WO2016162810A1

WO2016162810A1 - Luminescent conjugated microporous polymer with lewis acidic 'boron' sites on the pore surface: ratiometric sensing and capture of f' ion

Info

Publication number: WO2016162810A1
Application number: PCT/IB2016/051961
Authority: WO
Inventors: Venkata SURESH M.; Arkamita BANDYOPADHYAY; Swapan K. PATI; Tapas Kumar MAJI
Original assignee: Jawaharlal Nehru Centre For Advanced Scientific Research
Priority date: 2015-04-09
Filing date: 2016-04-07
Publication date: 2016-10-13

Abstract

The present invention relates to an electron deficient boron based conjugated microporous polymers (BCMP) comprising a boron appended triarylborane porous conjugated microporous polymers solid adsorbents, featuring triarylborane having Lewis acidic boron centers separated by organic linkers as integral part of polymeric network. The present invention also relates to a process for the preparation of electron deficient boron based conjugated microporous polymers. The present invention also provides a process for detection of fluoride in water or in substance which contains fluoride by using BCMP.

Description

Luminescent Conjugated Microporous Polymer with Lewis Acidic 'Boron' Sites on the Pore Surface: Ratiometric Sensing and Capture of F^"

Ion

Field of the invention

The present invention relates to an electron deficient boron based conjugated microporous polymer (BCMP)comprising a boron appended triarylborane porous conjugated microporous polymers solid adsorbents, featuring triarylborane having Lewis acidic boron centers separated by organic linkers as integral part of polymeric network, which has potential for selective detection of small anions (F^~) at solid/liquid interface. The present invention provides a rational approach and synthesis of a luminescent BCMP for capture and selective turn-on fluorescent sensing of F^" ion in aqueous medium with a detection limit 2.6 .

Background of the invention

Fluoride ion or fluorine containing drug molecules are biologically important and its deficiency is known to cause dental fluorosis and osteoporosis. However, excess intake of fluoride show adverse effects on human health. Fluoride is known to interfere with growth of brain and develop neurotoxicity and aluminium fluoride complexes found in drinking water causes morphological changes to kidneys and are known to associate with Alzheimers disease (P. Adler, Fluorides and health, World Health Organization, Geneva, 1970). Therefore, selective detection of fluoride ion is of high significance in the current research. Water fluoridation is a common practice, where in the fluoride is added to water in order to reduce the dental health effects. However, it is impossible to control the dose of each individual due to their different consumption of drinking water in a day. Moreover, fluoridated water is used for food processing such as beverages, tea and dental products. Therefore, removal of F^" ion from drinking water is an important element to be considered, nevertheless, methods such as reverse osmosis, ion-exchange, membrane process and adsorption have been demonstrated for defluoridation of drinking water, they have several drawbacks such as less selectivity or leaching problems (S. Jagtap,M. K. Yenkie,N. Labhsetwar,S. Rayalu, Chem. Rev. 2012, 112, 2454-2466; and B. Pan,J. Xu,B. Wu,Z. Li,X. Liu, Environ. Sci. Technol. 2013, 47, 9347-9354). The selective sequestration of F^" ion at heterogeneous phase using insoluble porous solids is one of the promising strategies. There are very few reports on organic-inorganic hybrid porous solids (metal-organic frameworks, MOFs) for the capture of F^" ion in water, however, the selectivity or signal response is relatively poor (N. N. Adarsh,A. Grelard,E. J. Dufourc,P. Dastidar, Cryst. Growth Des. 2012, 12, 3369-3373; and B. Chen,L. Wang,F. Zapata,G. Qian,E. B. Lobkovsky, J. Am. Chem. Soc. 2008, 130, 6718-6719). So the development of new porous and robust materials is an urgent need for selective recognition and sequestration of F^" ion at very low concentration. World health organization recommends F^" ion content in drinking water to be lower than 1.5 ppm and higher amounts than this causes serious health hazards (P. Adler, Fluorides and health, World Health Organization, Geneva, 1970). Early efforts based on non-covalent interactions such as H-bonding, cationic receptors have been reported for sensing F^" ion in both organic solvents and water (M. S. Han, D. H. Kim, Angew. Chem. Int. Ed. 2002, 41, 3809-3811; P. Ashok kumar, H. WeiBhoff, W. Kraus,K. Rurack, Angew. Chem. Int. Ed. 2014, 53, 2225-2229; C. Saravanan, S. Easwaramoorthi,L. Wang, Dalton Trans. 2014, 43, 5151-5157; and T. Mizuno, W.-H. Wei, L. R. Eller, J. L. Sessler, J. Am. Chem. Soc. 2002, 124, 1134-1135). However, most of the receptors have drawbacks due to the non-selective electrostatic forces with other anions or irreversibility or slow response. Small molecule sensors based on napthalenediimides and boronic acid polymer relying on anion-π interactions or Lewis acid-base interactions have been demonstrated as colorimetric sensors for the detection of F ion (S. Guha, S. Saha, . Am. Chem. Soc. 2010, 132, 17674- 17677; M.-S. Yuan, Q. Wang, W. Wang, D.-E. Wang, J. Wang, J. Wang, Analyst 2014, 139, 1541-1549; H. Li, R. A. Lalancette, F. Jaekle, Chem. Commun. 2011, 47, 9378-9380; and X. Y. Liu, D. R. Bai, S. Wang, Angew. Chem. Int. Ed. 2006, 45, 5475-5478). However, their regeneration from aqueous solutions, require tedious extraction methods or incompatible under aqueous conditions. On the other hand, sensors based on metal-coordination interactions such as lanthanide complexes or MOFs have been developed, nevertheless, reversibility or their regeneration leads to disintegration of the framework structure (T. Liu, A. Nonat, M. Beyler, M. Regueiro-Figueroa, K. Nchimi Nono, O. Jeannin, F. Camerel, F. Debaene, S. Cianferani-Sanglier, R. Tripier, C. Platas-Iglesias, L. J. Charbonniere, Angew. Chem. Int. Ed. 2014, 53, 7256-7263; A. B. Descalzo, D. Jimenez, J. El Haskouri, D. Beltran, P. Amoros, M. D. Marcos, R. Martinez-Manez, J. Soto, Chem. Commun. 2002, 562-563.; F. M. Hinterholzinger, B. Riihle, S. Wuttke, K. Karaghiosoff, T. Bein, Sci. Rep. 2013, 3, 2562; and H. Sohn, S. Letant, M. J. Sailor, W. C. Trogler, J. Am. Chem. Soc. 2000, 122, 5399- 5400). Anion recognition units containing Lewis acidic boron centers remain an attractive and rarely explored strategy. Boron center with sp hybridized trigonal planar structure and empty ρ_π orbital perpendicular to it dominates receptor chemistry of boron (Z. M. Hudson, S. Wang, Acc. Chem. Res. 2009, 42, 1584-1596). Electron rich nucleophiles or anions able to interact with boron center through Lewis acid-base interactions. Triarylboranes with substituted methyl groups at ortho position have been reported as stable and selective turn- on or off sensors for fluoride ion in presence of other anions (F. Jakle, Chem. Rev. 2010, 110, 3985-4022; and C. R. Wade, A. E. J. Broomsgrove, S. Aldridge, F. P. Gabbai, Chem. Rev. 2010, 110, 3958-3984). In this context, conjugated microporous polymers with triarylborane units as integral part of the polymer network would be superior for the selective detection of fluoride anion. Large density of e^" deficient boron centers will help in rapid response and heterogeneity in phase will facilitate easy recovery of sample by simple centrifugation. Further, permanent porosity of CMP would help to capture and removal of F^" from the aqueous solution.

