroform are determined by the optically dilute method using rhodamine 6G as a reference (cp_f (ethanol) = 0.95 ± 0.015) and refractive indexes of the solvents as published in the CRC handbook.

EXAMPLE 1:

Preparation of Di methyl di bromo hydantoin (DBH)

DBH is widely available commercially. DBH used in the present disclosure is also a commercial DBH. Nonetheless, DBH is easy to prepare and hence DBH prepared by conventional methods can also be used in the present disclosure.

DBH may also be prepared by brominating 5,5- dimethyl hydantoin in the presence of molecular bromine.

EXAMPLE 2:

Preparation of Tribromoisocyanuric acid (TBCA)

In a single neck round bottom (RB) flask, cyanuric aid (about 1.29 g, about 10 mmol) and NaOH (about 1.2 g, about 30 mmol) are taken in about 180 mL H₂0 to which Na₂C0₃ (about 1.58 g, about 15 mmol) and KBr (about 3.57 g, about 30 mmol) are added. The resulting mixture is stirred for about 30 min at about 0 °C to about 25 °C and kept in ice bath and a solution of Oxone^® (about 18.44 g, about 30 mmol) in H₂0 (about 150 mL) is added dropwise over period of about 1 h. A white solid precipitates during the addition of oxidant solution, forming a dense suspension, which is stirred for about 12 h. The product is isolated by vacuum filtration, washed with cold H₂0 and dried under vacuo overnight needing no further purification. Yield (about 2.55 g) about 70%.

EXAMPLE 3:

Preparation of 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (1) using DBH (Figure 1)

In a single neck round bottom (RB) flask, 1,4,5, 8-naphthalenetetracarboxylic dianhydride (about 2.68 g, about 10 mmol) is slurried in concentrated sulfuric acid (about 20 mL) (alternatively oleum or vitriolic acid may also be employed) at about 0 °C to about 25 °C, preferably about 24 °C and the mixture is stirred for about 5 min to achieve dissolution. 5,5- dimethyl-l,3-dibromohydantoin (DBH) (about 1.57 g, about 5.5 mmol) is added in portions over a period of about 1 h and the RB flask is tightly stoppered (in order to avoid the escape of bromine from the reaction mixture). The resulting brown solution is stirred at about 0 °C to about 25 °C for about 12 h. The brown reaction mixture is poured into crushed ice to precipitate the solid. The precipitated solid is filtered, washed with water then with methanol, and finally dried in vacuum to afford 2-bromo-NDA 1 as a pale yellow solid, which is recrystallized from DMF to obtain the pure product as white crystals ( about 2.42 g, about 70%); IR (KBr, cm^"1): 1787, 1731, 1192, 1373, 1174, 1149, 1091, 983, 935; 1H MR (400 MHz, DMSO-de): δ_Η 8.71 (s, 1H), 8.58-8.56 (d, J = 7.6 Hz, 1H), 8.22-8.20 (d, J = 7.6 Hz, 1H); ¹³C NMR (100 MHz, DMSO-d₆) (Figure 12): 5_C 168.1, 160.0, 159.4, 137.4, 131.6, 131.5, 130.6, 129.2, 128.3, 125.3, 124.5, 121.8; Elemental analysis (i.e., the composition by weight percentage of each element present in the organic compound). Found (experimental value): C, 48.47, H, 0.85; Calcd (theoretically calculated value): C, 48.45; H, 0.87 for

EXAMPLE 4:

Preparation of 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (2) using DBH (Figure 1)

In a single neck RB flask, NDA (about 2.68 g, about 10 mmol) is slurried in concentrated sulfuric acid (about 25 mL) (alternatively oleum or vitriolic acid may also be employed) at about 0 °C to about 25 °C the mixture is stirred at about 0 °C to about 25 °C for about 5 min to achieve dissolution. DBH (about 3.57 g, about 15 mmol) is added in four portions over a period of about 1 h atabout 0 °C to about 25 °C . The resulting brown solution is stirred at about 50 °C for about 10 h. The mixture is poured into crushed ice to precipitate the solid. The precipitated solid is filtered, washed with water then with methanol, and finally dried under vacuo to afford a crude product which is further purified by crystallization in DMF. During crystallization, the partially ring opened side product preferentially gets crystallized leaving supernatant with pure product 2,6-dibromo- DA 2, which is further purified by precipitation method ( about 3.49 g, about 82% ); IR (KBr, cm^"1): 1787, 1733, 1191, 1172, 1150, 1093, 985, 936; 1H MR (400 MHz, DMSO-d₆): δ_Η 8.78 (s, 2H); ¹³C MR (100 MHz, DMSO-de) (Figure 13): 5_C 157.9, 156.4, 137.5, 129.4, 127.4, 124.2, 123.4; Elemental analysis. Found: C, 39.42; H, 0.45; Calcd: C, 39.47; H, 0.47 for Ci₄H₂Br₂0₆.

EXAMPLE 5:

Preparation of 2,3,6,7-Tetrabromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (3) using DBH (Figure 1)

In a single neck RB flask NDA (about 2.68 g, about 10 mmol) is slurried in concentrated sulfuric acid (about 50 mL) (alternatively oleum or vitriolic acid may also be employed) at about 0 °C to about 25 °C . DBH (about 8.57 g, about 30 mmol) is added in portions and tightly stoppered with solid glass stopper. The resulting brown solution is stirred at about 0 °C to about 25 °C for about 4 h and then the mixture is heated at about 80 °C for about 12 h. The mixture is poured into crushed ice to precipitate the solid. The precipitated solid is filtered, washed with water then with methanol, and finally dried under vacuum to obtain 2,3,6,7-tetrabromo- DA 3 as a yellow solid (about 5.6 g, about 96%); IR (KBr, cm^"1): 1787, 1733, 1507, 1499, 1421, 1373, 1335, 1188, 1146, 1096, 988, 937, 778, 702, 570; Elemental anaysis. Found: C, 28.67; Calcd: C, 28.80 for Ci₄Br₄0₆ (Figure 14).