Conjugated microporous polymers (CMPs) continue to attract tremendous attention among the porous organic materials due to their extended π-conjugation combined with microporous nature (pore size < 2nm) (Y. Xu, S. Jin, H. Xu, A. Nagai, D. Jiang, Chem. Soc. Rev. 2013, 42, 8012-8031; and A. I. Cooper, Adv. Mater. 2009, 21, 1291-1295). The pronounced chemical/thermal stability through covalent linkages can for example facilitate easy functionalization of pore surface for desired properties such as catalysis, gas storage or separation. Furthermore, the ability of CMPs to host various guests at confined environment of nanopores offer optical, electronic or sensory properties (F. Vilela, K. Zhang, M. Antonietti, Energy Environ. Sci. 2012, 5, 7819-7832; J.-X. Jiang, A. Trewin, D. J. Adams, A. I. Cooper, Chem. Sci. 2011, 2, 1777-1781; L. Chen, Y. Honsho, S. Seki, D. Jiang, J. Am. Chem. Soc. 2010, 132, 6742-6748; X. Liu, Y. Xu, D. Jiang, J. Am. Chem. Soc. 2012, 134, 8738-8741; Y. Xu, L. Chen, Z. Guo, A. Nagai, D. Jiang, J. Am. Chem. Soc. 2011, 133, 17622-17625; J. Brandt, J. Schmidt, A. Thomas, J. D. Epping, J. Weber, Polym. Chem. 2011, 2, 1950-1952; and Y. Xu, L. Chen, Z. Guo, A. Nagai, D. Jiang, J. Am. Chem. Soc. 2011, 133, 17622-17625). Confining exclusively small analyte molecules in the micropores and selective host-guest interactions with chromophoric pore walls trigger unique changes in fluorescent signal (either turn-off or turn-on) which is critical in optical sensors (X. Liu, Y. Xu, D. Jiang, J. Am. Chem. Soc. 2012, 134, 8738-8741; Y. Cui, Y. Yue, G. Qian, B. Chen, Chem. Rev. 2012, 112, 1126-1162). Among the CMPs, heteroatom containing porous polymers represent a special class of polymers, which tend to show characteristic photophysical and electronic behaviour (X. Liu, Y. Zhang, H. Li, A. Sigen, H. Xia, Y. Mu, RSC Adv. 2013, 3, 21267-21270). In this respect, conjugated triarylborane polymers are of special interest, where the electron donor atoms such as N, C are replaced by Lewis acidic B centers (N. Matsumi, Y. Chujo, Polym. J. 2007, 40, 77-89; W.-M. Wan, F. Cheng, F. Jakle, Angew. Chem. Int. Ed. 2014, 53, 1-6; and P. Chen, F. Jakle, J. Am. Chem. Soc. 2011, 133, 20142-20145). Such Lewis acidic conjugated polymers could be beneficial for selective detection of anions at solid/liquid interface in confined nanospaces.

Early efforts based on non-covalent interactions such as H-bonding, anion-π interactions, metal-anion coordination interactions, cationic receptors have been reported for sensing F^" ion in both organic solvents and water. However, most of the receptors have drawbacks due to the non-selective electrostatic forces with other anions or irreversibility or slow response. Small molecule sensors based on naphthalenediimides and polymer comprising boronic acid relies on anion-π interactions or Lewis acid-base interactions have been demonstrated as colorimetric sensors for the detection of F^" ion. However, their regeneration from aqueous solutions requires tedious extraction methods or incompatible under aqueous conditions. On the other hand, sensors based on metal-coordination interactions such as lanthanide complexes or metal-organic frameworks (MOFs) have been developed, nevertheless, reversibility of inorganic complexes is difficult or cannot be recyclable due to the structural disintegration on fluoride binding to the metal centers.

Summary of the Invention

Accordingly the present invention provides an electron deficient boron based conjugated microporous polymers (BCMP) comprising a polymeric network of triarylborane and an organic linkers wherein the triarylborane is attached with the organic linkers. The BCMP showed excellent fluoride sensing and capture properties.

In an embodiment of the present invention, the electron deficient boron based conjugated microporous polymers (BCMP) comprising a boron appended triarylborane porous conjugated microporous polymers solid adsorbents, featuring triarylborane having Lewis acidic boron centers separated by organic linkers as integral part of polymeric network.

In one embodiment of the present invention, the triarylborane is selected from the group comprising of:

In another embodiment of the present invention, the organic linker is selected from the group comprising of:

The present invention also provides a process for the preparation of electron deficient boron based conjugated microporous polymers, wherein said process comprising coupling reaction between a triarylborane moiety and the organic linker in presence of a solvent and a coupling catalyst. In one embodiment of the present invention, the solvent used is selected from a group comprising of dry DMF and Et₃N; THF and Toluene.

In another embodiment of the present invention, the coupling catalyst used is selected from a group comprising of dry mixture Pd(PPh₃)₄ and Cul, Pd(PPh₃)₂Cl₂, Pd(dppe)Cl, Pd(dppe)Cl₂ and Pd(dppf)Cl₂.

In yet another embodiment of the present invention, the triarylborane moiety is used in the range of 5 % to 20 % volume percentage.

In yet another embodiment of the present invention, the organic linker is used in the range of 30 % to 50 % volume percentage.

In yet another embodiment of the present invention, the triarylborane moiety and the organic linker are dissolved in the solvent at a temperature in the range of 25 to 30 °C.

In yet another embodiment of the present invention, the coupling catalyst is added to the reaction mixture at a temperature in the range of 25 to 30 °C.

In yet another embodiment of the present invention, the triarylborane moiety is a halogenated triarylborane.

The present invention provides an electron deficient boron based conjugated microporous polymer (BCMP) having IUPAC name poly(tris(2,3,5,6-tetramethyl) boron - alt-(4,4'-diethynylbiphenylene) and the structure:

In yet another embodiment of the present invention, the boron conjugated microporous polymers is three dimensional infinite porous polymer, and the value of 'n' is up to infinite. In one of the preferred embodiment the value of 'n' is up to 64.

The present invention provides a process for the preparation of electron deficient boron based conjugated microporous polymers having IUPAC name poly(tris(2,3,5,6- tetramethyl) boron -alt-(4,4'-diethynylbiphenylene), wherein said process comprising the steps of:

a) dissolving tris(4-bromo-2,3,5,6-tetramethylphenyl)boron and 4,4'- diethynylbiphenyl is in a solvent to obtain a reaction mixture; and

b) adding a coupling catalyst to the reaction mixture to obtain the boron based conjugated microporous polymers.

In an embodiment of the invention, the solvent used in step (a) is selected from a group comprising of dry DMF and Et₃N; THF and Toluene.

In another embodiment of the invention, the coupling catalyst used in step (b) is selected from a group comprising of dry mixture Pd(PPh₃)₄ and Cul, Pd(PPh₃)₂Cl₂, Pd(dppe)Cl, Pd(dppe)Cl₂ and Pd(dppf)Cl₂.

In yet another embodiment of the invention, the tris(4-bromo-2,3,5,6- tetramethylphenyl)boron is used in the range of 5 % to 20 % volume percentage.

In yet another embodiment of the invention, the 4,4'-diethynylbiphenyl is used in the range of 30 % to 50 % volume percentage.

In one of the embodiment of the invention, the tris(4-bromo-2,3,5,6- tetramethylphenyl)boron and 4,4'-diethynylbiphenyl is dissolved in the solvent at a temperature in the range of 25 to 30 °C.

In one of the embodiment of the invention, the coupling catalyst is added to the reaction mixture at a temperature in the range of 25 to 30 °C.

The present invention provides a process for detection of fluoride in a substance which contains fluoride comprising:

dispersing a boron based conjugated microporous polymer (BCMP) in an organic- aqueous solvent mixture to obtain a dispersion; and

incrementally adding solution of substance which contains fluoride in the dispersion to obtain a blue emission, wherein the blue emission confirm the presence of fluoride in the substance.

In an embodiment of the invention, the organic-aqueous solvent mixture is selected from the group comprising DMSO and H₂0, THF and H₂0, and DMF and H₂0. In an embodiment of the invention, the volume percentage ratio of organic-aqueous solvent is in the range of 7-10 : 0.5-3.

In another embodiment of the invention, the volume percentage ratio of DMSO/H₂0 is 8:2.

In yet another embodiment of the invention, the volume percentage ratio of

THF/H₂0 is 9: 1.

In one of the embodiment of the invention, the BCMP shows selective turn-on blue emission for F^" ion in aqueous mixtures with a detectable limit of 2.6 .

Brief Description of Figures

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying figures in which like characters represent like parts throughout the figures, wherein:

Figure 1 illustrates 1H-NMR spectrum of in^'s(4-bromo-2,3,5,6-tetramethylphenyl) boron in CDC1₃.

Figure 2 illustrates 1H-NMR spectrum of 4,4'-diethynylbiphenyl in CDCI₃.

Figure 3 illustrates Synthetic scheme of BCMP using the C-C coupling strategy between ins(4-bromo-2,3,5,6-tetramethylphenyl) boron and 4,4'-diethynylbiphenyl.

Figure 4 illustrates FTIR spectrum of Soxhelet extracted BCMP.

Figure 5 illustrates ¹³C-CP/MAS solid state NMR spectrum of BCMP showing the formation of the polymer through C-C linkage.

Figure 6 illustrates XPS transition spectra of BCMP; left: transition of Br 3/?3/2 and B is, right: transition of Cls.

Figure 7 illustrates Powder X-ray diffraction pattern of BCMP after soxhelet extraction in the range of 5-50° collected using CuKa radiation.

Figure 8 illustrates Electron microscopy images of BCMP, (a) FESEM image showing the clustered spherical particles and (b) corresponding TEM.

Figure 9 illustrates TEM of BCMP at higher magnifications and inset shows ED pattern. Figure 10 illustrates TGA profile of as-synthesized BCMP in the range of 30-1000 °C with a heating rate of 5 °C/min.

Figure 11 illustrates Adsorption isotherms of BCMP (a) N₂ adsorption at 77 K (Inset; pore size distribution diagram of BCMP) and (b) C0₂ adsorption profile at 195 K.

Figure 12 illustrates Adsorption isotherms of BCMP: C0₂ adsorption profile at 273 K. Figure 13 illustrates (a) UV/Vis absorption (b) corresponding emission (open circles) and excitation (filled circles) spectra of BCMP in solid state.

Figure 14 illustrates Solvent polarity dependent emission spectra of BCMP (a) emission changes in non-polar solvent hexane to highly polar solvent like water and (b) changes in emission spectra in presence of polar coordinating solvents.