EXAMPLE 6:

Preparation of N^V'-Bis(n-octyl)-2-bromo-l,4,5,8-naphthalenetetracarboxylic diimide (4) (Figure 2)

A mixture of 2-bromo- DA 1 (about 867 mg, about 2.5 mmol), «-octylamine (about 1.24 mL, about 7.5 mmol), and acetic acid (about 25 mL) is stirred at about 90 °C for about 3 h. The mixture is cooled to about 0 °C to about 25 °C , precipitate is collected by filtration, washed with methanol and dried under vacuum to obtain N,A^-bis(«-octyl)-2-bromo- DI 4 as a pale yellow crystalline solid (about 1.13 g, about 80%); IR (CHC1₃, cm^"1): 3063, 2954, 2919, 2850, 1705, 1656, 1568, 1438, 1371, 1331, 1251, 1238, 1187, 1104, 1076, 780; 1H NMR (400 MHz, CDC1₃): δ_Η 8.94 (s, 1H), 8.83-8.81(d, J = 8 Hz, 1H), 8.77-8.75 (d, J= 8 Hz, 1H), 4.22-4.16 (apparent q, J = 8 Hz, 4H, 2CH₂), 1.78-1.69 (m, 4H, 2CH₂), 1.43-1.25(m, 20H, IOCH₂), 0.89-0.86 (t, J= 6.4 Hz, 6H, 2CH₃); ¹³C NMR (100 MHz, CDC1₃) (Figure 15): 5c 162.4, 161.8, 161.7, 138.4, 131.6, 130.7, 128.6, 128.6, 126.8, 126.0, 126.0, 125.7, 123.9, 41.5, 41.1, 31.8, 29.3, 29.26, 29.21, 29.1, 28.0, 27.9, 27.1, 27.0, 22.6, 14.0; Elemental analysis. Found: C, 63.21, H, 6.50; N, 4.90; Calcd: C, 63.27; H, 6.55; N, 4.92 for C₃₀H₃₇BrN₂O₄. HRMS (APCI) (m/z): calcd for C₃₀H₃₇BrN₂O₄ [M + H]⁺, 569.2015, found 569.1989 (Figure 21).

EXAMPLE 7:

Preparation of N /V'-Bis-(n-octyl)-2-(n-octylamino)-l,4,5,8-naphthalenetetracarboxylic diimide (8)

TWO STEP REACTION (Figure 4)

A mixture of N,N'-bis(«-octyl)-2-bromo-NDI 4 (about 569 mg, about 1 mmol) and n- octylamine (about 0.2 mL, about 1.25 mmol) in toluene (about 10 mL) is refluxed for about 3 h under nitrogen. After completion of the reaction, toluene is removed on a rotary evaporator and the product is purified by column chromatography on silica gel (100-200 mesh) column eluted with 25% dichloromethane in hexane. N,N'-Bis-(«-octyl)-2-(«-octylamino)-NDI 8 is obtained as red crystals (about 570 mg, about 96%); IR (CHC1₃, cm^"1): 3250, 2957, 2923, 2854, 1707, 1675, 1635, 1587, 1521, 1459, 1323, 1279, 1184, 875, 786; 1H NMR (400 MHz, CDC1₃): δ_Η 10.14-10.12 (t, J = 4.8 Hz, 1H, N-H), 8.66-8.64 (d, J = 8 Hz, 1H, Ar-H), 8.35- 8.33 (d, J = 8 Hz, 1H, Ar-H), 8.21 (s, 1H, Ar-H), 4.20-4.14 (m, 4H, 2CH₂), 3.60-3.55 (q, J = 7.2 Hz, 2H, CH₂), 1.86-1.79 (quin, J = 7.2 Hz, 2H, CH₂), 1.76-1.69 (quin, J = 7.2 Hz, 4H, 2CH₂), 1.47-1.28 (m, 30H, 15CH₂), 0.91-0.87 (t, J = 6.8 Hz, 9H, 3CH₃); ¹³C NMR (100 MHz, CDC1₃) (Figure 18): 5_C 166.4, 163.5, 163.2, 163.1, 152.5, 131.4, 129.7, 128.1, 126.3, 124.5, 123.7, 119.9, 119.5, 99.9, 43.5, 41.0, 40.5, 31.97, 31.93, 29.6, 29.5, 29.4, 29.4, 29.34, 29.31, 28.2, 27.3, 27.2, 27.1, 22.7, 14.2; Elemental analysis. Found: C, 73.79; H, 8.74; N, 6.79; Calcd: C, 73.87; H, 8.97; N, 6.80 for C₃₈H₅N₃0₄. HRMS (APCI) (m/z): calcd for C₃₈H₅₆N₃0₄ [M + H]⁺, 618.4271, found 618.4247 (Figure 24).

ONE-STEP REACTION DI 8 is synthesized in a single step method by reacting 2-Bromo-l, 4,5,8- naphthalenetetracarboxylic dianhydride 1 (2mmol, 694 mg) with «-octylamine (4.692g- 6ml, as a solvent) at a temperature of about 50 °C to about 100 °C and refluxing under nitrogen for a duration of about 10 to about 32 hours, particularly about 10 hours. Completion of the reaction is monitored by TLC. After completion of the reaction, excess «-octylamine is removed on a rotary evaporator and the product is purified by column chromatography on silica gel column, eluted with 50% dichloromethane in hexane to obtain NDI 8.

EXAMPLE 8:

Preparation of N^V'-Bis(n-octyl)-2,6-dibromo-l,4,5,8-naphthalenetetracarboxylic diimide (5) (Figure 2)

A mixture of 2,6-dibromo-NDA 2 (about 1.06 g, about 2.5 mmol), «-octylamine (about 1.24 mL, about 7.5 mmol), and acetic acid (about 25 mL) is stirred under nitrogen atmosphere at about 90 °C for about 4h. The mixture is cooled to about 0 °C to about 25 °C The precipitate is separated by filtration, washed with methanol and dried under vacuo to obtain iV,iV-bis(«- octyl)-2,6-dibromo-NDI 5 as a yellow crystalline solid (about 1.21g, about 75%); IR (CHC1₃ cm^"1): 3058, 2917, 2848, 2954, 1701, 1655, 1561, 1437, 1372, 1315, 1253, 1234, 1218, 1189,1107, 957, 863, 786, 765, 722, 614, 626, 572; 1H-NMR (400 MHz, CDC1₃): δ_Η 8.99 (s, 1H, Ar-H), 4.20-4.16 (t, J = 7.6 Hz, 4H, 2CH₂), 1.77-1.69 (quin, J = 7.6 Hz, 4H, 2CH₂), 1.42-1.27 (m, 20H, 10CH₂), 0.89-0.86 (t, J = 6.8 Hz, 6H, 2CH₃); ¹³C NMR (100 MHz, CDCI₃) (Figure 16): 5_C 160.9, 160.8, 139.2, 128.4, 127.8, 125.5, 124.2, 41.7, 31.9, 29.4, 29.3, 28.0, 27.2, 22.7, 14.2. Elemental analysis. Found: C, 55.65, H, 5.63; N, 4.16; Calcd: C, 55.57; H, 5.60; N, 4.32 for C₃₀H₃₆Br₂N₂O₄. HRMS (APCI) (m/z): calcd for C₃₀H₃₆Br₂N₂O₄ [M + H]⁺, 649.1100, found 649.1069 (Figure 22).