Figure 15 illustrates (a) HOMO-LUMO energy level diagram of ins(2,3,5,6-tetramethyl-4- bromophenyl) boron and smallest unit of BCMP. (b) Electrostatic potential plots of smallest unit of BCMP after F^" binding (red and blue regions indicate high and low e^" density respectively), (c) Energy minimized structure of F^"@BCMP showing the changes in bonding environment around boron center. Red: B, Blue: C, Green: F, Silver: H

Figure 16 illustrates (a) UV/Vis absorption spectra of monomer unit of BCMP in gas phase and different solvents (TD-DFT calculations) and (b) excitation spectra of BCMP in different solvent collected at 520 nm.

Figure 17 illustrates Changes in fluorescence spectrum of BCMP on incremental addition of F^" ion in THF solution.

Figure 18 illustrates Emission of the extended modified linker at 410 nm.

Figure 19 illustrates Orbital plots of modified extended diethynylbiphenyl linker showing the S 1 to SO transition.

Figure 20 illustrates Images of BCMP under UV lamp before and after addition of TBAF in THF.

Figure 21 illustrates Electrostatic potential maps of fluoride bound monomer unit of BCMP (a) e^" density around boron and (b) e^" density around fluoride complexed to boron. Red regions indicate high e^" density and blue regions indicate low e^" density on scale.

Figure 22 illustrates Energy minimized structure of fluoride bound monomer unit of BCMP showing the geometry of boron center on fluoride complexation.

Figure 23 illustrates Changes in emission spectra of BCMP dispersed in water on incremental addition of TBAF.

Figure 24 illustrates Changes in fluorescence spectrum of BCMP on incremental addition of F^" ion in (a) DMSO/H₂0 (8:2) mixture and (b) in THF/H₂0 (9: 1) mixture (Inset; Images of BCMP dispersed in THF/H₂0 under UV light before and after F^" addition and its reversibility).

Figure 25 illustrates Stern- Volmer Plot of I/I₀ (λ_6Π1 = 520 nm) vs [F] (Intial concentration of [F] = 4. 5 x 10^"4 M, THF:H₂0 (9: 1)). Figure 26 illustrates Spectral changes of BCMP emission on addition of 50 /L of F^" ion (final concentration, < 2.6 μΜ) after 15 min.

Figure 27 illustrates Plot of (l-I/Io)/[F] vs Vh of BCMP fluorescence titration data.

Figure 28 illustrates Changes in fluorescence spectrum of BCMP on addition (100 L) of anions such as CI^", Br^", I^", C0₃ ^2", S0₄ ^2" , N0₃ ^" and F^" in THF/H₂0 (9: 1). 10 mg of each salt is dissolved in 2 mL of THF/H₂0 (9: 1) mixture.

Figure 29 illustrates Comparison of emission spectrum of BCMP and recycled BCMP after sensing of F^" ion (a) recycled from THF/H₂0 mixture and (b) recycled from DMSO/H₂0 mixture, (c) Images of BCMP dispersion on addition of excess water to F^"@BCMP under UV lamp.

Figure 30 illustrates ¹⁹F-NMR spectra of tetrabutylammonium fluoride (TBAF) solution in dmso-i/⁵ ^ mM) (a) before and (b) after 60 sec and (c) after 120 sec of soaking with BCMP (Trifluorotoluene as standard reference). Inset: Change of emission color of BCMP dispersion to blue after 120 sec under UV lamp.

Figure 31 illustrates ¹H- MR spectrum of trifluorotoluene (peaks indicated by '*') and tetrabutylammonium fluoride (TBAF) (peaks indicated by 'δ') in dmso-J⁶.

Figure 32 illustrates 1H-NMR spectrum of trifluorotoluene and tetrabutylammonium fluoride in dmso-J⁶ (a) before (stock), (b) after 60 sec and (c) after 120 sec of soaking with BCMP. ('*' peaks of trifluorotoluene and 'δ' peaks of tetrabutylammonium cation and other peaks represent dmso-i/⁵).

Figure 33 illustrates ED AX analysis showing the elements of (a) BCMP, (b) F^"@BCMP and (c), (d) elemental mapping of F^"@BCMP showing uniform distribution of F^" throughout the polymer matrix.

Figure 34 illustrates Fluorescence response of BCMP on addition of incremental amounts of solution obtained from Colgate anticavity toothpaste extract.

Detailed Description of the invention

While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the scope of the invention as defined by the appended claims. The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention.

Definition:

For the purposes of this invention, the following terms will have the meaning as specified therein:

Conjugated microporous polymers (CMPs) used herein are infinite three dimensional porous polymers formed by the cross linking of small molecule precursors through C-C cross coupling reaction. CMPs contain specified pore size and surface area as like Zeolites and metal-organic frameworks (MOFs) which are accessible by small gas molecules like N₂. They possess similar properties like conjugated polymers such as conductivity, mechanical rigidity and insolubility.

Solid adsorbents used herein are porous solid materials like porous carbon, zeolites, silica and metal-organic frameworks that can adsorb small molecules, ions etc. from their solutions or from gas mixtures.

Confined pore size used herein means small pores (pore diameter «1 nm) surrounded by organic nodes and linkers.

Small anions used herein means anions with relatively small ionic radius such as F^" and CN^~.

Large anions used herein means anions with relatively larger ionic radius such as CI^" and Γ.

Solid/liquid interface used herein is an interface between solid phase and a liquid phase wherein the transfer of ions occurs from one phase to other phase reversibly. In the present case BCMP polymer is referred to be solid phase since it is insoluble and solution containing F^" ions is referred to be liquid phase.

Chemical stability used herein refers to non-degradation of compound in water or other chemical conditions and thermal stability refers to no decomposition of compound on heating at high temperatures. BCMP is stable under aqueous conditions and it has high thermal stability up to 350 °C. Metal-organic frameworks (MOFs) used herein are class of crystalline porous materials formed by the assembly of metal ions or metal clusters and bridging polydentate organic ligands. They are three dimensional and possess long range structure periodicity.

Strong intramolecular charge transfer (ICT) used herein refers to the transfer of charge or electron from donor to acceptor moiety intramolecularly where the donor and acceptor are connected through bond. When the strength of the donor-acceptor pair is strong it shows strong intramolecular charge transfer (ICT) property.

Organic-aqueous solvent mixture used herein is mixture of organic solvent and water by volume percentage in a defined ratio, for example DMSO/H₂0 (1:1) mixture.