EXAMPLE 9:

Preparation of N^/V'-Bisin-octy^^^^^-tetrabromo-l^^^-naphthalenetetracarboxylic diimide (7) (Figure 2)

2,3,6,7-Tetrabromo-NDA 3 (about 2.91 g, about 5 mmol) and «-octylamine (about 2.48 mL, about 15 mmol) in acetic acid (about 100 mL) are stirred under a nitrogen atmosphere at about 120 °C. The reaction is stopped before the color of the reaction mixture changes to red (about 30 min). The reaction mixture is cooled to about 0 °C to about 25 °C and poured into water, then filtered. The obtained yellow solid is washed with water, thereafter dried under vacuo, and the crude product 6 is used directly for the next reaction without further purification.

A solution of the intermediate 6 and PBr₃ (about 0.94 mL, about 10 mmol) in toluene (about 50 mL) is refluxed for about 6 h under a N₂ atmosphere. The mixture is cooled to about 0 °C to about 25 °C and then poured into water (about 200 mL). The aqueous phase is extracted with toluene (about 3 x 50 mL), and the combined organic layers are dried over Na₂S0₄. The solvent is removed under reduced pressure and the crude product is washed with methanol to obtain N,A^-bis(«-octyl)-2,36,7-tetrabromo-NDI 7 as a yellow crystalline solid (about 2.4 g, about 60%). IR (CHC1₃ cm^"1): 2956, 2917, 2851, 1713, 1669, 1377, 1288, 1156, 788, 576; 1H NMR (400 MHz, CDC1₃): 4.22-4.18 (t, J = 7.6 Hz, 4H), 1.79-1.71 (m, 4H), 1.42-1.25 (m, 20H), 0.88-0.86 (t, J = 6.4 Hz, 6H). ¹³C NMR (100 MHz, CDC1₃) (Figure 17): 5c 159.9, 135.6, 126.7, 125.7, 43.0, 31.9, 29.38, 29.36, 28.1, 27.2, 22.7, 14.2; Elemental analysis. Found: C, 44.01; H, 4.26; N, 3.22; Calcd: C, 44.69; H, 4.25; N, 3.47 for C₃₀H₃₄Br₄N₂O₄. HRMS (APCI) (m/z): calcd for C₃₀H₃₄Br₄N₂O₄ [M + H]⁺, 806.9289, found 806.9283 (Figure 23).

EXAMPLE 10:

Preparation of N^V'-Bis-(n-octyl)-2,6-di(n-octylamino)-l,4,5,8- naphthalenetetracarboxylic diimide (9)

TWO STEP REACTION (Figure 4)

A mixture of N,N'-bis(«-octyl)-2,6-dibromo-NDI 5 (about 648 mg, about 1 mmol) and n- octylamine (about 0.41 mL, about 2.5 mmol) in toluene (about 10 mL) is refluxed for about 12 h under nitrogen. Completion of the reaction is monitored by TLC. After completion, toluene is removed on a rotary evaporator, and the product is purified by column chromatography on silica gel (100-200 mesh) column eluted with 15% dichlorom ethane in hexane. N,N'-bis(«-octyl)-2,6-di(«-octylamino)-NDI 9 is obtained as dark green crystals (about 685 mg, about 92%); IR (CHC1₃, cm^"1): 3283, 2956, 2925, 2854, 1682, 1631, 1587, 1487, 1465, 1318, 1186, 886, 789; 1H NMR (400 MHz, CDC1₃): δ_Η 9.33-9.31 (t, J = 4.6 Hz, 2H, N-H), 8.10 (s, 2H, Ar-H), 4.17-4.13 (t, J =8 Hz, 4H, 2CH₂), 3.50-3.45 (q, J = 8 Hz, 4H, CH₂), 1.83-1.67 (m, 8H), 1.36-1.28 (m, 40H, 20CH₂), 0.89-0.86 (t, J = 6.6 Hz, 12H, 4CH₃); ¹³C NMR (100 MHz, CDC1₃) (Figure 19): 5_C 166.3, 163.2, 149.3, 125.9, 121.2, 118.4, 101.9, 53.5, 43.3, 40.6, 31.98, 31.97, 29.6, 29.5, 29.46, 29.4, 29.3, 28.2, 27.4, 27.3, 22.8, 14.2; Elemental analysis. Found: C, 73.59, H, 9.70; N, 7.41; Calcd: C, 74.15; H, 9.74; N, 7.52 for C46H72N4O4. HRMS (APCI) (m/z): calcd for C46H73N4O4 [M + H]⁺, 745.5632, found 745.5596 (Figure 25).

ONE-STEP REACTION

DI 9 is synthesized in a single step method by reacting 2,6-Dibromo-l,4,5,8- naphthalenetetracarboxylic dianhydride 2 (2 mmol, 852 mg) with n-octylamine (7.8g- 10ml, as a solvent) at a temperature of about 50 °C to about 100 °C, refluxed under nitrogen for a duration of about 10 to about 32 hours. Completion of the reaction is monitored by TLC. After completion of the reaction, excess n-octylamine is removed on a rotary evaporator and the product is purified by column chromatography on silica gel column, eluted with 25% dichloromethane in hexane to obtain NDI 9.

EXAMPLE 11:

Preparation of N^V'-Bis-(n-octyl)-2,3,6,7-tetra(n-octylamino)-l,4,5,8- naphthalenetetracarboxylic diimide (10)

TWO STEP REACTION (Figure 4)

A mixture of N,N'-bis-(«-octyl)-2,3,6,7-tetrabromo-l,4,5,8-naphthalenetetracarboxylic diimide i.e. NDI 7 (about 806 mg, about 1 mmol) and «-octylamine (about 0.83 mL, about 5 mmol) in toluene (about 10 mL) is refluxed for about 10 h under nitrogen. Completion of the reaction is monitored by TLC. After completion, toluene is removed on a rotary evaporator and the product is purified by column chromatography on silica gel (100-200 mesh) column eluted with 5% dichloromethane in hexane, N,N'-Bis-(«-octyl)-2,3,6,7-tetra(«-octylamino)- NDI 10 is obtained as dark green crystals (about 980 mg, about 98%). IR (CHC1₃, cm^"1): 3264, 2955, 2921, 2850, 1643, 1629, 1577, 1520, 1454, 1283, 1180, 1142, 1124, 843, 791, 724; 1H NMR (400 MHz, CDC1₃): δ_Η 9.39 (bs, 4H), 4.21-4.17 (t, J = 7.6 Hz, 4H, 2CH₂), 3.38-3.35 (apparent t, J = 6.4 Hz, 8H, 4CH₂), 1.76-1.68 (m, 4H, 2CH₂), 1.54-1.46 (m, 8H, 4CH₂), 1.29-1.21 (m, 60H, 30CH₂), 0.89-0.85 (m, 18H, 6CH3); ¹³C NMR (100 MHz, CDC1₃) (Figure 20): 5_C 166.1, 147.1, 117.1, 108.0, 45.2, 40.4, 32.0, 31.9, 31.3, 29.5, 29.45, 29.42, 29.3, 28.2, 27.4, 27.2, 22.8, 22.7, 14.3, 14.2; Elemental analysis. Found: C, 74.22, H, 10.30; N, 8.23; Calcd: C, 74.50; H, 10.69; N, 8.41 for CeiHioeNeC HRMS (APCI) (m/z): calcd. for C62H107N6O4 [M + H]⁺, 999.8354, found 999.8328 (Figure 26).

ONE-STEP REACTION

NDI 10 is synthesized in a single step method by reacting 2,3, 6,7-Tetrabromo-l, 4,5,8- naphthalenetetracarboxylic dianhydride 3 (2 mmol, 1.16g) with «-octylamine (12g- 16ml, as a solvent) at a temperature of about 50 °C to about 100 °C, refluxed under nitrogen for a duration of about 10 to about 32 hours. Completion of the reaction is monitored by TLC. After completion of the reaction, excess «-octylamine is removed on a rotary evaporator and the product is purified by column chromatography on silica gel column, eluted with 15% dichloromethane in hexane to obtain NDI10.

EXAMPLE 12:

Photophysical properties of core substituted naphthalene diimides 8, 9 and 10

The core substituents have tremendous influence on the optical properties of NDIs compared to corresponding imide substituents. The UV-vis absorption and fluorescence characteristics of imide substituted NDIs 4, 5 and 7 and both imide and core substituted NDIs 8-10 in chloroform are studied (Figure 10). The absorption spectra of N,A^-bis(¾-octyl)-bromo-NDIs 4, 5 and 7 exhibits S₀-S₁ electronic transitions in the range of 300-460 nm (Figure 5). The monobromo- and dibromo-NDIs 4 and 5 exhibits vibronic absorption bands (340, 360, 380 and 390 nm peaks for 4 and 352, 364, 387 and 408 nm peaks for 5 respectively) with absorption maxima at 360 and 364 respectively. However, relatively broad absorption spectrum with remarkable red-shift of 50 nm is observed for tetrabromo-NDI 7 with prominent absorption maxima at 402 and 427 nm. This pronounced red-shift correlates with the number of bromine atoms on the aromatic core of NDI. The prominent vibronic fine structure of the absorption band indicates the rigid nature of the chromophores and its energy in the order of ca. 1300 cm^"1 (0.16 eV) corresponds to the skeletal vibrations of the aromatic system. Introduction of «-octylamino substituents at the naphthalene core in compounds 8-10 lead to characteristic display of absorption and emission properties as shown in Figure 6. Core substituted NDIs 8 and 9 exhibit band I absorption in the region 300-400 nm. Interestingly for NDI 10 with four «-octylamino substituents, the band I red shifts to 461 nm. Furthermore, core substitution causes interesting electronic transitions in the visible region with new absorption bands at 527, 620 and 639 nm corresponding to NDI 8, 9 and 10 respectively that covers wide visible spectral range (Figure 6a and Table 1). Because of their absorption in the visible region, solutions of NDIs 8, 9 and 10 in chloroform display bright colors (red, blue and greenrespectively) visible to naked eye under day light (Figure 6b). The increase in the number of electron-donating «-octylamino substituents at the naphthalene core evokes a bathchromic-shift of 93 and 112 nm to the new absorption band of NDIs 9 and 10 compared to mono-«-octylamino- substituted NDI 8.

Next, the effect of core substitution on the fluorescence emission characteristics of NDIs is studied. The imide substituted bromo-NDIs 4, 5 and 7 do not show any significant fluorescence properties. However solutions of core substituted NDIs 8, 9 and 10 with excitation wavelengths corresponding to their new absorption bands (497, 577 and 597 nm respectively) as shown in Figure 6a and Table 2 exhibit bright fluorescence emission with emission maxima at 560, 649, and 693 nm respectively (Figure 6c and Table 2). The fluorescence colors of solutions of core substituted NDIs 8-10 in chloroform with common excitation wavelength of 365 nm is shown in Figure 6d. Thus the electron donating alkylamino substituents transforms NDIs to valuable fluorophores with relatively good fluorescence quantum yields (Table 2) and tunable emission wavelengths from blue to red spectral region. The quantum yields of compounds 9 and 10 match with the data reported in literature. The absorbance and fluorescence data of NDI 6, 7, 9 and 10 match with the reported data in the literature further confirming the integrity of the product obtained through the DBH bromination method of the present disclosure. In general the study also shows that the core substitution strongly influence the electronic and optical properties of NDIs.

Table 1: Absorption maxima ( »_a^) and molar absorptivity coefficients (ε) of compounds 1-3 in DMF and 4-10 in chloroform

λ /nm -1 -1

Compound max ε Μ cm

NDA 1 313 15,560

NDA 2 314 22,480

NDA 3 372 27,480

NDI 4 360 34,440

NDI 5 364 28,540 NDI 7 402 22500

427 22,706

NDI 8 371 28254

527 28,138

NDI 9 365 24840

620 41,600

NDI 10 461 11908

639 30,600

Table 2: Fluorescence emission parameters of core substituted NDIs 8-10 in chloroform

where ³λ is excitation wavelength, is emission maximum wavelength, ^£ φ = Quantum yield.