The present invention relates to an electron deficient boron based conjugated microporous polymers. More particularly, the present invention provides a boron appended triarylborane porous CMP solid adsorbents, featuring high density of Lewis acidic boron centers separated by organic linkers as integral part of polymeric network which are highly beneficial and unprecedented for the detection of F^" ion. Confined pore size may exclusively allow the diffusion of small anions over larger ones. Detection of anions at solid/liquid interface facilitates easy recovery of compound by centrifugation and covalent linkages give excellent chemical/thermal stability, unlike metal-organic frameworks (MOFs). The present invention provides a rational approach and unprecedented boron conjugated microporous polymer (BCMP) constituting triarylborane as integral part of polymer for selective sequestration and turn-on fluorescent sensing of F^" ion in aqueous solutions. BCMP shows strong intramolecular charge transfer (ICT) emission due to the presence of π-conjugated organic linker and empty ρ_π orbital of boron. However, binding of F^" ion to boron center makes it e^" rich and restricts the charger transfer and activates the localized blue emission from linker. Turn-on fluorescent sensing of F^" ion at solid-liquid interface of conjugated microporous polymer nanopores is unprecedented.

The present invention relates reversible and selective capture/detection of F^" ion in water which is utmost important as excess intake of fluoride shows adverse effects on human health. Highly robust Lewis acidic luminescent porous organic materials would be potential for efficient sequestration and detection of F^" ion. Here in, we delineate rational approach and synthesis of a boron based Lewis acidic conjugated microporous polymer (BCMP) derived from tra(4-bromo-2,3,5,6-tetramethylphenyl)boron and diethynylbiphenyl linker with a pore size of 1.08 nm for selective turn-on sensing and capture of F^" ion. Presence of vacant p_n orbital on boron center of BCMP results intramolecular charge transfer (ICT) from linker to boron. BCMP shows selective turn- on blue emission for F^" ion in aqueous mixtures with a detectable limit of 2.6 μΜ. Strong B-F interactions facilitate rapid sequestration of F^" by BCMP. ICT emission of BCMP can be reversibly regenerated by addition of excess water and polymer can be reused for several times.

The following non-limiting examples illustrate in details about the invention. However, they are, not intended to be limiting the scope of present invention in any way.

Starting materials used for the synthesis of precursors of BCMP were purchased from Sigma Aldrich co. Ltd and used as received. All the precursors required for the synthesis of BCMP were prepared according to literature reports. All the reactions were performed under inert conditions of N₂ atmosphere using dry solvent unless specified.

Example 1

Synthesis of l,4-dibromo-2,3,5, 6-tetramethylbenzene

1,2,4,5-tetramethylbenzene (2 g, 14.9 mmol) is dissolved in dry dichloromethane (10 mL) and cooled to 0° C. Then, Br₂ (14.9 mmol, 0.7 mL) is added dropwise at 0° C under continuous stirring and N₂ atmosphere. The reaction mixtures bring to room temperature and stirred for further 10 hrs. The excess Br₂ is quenched with sodium thiosulphate and extracted with dichloromethane. Purified using column chromatography with hexane as eluent. Yield: 70 %.

Example 2

Synthesis of tris(4-bromo-2,3,5,6-tetramethylphenyl) boron

l,4-dibromo-2,3,5, 6-tetramethylbenzene (lg, 3.42 mmol) is dissolved in dry diethylether and pentane solution of n-BuLi (2.5 M, 3.4 mmol, 1.4 mL) is added at -78° C under inert atmosphere. Reaction mixture is allowed to warm to 0° C and stirred for 20 min, then BF₃.Et₂0 (1.1 mmol, 0.14 mL) is added dropwise at -78° C. The reaction mixture is warmed to room temperature and then stirred for further 16 hrs. An excess amount of water is added to the reaction mixture that resulted a white precipitate. The precipitates were collected by filtration and the filtrate is extracted with ether over dried over sodium sulfate. The solids were washed with ether and methanol to obtain pure product. Yield: (65 %). Example 3

Synthesis of 4,4'-bis( -trimethylsilylpropynyl)biphenyl

4,4'-diiodobiphenyl (2g, 4.92 mmol) and Et N (40 mL) is dissolved in THF and degassed using three free-thaw pump cycles followed by Ar purging. Then, PdCl₂(PPh₃)₂ (0.24 mmol, 140 mg), Cul (0.24 mmol, 38 mg) and trimethylsilylacetylene (19.7 mmol, 2.8 mL) is added under inert atmosphere. The reaction mixture is degassed/purged with Ar and refluxed for 10 hrs at room temperature. Then the reaction mixture is filtered and washed with hexane several times, the filtrate is dried under reduced pressure. Mixture is purified by coloumn chromatography using hexane/ethylacetate (5 %). Compound obtained as grey crystalline powder. Yield: 60 %.

Example 4

Synthesis of 4,4'-diethynylbiphenyl

4,4'-bis(-trimethylsilylpropynyl)biphenyl (lg, 2.89 mmol) is dissolved in methanol/dichloromethane mixture (1: 1, 50 mL) and K₂CO₃ (1.6 g, 11.5 mmol) is added and stirred for 6 hrs at room temperature. Reaction mixture is added to water to dissolve unreacted K₂CO₃ and extracted with dichloromethane. The DCM solution is dried under reduced pressure to result in pale yellow powder. Yield: 80%.

Example 5

Synthesis ofBCMP

tris(4-bromo-2,3,5,6-tetramethylphenyl)boron (120 mg, 0.18 mmol) and 4,4'- diethynylbiphenyl (60 mg, 0.29 mmol) is dissolved in dry DMF ( 5 mL) and Et₃N (1.5 mL) and degassed using freeze-thaw pump cycles. To the reaction mixture Pd(PPh₃)₄ (36 mg, 0.03 mmol), Cul (12 mg, 0.063 mmol) is added under N₂ atmosphere followed by refluxing at 140 °C for 24 hrs. The precipitates formed are filtered and washed several times with THF and ethanol. Further purification was done using Soxhelet extraction with THF and MeOH for 24 hrs each. Yield: 60 % (0.3-0.5 mol% of Pd is found from ED AX analysis). Structural characterization ofBCMP

BCMP is synthesized by Sonogashira C-C coupling strategy catalyzed by Pd(0)/Cul between /rzs(4-bromo-2,3,5,6-tetramethylphenyl)boron node (Figure 1) and 4,4'- diethynylbiphenyl linker (Figure 2) as shown in Figure 3.