EXAMPLE 13:

Preparation of 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (1) using TBCA (Figure 7)

In a single neck round bottom (RB) flask, 1,4,5,8-naphthalenetetracarboxylic dianhydride (about 2.68 g, about 10 mmol) is slurried in concentrated sulfuric acid (about 25 mL) (alternatively oleum or vitriolic acid may also be employed) at about 0 °C to about 25 °C , the mixture is stirred for about 5 min to obtain dissolution. Tribromoisocyanuric acid (TBCA) (about 1.83 g, about 5 mmol) is added in portions over a period of about 1 h and the RB flask is tightly stoppered (in order to avoid the escape of bromine from the reaction mixture). The resulting brown solution is stirred at about 0 °C to about 25 °C for about 12 h. The brown reaction mixture is poured into crushed ice to precipitate the solid. The precipitated solid is filtered, washed with water then with methanol, and finally dried in vacuum to afford 2- bromo-NDA 1 as a pale yellow solid, which is recrystallized from DMF to obtain the pure product as white crystals ( about 2.42 g, about 70%); IR (KBr, cm^"1): 1787, 1731, 1192, 1373, 1174, 1149, 1091, 983, 935; 1H NMR (400 MHz, DMSO-d₆): δ_Η 8.71 (s, 1H), 8.58-8.56 (d, J = 7.6 Hz, 1H), 8.22-8.20 (d, J = 7.6 Hz, 1H); ¹³C NMR (100 MHz, DMSO-d₆): 5_C 168.11, 160.02, 159.40, 137.41, 131.64, 131.56, 130.69, 129.29, 128.37, 125.38, 124.58, 121.83. Elemental analysis. Found: C, 48.47, H, 0.85; Calcd: C, 48.45; H, 0.87 for Ci₄H₃Br0₆.

EXAMPLE 14:

Preparation of 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (2) using TBCA (Figure 7)

In a single neck RB flask, NDA (about 2.68 g, about 10 mmol) is slurried in concentrated sulfuric acid (about 25 mL) (alternatively oleum or vitriolic acid may also be employed) at about 0 °C to about 25 °C and the mixture is stirred at about 0 °C to about 25 °C for about 5 min to achieve dissolution. TBCA (about 3.66 g, about 10 mmol) is added in four portions over a period of about 1 h at about 0 °C to about 25 °C . The resulting brown solution is stirred at about 0 °C to about 25 °C for about 18 h. The mixture is poured into crushed ice to precipitate the solid. The precipitated solid is filtered, washed with water then with methanol, and finally dried under vacuum to afford crude product which is recrystallized from DMF to get pure product 2,6-dibromo-NDA 2 as white crystals ( about 3.23 g, about 76% ); IR (KBr, cm^"1): 1787, 1733, 1191, 1172, 1150, 1093, 985, 936; 1H NMR (400 MHz, DMSO-d₆): 1H NMR (400 MHz, DMSO-d₆): δ_Η 8.78 (s, 2H); ¹³C NMR (100 MHz, DMSO-d₆): 5_C 157.9, 156.4, 137.5, 129.4, 127.4, 124.2, 123.4. Elemental analysis. Found: C, 39.42; H, 0.45; Calcd: C, 39.47; H, 0.47 for Ci₄H₂Br₂0₆.

EXAMPLE 15:

Preparation of 2,3,6,7-Tetrabromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (3) using TBCA (Figure 7)

In a single neck RB flask, NDA (about 2.68 g, about 10 mmol) is slurried in concentrated sulfuric acid (about 50 mL) (alternatively oleum or vitriolic acid may also be employed) at about 0 °C to about 25 °C . TBCA (about 9.15 g, about 25 mmol) is added in portions and tightly stoppered with solid glass stopper. The resulting brown solution is stirred at about 0 °C to about 25 °C for about 24 h and then the mixture is heated at about 80 °C for about 8 h. The mixture is poured into crushed ice to precipitate the solid. The precipitated solid is filtered, washed with water then with methanol, and finally dried under vacuum to obtain 2,3,6,7-tetrabromo-NDA 3 as yellow solid (about 5.48 g, about 94%); IR (KBr, cm^"1): 1787, 1733, 1507, 1499, 1421, 1373, 1335, 1188, 1146, 1096, 988, 937, 778, 702, 570; Elemental anaysis. Found: C, 28.67; Calcd: C, 28.80 for Ci₄Br₄0₆.

EXAMPLE 16:

Preparation of N^V'-Bis-(n-butyl)-2-(n-butylamino)-l,4,5,8-naphthalenetetracarboxylic diimide (11)

ONE-STEP REACTION (Figure 8a)

A mixture of 2-bromo- DA 1 (about 694 mg, about 2 mmol) and «-butylamine (about 8 mL) is refluxed for about 10 h under nitrogen. Completion of the reaction is monitored by TLC. After completion of the reaction, excess n-butylamine is removed on a rotary evaporator and the product is purified by column chromatography on silica gel (100-200 mesh) column eluted with 50% dichloromethane in hexane. N,N'-Bis-(«-butyl)-2-(«-butylamino)-NDI 11 is obtained as red crystals (about 540 mg, about 60%); IR (CHC1₃, cm^"1): 3254, 2959, 2926, 2854, 1704, 1673, 1634, 1589, 1519, 1460, 1324, 1016, 786; 1H NMR (400 MHz, CDC1₃): δ_Η 10.13 (broad t, 1H, N-H), 8.66-8.64 (d, J = 8 Hz, 1H, Ar-H), 8.35-8.33 (d, J = 8 Hz, 1H, Ar- H), 8.22 (s, 1H, Ar-H), 4.21-4.15 (m, 4H, 2CH₂), 3.61-3.56 (q, J = 7.2 Hz, 2H, CH₂), 1.86- 1.79 (quin, J= 7.2 Hz, 2H, CH₂), 1.76-1.69 (quin, J= 7.2 Hz, 4H, 2CH₂), 1.47-1.28 (m, 30H, 15CH₂), 0.91-0.87 (t, J = 6.8 Hz, 9H, 3CH₃); ¹³C MR (100 MHz, CDC1₃) (Figure 27): 5_C 166.4, 163.5, 163.24, 163.22, 152.5, 131.4, 129.7, 128.1, 126.3, 124.5, 123.7, 119.9, 119.5, 99.9, 43.1, 40.8, 40.3, 31.6, 30.3, 20.6, 20.4, 20.3, 14.0, 13.95, 13.92; HRMS (APCI) (m/z): calcd for C₂₆H₃iN₃0₄ [M + H]⁺, 450.2393, found 450.2395 (Figure 29).

TWO-STEP REACTION (Figure 8b,8c)

DI 11 is synthesized in a two-step method by first reacting 2-Bromo-l, 4,5, 8- naphthalenetetracarboxylic dianhydride (1) (2.5 mmol, 867 mg) with an amount of n- butylamine equivalent to about 3 times the amount of 2-Bromo-l, 4,5, 8- naphthalenetetracarboxylic dianhydride (1) (7.5 mmol, 0.55g, 0.74ml) (i.e. 3 : 1), in acetic acid and stirring under nitrogen atmosphere at a temperature of about 80 °C to about 90 °C for about 3 hours. The mixture is cooled to room temperature (about 0 °C to about 25 °C). The precipitate is separated by filtration, washed with methanol and dried under vacuo to obtain N,N'-Bis(«-butyl)-2-bromo-l,4,5,8-naphthalenetetracarboxylic diimide (a). Further, N,N'-Bis(«-butyl)-2-bromo-l,4,5,8-naphthalenetetracarboxylic diimide (a) (1 mmol, 0.46g) is reacted with an amount of n-butylamine equivalent to about 1.5 times the amount of the diimide (1.5 mmol, 0.10g, 0.15ml) (i.e. 1.5: 1), in toluene at a temperature of about 50 °C to about 110 °C, refluxed under nitrogen for a duration of about 2 hours to about 6 hours. After completion of the reaction, toluene is removed on a rotary evaporator, the product is purified by column chromatography on silica gel column, eluted with about 25% dichloromethane in hexane, to obtain DI 11 (Figure 8b, 8c).

EXAMPLE 17:

Preparation of N,N'-Bis-(«-butyl)-2,6-di(«-butylamino)-l,4,5,8- naphthalenetetracarboxylic diimide (12)

ONE-STEP REACTION (Figure 8a)

A mixture of 2,6-dibromo- DA 2 (about 852 mg, about 2 mmol) and «-butylamine (about 12 mL) is refluxed for about 24 h under nitrogen. Completion of the reaction is monitored by TLC. After completion, excess «-butylamine is removed on a rotary evaporator, and the product is purified by column chromatography on silica gel (100-200 mesh) column eluted with 25% dichloromethane in hexane. N,N'-bis(«-butyl)-2,6-di(«-butylamino)-NDI 12 is obtained as dark blue crystals (520 mg, 50%); IR (CHC1₃, cm^"1): 3286, 2959, 2926, 2854, 1679, 1632, 1596, 1489, 1465, 1320, 1209, 789; 1H NMR (400 MHz, CDC1₃): δ_Η 9.33-9.31 (t, J= 4.6 Hz, 2H, N-H), 8.10 (s, 2H, Ar-H), 4.17-4.13 (t, J=8 Hz, 4H, 2CH₂), 3.50-3.45 (q, J = 8 Hz, 4H, CH₂), 1.83-1.67 (m, 8H), 1.36-1.28 (m, 40H, 20CH₂), 0.89-0.86 (t, J = 6.6 Hz, 12H, 4CH₃); ¹³C NMR (100 MHz, CDC1₃) (Figure 28) : 5_C 166.2, 163.1, 149.2, 125.8, 121.1, 118.3, 101.8, 43.0, 40.3, 31.6, 30.3, 29.8, 20.6, 20.4, 14.0, 13.9; HRMS (APCI) (m/z): calcd for C₃₀H₄oN₄0₄ [M + H]⁺, 521.3128, found 521.3127 (Figure 30).

TWO-STEP REACTION (Figure 8b, 8c)

NDI 12 is synthesized in a two-step method by first reacting 2,6-Dibromo-l, 4,5,8- naphthalenetetracarboxylic dianhydride (1) with an amount of n-butylamine equivalent to about 3 times the amount of 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (i.e. 3 : 1), in acetic acid, at a temperature of about 80 °C to about 90 °C for about 4 hours to obtain N,N'-Bis(«-butyl)-2,6-dibromo-l,4,5,8-naphthalenetetracarboxylic diimide (b). Further, N,N'-Bis(«-butyl)-2,6-dibromo-l,4,5,8-naphthalenetetracarboxylic diimide (b) (1 mmol, 0.53g) is reacted with an amount of n-butylamine equivalent to about 2.5 times the amount of the diimide (2.5 mmol, 0.18g, 0.24ml) (i.e. 2.5: 1), in toluene at a temperature of about 50 °C to about 110 °C refluxed under nitrogen for a duration of about 8 hours to about 12 hours. Completion of the reaction is monitored by TLC. After completion, toluene is removed on a rotary vapour, the product is purified by column chromatography on silica gel column and eluted with 15% dichloromethane in hexane to obtain DI 12 (Figure 8b, 8c).

EXAMPLE 18:

Preparation of N^V'-Bis-(n-butyl)-2,3,6,7-tetra(n-butylamino)-l,4,5,8- naphthalenetetracarboxylic diimide (13)

ONE-STEP REACTION (Figure 8a)

A mixture of Tetrabromo- DA 3 (about 1.16 g, about 2 mmol) and «-butylamine (about 15 mL) is refluxed for about 32 h under nitrogen. Completion of the reaction is monitored by TLC. After completion, «-butylamine is removed on a rotary evaporator and the product is purified by column chromatography on silica gel (100-200 mesh) column eluted with 15% dichloromethane in hexane, N,N'-Bis-(«-butyl)-2,3,6,7-tetra(«-butylamino)- DI 13 is obtained as dark green crystals (about 610 mg, about 46%). IR (CHC1₃, cm^"1): 3274, 2961, 2916, 2850, 1645, 1629, 1577, 1462, 1263, 1093, 1026, 798; 1H NMR (400 MHz, CDC1₃): δ_Η 9.39 (bs, 4H), 4.21-4.17 (t, J = 7.6 Hz, 4H, 2CH₂), 3.38-3.35 (apparent t, J = 6.4 Hz, 8H, 4CH₂), 1.76-1.68 (m, 4H, 2CH₂), 1.54-1.46 (m, 8H, 4CH₂), 1.29-1.21 (m, 60H, 30CH₂), 0.89- 0.85 (m, 18H, 6CH₃); ¹³C NMR (100 MHz, CDC1₃): 5_C 166.17, 147.11, 117.16, 108.05, 45.23, 40.49, 32.01, 31.91, 31.39, 29.59, 29.45, 29.42, 29.34, 28.20, 27.47, 27.25, 22.80, 22.77, 14.24, 14.21; HRMS (APCI) (m/z): calcd. for C₃₈H₅₈N₆0₄ [M + H]⁺, 663.4598, found 663.4563 (Figure 31).

TWO-STEP REACTION (Figure 8b, 8c)

NDI 13 is synthesized in a two-step method by first reacting 2,3,6,7-Tetrabromo-l,4,5,8- naphthalenetetracarboxylic dianhydride (3) with an amount of n-butylamine equivalent to about 3 times the amount of 2,3,6,7-Tetrabromo-l,4,5,8-naphthalenetetracarboxylic dianhydride (i.e. 3 : 1), in acetic acid, at a temperature of about 120°C for about 30 minutes to obtain a crude product which is an intermediate (c). Further, the solution of the intermediate (c) and PBr₃ in toluene is refluxed for 6 hours under a nitrogen atmosphere. The mixture is cooled to room temperature (about 0 °C to about 25 °C) and then poured into water. The aqueous phase is extracted with toluene and the combined organic layers are dried over sodium sulfate. The solvent is removed under reduced pressure and the crude product is washed with methanol to obtain N,N'-Bis(«-butyl)-2,3,6,7-dibromo-l,4,5,8- naphthalenetetracarboxylic diimide (d).