The polymer formed is purified by soxhelet extraction with tetrahydrofuran (THF) and methanol (MeOH). Fourier transform infrared spectroscopy (FTIR) of BCMP show bands at 1095 cm^"1, 1600 cm^"1 and 2100 cm^"1 corresponding to the stretching vibrations of v(C-B), v(C=C) and v(C≡C) respectively (Figure 4), confirms presence of both node and linker moieties in the polymer (A. P. Cote, A. I. Benin, N. W. Ockwig, M. O'Keeffe, A. J. Matzger, O. M. Yaghi, Science 2005, 310, 1166-1170 and R. Dawson, A. Laybourn, Y. Z. Khimyak, D. J. Adams, A. I. Cooper, Macromolecules 2010, 43, 8524-8530).

Formation of polymer is unequivocally confirmed by solid state 13 C-CP/MAS

NMR, Figure 5 shows moderate signal at 90 ppm assigned to 'C of triple bond, suggesting bonding of triarylborane node and 4, 4'-diethynylbiphenyl linker. Other peaks ranging from 120-150 ppm can be assigned to the aromatic carbon of phenyl rings. And, peak at 19 ppm is assigned to aliphatic methyl substituents of the phenyl rings (J.-X. Jiang, F. Su, A. Trewin, C. D. Wood, H. Niu, J. T. A. Jones, Y. Z.

Khimyak, A. I. Cooper, J. Am. Chem. Soc. 2008, 130, 7710-7720 and J.-X. Jiang, A. Trewin, F. Su, C. D. Wood, H. Niu, J. T. A. Jones, Y. Z. Khimyak, A. I. Cooper,

Macromolecules 2009, 42, 2658-2666).

Presence of boron in BCMP is confirmed from X-ray photoelectron spectroscopy (XPS) analysis, Figure 6 shows B is peak centered at 189.90 eV corresponds to boron and peak at 184.45 eV corresponds to Br3/?_3/2 suggest presence of boron and free terminal bromine of triarylborane node in BCMP (C. Ronning, D.

Schwen, S. Eyhusen, U. Vetter, H. Hofsass, Surf. Coat. Technol. 2002, 158, 382-387; L.

Ci, L. Song, C. Jin, D. Jariwala, D. Wu, Y. Li, A. Srivastava, Z. F. Wang, K. Storr, L.

Balicas, F. Liu, P. M. Ajayan, Nat. Mater. 2010, 9, 430-435 and A. F. Lee, Z. Chang, S.

F. J. Hackett, A. D. Newman, K. Wilson, J. Phys. Chem. 2007, 111, 10455-10460). Powder X-ray diffraction (PXRD) measurement shows a broad peak at 28° indicating amorphous nature of BCMP (Figure 7).

Scanning electron microscope (SEM) images show formation of clustered spherical particles of size varies from 100-300 nm (Figure 8a). Similarly, transmission electron microscopy (TEM) measurements reveal the presence of clustered particles (Figure 8b); however at higher magnifications TEM reveals presence of micropores in the particle (Figure 9).

Thermogravimetric analysis (TGA) of BCMP shows no appreciable weight loss up to 280 °C and further heating results in steady weight loss (50 %) till 720 °C (Figure 10) and a constant mass is observed till 1000 °C. These results suggest the absence of any traces of catalyst Pd(PPh₃)₄, the remaining mas may be attributed to the presence of oxides of boron and Pd(0) nanoparticles. Such mass constancy is also observed in covalent organic frameworks and metal-organic frameworks (A. P. Cote, A. I. Benin, N. W. Ockwig, M. O'Keeffe, A. J. Matzger, O. M. Yaghi, Science 2005, 310, 1166-1170 and E. L. Spitler, B . T. Koo, J. L. Novotney, J. W. Colson, F. J. Uribe-Romo, G. D. Gutierrez, P. Clancy, W. R. Dichtel, J. Am. Chem. Soc. 2011, 133, 19416- 19421).

N₂ adsorption measurement at 77 K shows type-I adsorption profile with an appreciable uptake in lower pressure regions, and the final uptake amount is found to be 207 mL/g (Figure 11). Application of Brunauer-Emmet-Teller (BET) model to the N₂ isotherm in the range of 0.01-0.3 P/PQ yielded a surface area of 390 m /g. Also, Non-local density functional theory (NL-DFT) model fitted to N₂ adsorption isotherm that gives an average pore size of 1.08 nm thereby signifying microporous nature of the polymer (Figure 11 ; inset). BCMP further shows C0₂ uptake capacity of 90 mL (18 wt%) at 195 K upto 1 atm (Figure 1 lb) and 60 mL(12 wt%) at 273 K upto 30 bar (Figure 12).