Further, N,N'-Bis(«-butyl)-2,3,6,7-tetrabromo-l,4,5,8-naphthalenetetracarboxylic diimide (d) (1 mmol, 0.69g) is reacted with an amount of n-butylamine equivalent to about 5 times the amount of the diimide (5 mmol, 0.365, 0.5ml) (i.e. 5: 1), in toluene at a temperature of about 50 °C to about 110 °C for a duration of about 6 hours to about 12 hours to arrive at DI 13 (Figure 8b, 8c).

EXAMPLE 19:

Photophysical properties of Core substituted NDIs 11, 12 and 13

The optical properties of NDIs are mainly influenced by the core substitution. The UV-Vis absorbance and fluorescence spectral properties of core substituted NDIs 11, 12 and 13 are studied and are shown in Figure 9. Core substituted NDIs 11 and 12 exhibit band I absorption in the region 300-400 nm upon introducing n-butylamine. The compound 13 with four n- butylamino substituents on the core interestingly shows a shift in this band I to 458 nm. Moreover, in the visible region new absorption bands at 525, 619 and 638 nm are observed corresponding to NDI 11, 12 and 13 respectively that cover wide visible spectral range (Figure 9a). Interestingly, NDIs 12 and 13 display a remarkable bathchromic-shift of 94 and 113 nm compared to mono-«-butylamino- substituted NDI 11 that shows the effect of increase in number of electron-donating substituents at the naphthalene core. However solutions of core substituted NDIs 11, 12 and 13 with excitation wavelengths corresponding to their new absorption bands (497, 577, and 600 nm respectively) as shown in Figure 9a exhibit bright fluorescence emission with emission maxima at 561, 655, and 692 nm respectively (Figure 9b). Compounds 11, 12 and 13 in chloroform exhibit bright colors (red, blue and green respectively) visible to naked eye under day light due to absorption in visible region(Figure 9c) and their bright fluorescence colors with common excitation wavelength of 365 nm is shown in Figure 9d. Hence, emission wavelengths of NDIs can be tuned in wide visible spectral region by varying electron donating alkylamino substituents. The absorbance and fluorescence data of NDI 11, 12 and 13 are found to be similar with the NDIs substituted with n-octylamine reported in the literature further confirming the integrity of the product obtained through the TBCA bromination method.

EXAMPLE 21:

Comparison of yields of brominated naphthalene dianhydride (NDA- Br) obtained using DBH/TBCA as brominating agents with NDA-Br obtained using DBI as the brominating agent.

The yields of brominated NDA obtained using DBH and TBCA as brominating agents are compared with the yields of brominated NDA obtained using dibromoisocyanuric acid and NaBr as brominating agents, as shown in the table 4.

As shown, the yields are high using DBH/TBCA method of bromination compared to DBI method of bromination. In particular, the DBH/TBCA method gives good yields for mono bromo NDA compared to NaBr method, whereas yields of mono-bromo NDA using DBI method are not available.

Advantages of DBH as brominating reagent

The present disclosure provides a simple and efficient methodology for the synthesis of mono-, di- and tetrabromo-NDAs for the first time using DBH as brominating reagent. The cost effectiveness of the reagent along with relatively high rate of reaction, the simple procedure, and excellent yields make this a preferred methodology for the synthesis of mono- , di- and tetrabromo-derivatives of DA. Moreover, the methodology or the process of the present disclosure avoids the handling of molecular bromine.

This method of preparation of bromo-NDAs is highly attractive for further construction of diverse functionalized NDIs. The significance of the method worth mentioning include high conversions, mild reaction conditions, simple workup with good to excellent yields and high purity through generally preferred recrystallization and precipitation technique without the need for any further purification steps or procedures. It is found that toluene is a better solvent for the nucleophilic core substitution of bromo-NDIs with «-octylamine. Core substitution with electron donor groups tune the UV-vis absorption and emission properties over a wide visible spectral range compared to minor changes observed with only imide substituted NDIs. This brominating reagent (DBH) and methodology can be easily adopted for the preparation of other brominated derivatives of arylene diimides.

Advantages of TBCA as brominating reagent

TBCA is an efficient brominating reagent for the synthesis of mono-, di- and tetrabromo- NDAs. Although TBCA is not commercially available, its synthetic method is highly facile and use of low cost reagents for its synthesis makes it readily accessible for bromination of NDA. The cost effectiveness of the reagent along with relatively high rate of reaction, the simple procedure, and excellent yields make this a preferred methodology for the synthesis of mono-, di- and tetrabromo-derivatives of NDA. This preparation method for bromination of NDAs is necessary for further construction of diverse functionalized NDIs. The significance of the method worth mentioning include high conversions, mild reaction conditions, simple workup with good to excellent yields and high purity through generally preferred recrystallization technique without the need for any further purification steps or procedures. Core substitution with electron donor groups tune the UV-vis absorption and emission properties over a wide visible spectral range. As a proof of principle, the effect of core substitution with electron donating groups which tune the absorption and emission of NDI over a wide visible spectral range has been demonstrated. This method can be exploited for the bromination of various other aromatic systems.

Claims

We Claim:

1. A process for bromination of arylene dianhydride to obtain brominated arylene dianhydride, said process comprising act of brominating arylene dianhydride with brominating agent selected from 5,5-dimethyl-l,3-dibromohydantoin (DBH) and tribromoisocyanuric acid (TBCA) to obtain brominated arylene dianhydride.

2. The process as claimed in claim 1, wherein the brominated arylene dianhydride is precipitated and recrystallized to obtain pure brominated arylene dianhydride.

3. The process as claimed in claim 1, wherein the arylene dianhydride is 1,4,5,8- naphthal enetetracarb oxy li c di anhy dri de .

4. The process as claimed in claim 1, wherein the arylene dianhyride is dissolved in concentrated acid prior to bromination.

5. The process as claimed in claim 4, wherein the concentrated acid is selected from a group comprising sulphuric acid, oleum and vitriolic acid.

6. The process as claimed in claim 1, wherein the brominating agent and arylene dianhydride are in a ratio ranging from about 0.5: 1 to 3 : 1.

7. The process as claimed in claim 1, wherein the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride, 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride and 2,3,6,7-Tetrabromo-l,4,5,8-naphthalenetetracarboxylic dianhydride.

8. The process as claimed in claim 1, wherein the bromination is carried out at a temperature ranging from about 0 °C to about 80 °C for a time period ranging from about 1 hour to about 16 hours.

9. A one step process for condensation of brominated arylene dianhydride to obtain arylene diimide, said process comprising act of reacting brominated arylene dianhydride with amine to obtain arylene diimide.

10. The process as claimed in claim 9, wherein the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride, 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride and

2.3.6.7- Tetrabromo-l,4,5,8-naphthalenetetracarboxylic dianhydride.

11. The process as claimed in claim 9, wherein the amine is selected from a group comprising n-octylamine , n-butylamine.

12. The process as claimed in claim 9, wherein the process is carried in presence of reagent selected from group comprising dichloromethane, hexane and combination thereof.

13. The process as claimed in claim 9, wherein the arylene diimide is selected from a group comprising N,N'-Bis-(«-octyl)-2-(«-octylamino)-l,4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,6-di(«-octylamino)-l,4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,3,6,7-tetra(«-octylamino)-

1.4.5.8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2-(«-butylamino)- 1,4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2,6-di(«-butylamino)- 1,4,5, 8-naphthalenetetracarboxylic diimide and N,N'-Bis-(«-butyl)-2,3,6,7-tetra(«- butylamino)-l,4,5, 8-naphthalenetetracarboxylic diimide.

14. The process as claimed in claim 9, wherein the condensation is carried out at a temperature ranging from about 0 °C to about 100 °C for a time period ranging from about 1 hour to about 30 hours.

15. The process as claimed in claim 9, wherein the amine and the brominated arylene dianhydride is at a ratio of about 3 : 1.

16. The process as claimed in claim 9, wherein the arylene diimide is purified to obtain purified arylene diimide.

17. The process as claimed in claim 15, wherein the purification is carried out by a process selected from a group comprising chromatography, recrystallization, precipitation and combination thereof.

18. A process for obtaining imide and core substituted arylene diimide from arylene dianhydride, said process comprising acts of:

(a) obtaining brominated arylene dianhydride from arylene dianhydride by the process claimed in claim 1;

(b) reacting the brominated arylene dianhydride with amine to obtain imide substituted arylene diimide; and

19. The process as claimed in claim 18, wherein the arylene dianhydride is 1,4,5,8- naphthal enetetracarb oxy li c di anhy dri de .

20. The process as claimed in claim 18, wherein the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5,8-naphthalenetetracarboxylic dianhydride, 2,6-Dibromo-l,4,5,8-naphthalenetetracarboxylic dianhydride and 2,3,6,7-Tetrabromo-l,4,5,8-naphthalenetetracarboxylic dianhydride.

21. The process as claimed in claim 18, wherein the amine is selected from a group comprising n-octylamine and n-butylamine

22. The process as claimed in claim 18, wherein the steps (b) and (c) are carried in presence of reagent selected from a group comprising acetic acid, formic acid, methanol, phosphorus tribromide, toluene, water, sodium sulphate, dimethyl formamide, dichloromethane, hexane and combination thereof.

23. The process as claimed in claim 18, wherein the amine and the brominated arylene dianhydride is at a ratio of about 3 : 1.

24. The process as claimed in claim 18, wherein the imide substituted arylene diimide is selected from a group comprising N,N'-Bis(«-octyl)-2-bromo-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N-Bis(«-octyl)-2,6-dibromo-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis(«-octyl)-2,3,6,7-tetrabromo-l, 4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis(«-butyl)-2-bromo- 1 ,4,5,8- naphthalenetetracarboxylic diimide, N,N'-Bis(«-butyl)-2,6-dibromo-l,4,5,8- naphthalenetetracarboxylic diimide and N,N'-Bis(«-butyl)-2,3,6,7-dibromo-l, 4,5,8- naphthal enetetracarb oxy li c diimi de .

25. The process as claimed in claim 18, wherein the amine and imide substituted arylene dianhydride is at a ratio ranging from about 1 : 1 to about 5: 1.

26. The process as claimed in claim 18, wherein the imide and core substituted arylene diimide is selected from a group comprising N,N'-Bis-(«-octyl)-2-(«-octylamino)- 1,4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,6-di(«-octylamino)- 1,4,5, 8-naphthalenetetracarboxylic diimide, N,N-Bis-(«-octyl)-2,3,6,7-tetra(«- octylamino)-l, 4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2-(«- butylamino)-l,4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2,6-di(«- butylamino)-l,4,5, 8-naphthalenetetracarboxylic diimide and N,N'-Bis-(«-butyl)- 2,3, 6,7-tetra(«-butylamino)-l,4,5, 8-naphthalenetetracarboxylic diimide.

27. A process for obtaining imide and core substituted arylene diimide from arylene dianhydride, said process comprising acts of:

28. The process as claimed in claim 27, wherein the arylene dianhydride is 1,4,5,8- naphthal enetetracarb oxy li c di anhy dri de .

29. The process as claimed in claim 27, wherein the brominated arylene dianhydride is selected from a group comprising 2-Bromo-l,4,5, 8-naphthalenetetracarboxylic dianhydride, 2,6-Dibromo-l, 4,5, 8-naphthalenetetracarboxylic dianhydride and

2.3.6.7- Tetrabromo-l, 4,5, 8-naphthalenetetracarboxylic dianhydride.

30. The process as claimed in claim 27, wherein the amine is selected from a group comprising n-octylamine and n-butylamine.

31. The process as claimed in claim 27, wherein the step (b) is carried in presence of reagent selected from a group comprising dichloromethane, hexane and combination thereof.

32. The process as claimed in claim 27, wherein the imide and core substituted arylene diimide is selected from a group comprising N,N'-Bis-(«-butyl)-2-(«-butylamino)-

1.4.5.8- naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2,6-di(«-butylamino)- 1,4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-butyl)-2,3,6,7-tetra(«- butylamino)-l,4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2-(«- octylamino)-l, 4,5, 8-naphthalenetetracarboxylic diimide, N,N'-Bis-(«-octyl)-2,6-di(«- octylamino)-l, 4,5, 8-naphthalenetetracarboxylic diimide and N,N'-Bis-(«-butyl)- 2,3, 6,7-tetra(«-butylamino)-l,4,5, 8-naphthalenetetracarboxylic diimide .

33. Use of 5,5-dimethyl-l,3-dibromohydantoin as brominating agent for brominating arylene dianhydrides.

34. Use of tribromoisocyanuric acid as brominating agent for brominating arylene dianhydride .

35. The use as claimed in claims 33 and 34, wherein the arylene dianhydride is naphthalene dianhydride.