Photophysical Studies

BCMP appears as dark green colored compound in contrast to white crystalline ins(4-bromo-2,3,5,6-tetramethyl phenyl)boron and 4,4'-diethynylbiphenyl precursors. Absorbance of BCMP is observed to be broad and featured two major UV/Vis absorption bands at 350 nm and 410 nm which can be ascribed to π-π* transition of the linker part and π-/½(Β) electron transition from linker to empty /^-orbital of boron respectively (Figure 13a). In contrast to blue emission from linker and non-emissive behaviour of ira(4-bromo- 2,3,5, 6-tetramethyl phenyl)boron, BCMP showed strong green emission with maxima at 520 nm (Figure 13b) and excitation spectra show two resolved bands at 350 nm and 410 nm. This large red shift in emission of BCMP clearly suggests interaction between extended linker (donor) and boron center (acceptor) through intramolecular charge transfer (ICT) interaction via conjugation. ICT process is validated by solvent dependent emission features of polymer; in a nonpolar solvent like hexane, BCMP shows local excited state (LE) emission with maxima at 410 nm originated from the extended linker, in contrast, in a highly polar solvent like water (H₂0) emission maxima is red shifted to 520 nm assigned to ICT (Figure 14). The dependence of emission maxima of the polymer with polarity of solvents demonstrates that there is indeed strong coupling between donor and acceptor in the excited state. This strong dependence of emission maxima with polarity of solvent indicates that excited state is stabilized by polar solvent due to high dipole moment. The intramolecular charge transfer behaviour of BCMP is further studied by using density functional theory (DFT), all the DFT calculations were performed on precursor and smallest unit (Figure 15) of the polymer using Gaussian 09 software (M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, Gaussian 09, Revision A.02; Gaussian, Inc.: Wallingford, CT, 2009) for all electronic and optical calculations, considering B3LYP functional (A. D. Becke, J. Chem. Phys. 1993, 98, 5648; C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785; and R. G. Parr, W. Wang, Density-Functional Theory of Atoms and Molecules, Oxford University Press, New York, 1989) and 6-31+G(d) basis set. Molecular orbital plots of the node and smallest unit of BCMP show that highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are mainly localized on the phenyl ring moieties and boron center respectively (Figure 15). Further, TD-DFT calculations suggest that the ground state and optically allowed excited state corresponds to HOMO and LUMO, respectively. This clearly suggests that, there is an occurrence of intramolecular charge transfer from the linker to the empty ρπ orbital of boron. Furthermore, electrostatic potential (ESP) maps of smallest unit of BCMP clearly reveal that the boron center is highly electron deficient (Figure 15b). Further, no changes in excitation spectra are observed by changing the solvent polarity suggest weak coupling interaction between donor and acceptor in the ground state (Figure 16). Theoretically predicted optical absorption of smallest unit (421.2 nm, f = 1.2151) using TD-DFT calculations compare fairly well with the experimental value (410 nm) and no changes in absorption maxima are observed with the change in polarity of solvents (Figure 16).

Fluoride Sensing and Capture

Based on the principle that boron with empty ρπ orbital in BCMP would accept e^" from anions and perturbs the intramolecular charge transfer process, which would induce change in fluorescent signal, we have studied the effect of F^" ion on ICT emission of BCMP. There are no visual colour changes observed in polymer on addition of F^" ion. Initial studies were done on BCMP (5 μΜ) dispersed in THF, the changes in the emission of BCMP upon incremental addition of F^" (TBAF, 13 mM) in THF were recorded. As shown in Figure 17 intensity of emission band at 520 nm corresponds to ICT decreases with addition of F^" ion and subsequently, concomitant appearance of blue emission band at 420 nm is observed and enhanced with increasing the amount of F^" ion. It is expected that, when F^" binds to boron, ICT gets blocked and results in decrease of ICT emission, however, alternatively linker gets excited resulting in π*-π emission localized on the extended linker; tetramethylphenyl fused 1,4-diethynylbiphenyl unit. To confirm that the blue emission is solely from the extended linker, we have calculated its excited state optical properties. It was found that the modified extended linker shows emission peak at 411 nm (1.9820 eV) (Figure 18), which is close to experimentally observed blue emission (420 nm). Also, the orbital diagrams (LUMO and HOMO) confirms that this extended linker shows the characteristic π*-π emission peak (SI to SO) (Figure 19), which further support hypothesis that the strong blue emission of F^" encapsulated CMP (F^"@ BCMP) is indeed originated from the extended linker and signifying its importance for turn-on sensing of F^" ion. It is worth mentioning, the emission colour of the solution remarkably changes from green to intense blue on F^" binding (Figure 20). Further, ESP plot suggests that on complexation of F^" , boron center loses electron deficient character whereas F^" turns to be the low electron density species (Figure 21). We have further calculated the optimized structure for the F^" bound smallest unit; as seen in Figure 22, F^" ion is indeed strongly bound to the boron center by donating electrons to boron. 'B-F' distance in F^"@ BCMP is observed to be 1.47 A which is close to B-F distance in BF₄ ^" (1.43 A) thereby suggesting strong interaction between 'B' and 'F' and the corresponding geometry shown in Figure 22.

Detection of F^" in water is a challenging issue; World health organization recommends F^" ion content in drinking water to be lower than 1.5 ppm. However, BCMP does not show significant change in emission spectra on incremental addition of fluoride ion in pure water due to high hydration enthalpy (Figure 23). Hence further experiments were carried out in organic-aqueous solvent mixture. Initial experiments were done with BCMP (5 / ) dispersed in DMSO/H₂0 having volume percentage ratio 8:2 mixture and titrated against tetrabutylammonium fluoride (TBAF) (15 mM, DMSO/H₂0, 8:2) with incremental addition of F^" ion. Figure 24a shows a gradual decrease of the emission intensity at 520 nm with simultaneous increase in the blue emission intensity at 410 nm with addition of F^". Blue emission is ascribed to π*-π emission of extended linker as discussed earlier. Nevertheless, the detection limit is observed to be about -20 ppm. While, the mixture of THF/H₂0 in 9: 1 volume percentage ratio is found to be promising for detection of lower concentration of F^" ion. As seen in Figure 24b, similar blockage of ICT emission and enhancement of blue emission from the linker is observed with incremental addition of F^" (3.5 mM) to BCMP dispersed in THF/H₂0. Strikingly, similar fluorescence response of BCMP is observed up to very low concentrations of F^". Figure 25, Stern- Volmer plot showing the florescence response of BCMP on addition of equivalents of fluoride ion (THF: H₂0, 9: 1, Intial concentration of F^" is 4.5x 10^"4 M), the corresponding intercept or the detection limit is found to be 2.6 . Interestingly, BCMP shows appreciable fluorescence response even with lower levels of F^" ion (final concentration, < 2.6 ) on soaking F^" with BCMP dispersion in THF/H₂O mixture for 15 min (Figure 26). This delay of fluorescence response for such low concentration of F^" may be attributed to the longer diffusion time of F^" ion to interact with boron present in the polymer. Binding constant for F^" ion to the BCMP is calculated from fluorescence titration data is found to be lx lO⁴ M^"1 (Figure 27). It is worth to note that BCMP is highly selective for F^" ion (Figure 28) and show no appreciable fluorescence response to other anions such as CI^", Br^", Γ, N0₃ -^", S0₄2- and C0₃2- . This high selectivity of BCMP to F^" ion may be due to sterically crowded binding environment created by substituent ortho methyl groups on phenyls around boron center. Most striking feature of F^" ion sensing with BCMP is its reversibility and recovery of sample. Owing to large hydration enthalpy of F^" ion, addition of excess water to F^"@BCMP, assynthesized polymer is regenerated with complete restoration of green emission and is recovered by simple centrifugation method (Figure 29).

In order to study the capability of BCMP in sequestration of F^", we have carried out ¹⁹F-NMR of TBAF solution soaked with BCMP (insoluble nature of BCMP restricted us to study the changes in ^UB-NMR). A solution of TBAF/dmso- (5 mM) is added to BCMP (O. lmg) and kept for 60 seconds and is centrifuged out. The clear decant solution thus obtained is studied by ¹⁹F-NMR for free F^" ion in solution (Figure 30). As expected, the signal intensity of free F^" in solution decreased drastically within 60 sec, and soaking for further 60 sec resulted in complete loss of 'F' signal in MR spectrum. This result clearly suggests that the F^" ion is indeed captured within the porous polymer and its coordination to boron center is evident from the blue emission of BCMP under UV light (Inset; Figure 30). Furthermore, 1H-NMR spectra of filtrate at different intervals did not show any peaks related to integral parts of the polymer which clearly suggest no disintegration of polymer on F^" ion binding (Figure 31&32). To further prove the polymer capture of F^", we have carried out elemental colour mapping of F^"@ BCMP powder isolated by the centrifugation of the dmso-i/⁵ dispersion. Strikingly, elemental mapping showed uniform distribution of 'F' throughout the polymer matrix which confirms that the F^" ion is indeed captured by BCMP through strong anion-boron interactions in the micropores of the polymer (Figure 33). These results clearly suggest that BCMP can not only recognize but also capture F^" ion. It is worth mentioning here that the selective recognition and capture or sequestration of F^" ion in a π- conjugated porous polymer is unprecedented and the detection limits are high in comparison to other discrete compounds and porous scaffolds (N. N. Adarsh, A. Grelard, E. J. Dufourc, P. Dastidar, Cryst. Growth Des. 2012, 12, 3369-3373; B. Chen, L. Wang, F. Zapata, G. Qian, E. B. Lobkovsky, J. Am. Chem. Soc. 2008, 130, 6718-6719). We have further tested the capability of BCMP to test F^" ion present in Colgate anticavity tooth paste by extracting it with THF/H₂O. As seen in Figure 34, with incremental addition of extract solution clear enhancement in the blue emission is observed.

In summary, the preceding results demonstrate rational design and synthesis of a Lewis acidic microporous organic polymer with high density of functional boron centers as recognition sites for selective detection of F^". The extended conjugation of linker through duryl groups facilitated turn-on fluorescent sensing of F^" ion by the obstruction of ICT phenomena. BCMP show high detection limit and strong boron-fluoride interactions allowed facile sequestration of F^" ion. We further believe that BCMP with strong ICT emission features would find applications in organic light-emitting diodes (OLEDs) and in sequestration of C0₂ via Lewis-acid-base interactions with boron.

Claims

We claim:

1. An electron deficient boron based conjugated microporous polymers (BCMP) comprising a polymeric network of triarylborane and an organic linkers wherein the triarylborane is attached with the organic linkers.

2. The electron deficient boron based conjugated microporous polymers (BCMP) as claimed in claim 1 comprising a boron appended triarylborane porous conjugated microporous polymers solid adsorbents, featuring triarylborane having Lewis acidic boron centers separated by organic linkers as integral part of polymeric network.

3. The electron deficient boron based conjugated microporous polymers as claimed in claim 1, wherein the triarylborane is selected from the group comprising of:

5. A process for the preparation of electron deficient boron based conjugated microporous polymers as claimed in claim 1, wherein said process comprising coupling reaction between a triarylborane moiety and the organic linker in presence of a solvent and a coupling catalyst.

6. The process as claimed in claim 5, wherein the solvent used is selected from a group comprising of dry DMF and Et₃N; THF and Toluene.

7. The process as claimed in claim 5, wherein the coupling catalyst used is selected from a group comprising of dry mixture Pd(PPh₃)₄ and Cul, Pd(PPh₃)₂Cl₂, Pd(dppe)Cl, Pd(dppe)Cl₂ and Pd(dppf)Cl₂. 8. The process as claimed in claim 5, wherein the triarylborane moiety is used in the range of 5 % to 20 % volume percentage.

9. The process as claimed in claim 5, wherein the organic linker is used in the range of 30 % to 50 % volume percentage.

10. The process as claimed in claim 5, wherein the triarylborane moiety and the organic linker are dissolved in the solvent at a temperature in the range of 25 to 30 °C.

11. The process as claimed in claim 5, wherein the coupling catalyst is added to the reaction mixture at a temperature in the range of 25 to 30 °C.

12. The process as claimed in claim 5, wherein the triarylborane moiety is a halogenated triarylborane. An electron deficient boron based conjugated microporous polymer (BCMP) having

14. The boron conjugated microporous polymers as claimed in claim 13 is three dimensional infinite porous polymer, and the value of 'n' is up to 64. 15. A process for the preparation of electron deficient boron based conjugated microporous polymers as claimed in claim 13, wherein said process comprising the steps of: a) dissolving tris(4-bromo-2,3,5,6-tetramethylphenyl)boron and 4,4'- diethynylbiphenyl is in a solvent to obtain a reaction mixture; and

16. The process as claimed in claim 15, wherein the solvent used in step (a) is selected from a group comprising of dry DMF and Et₃N; THF and Toluene. 17. The process as claimed in claim 15, wherein the coupling catalyst used in step (b) is selected from a group comprising of dry mixture Pd(PPh₃)₄ and Cul, Pd(PPh₃)₂Cl₂, Pd(dppe)Cl, Pd(dppe)Cl₂ and Pd(dppf)Cl₂. 18 The process as claimed in claim 15, wherein the tris(4-bromo-2,3,5,6- tetramethylphenyl)boron is used in the range of 5 % to 20 % volume percentage. 19. The process as claimed in claim 15, wherein the 4,4'-diethynylbiphenyl is used in the range of 30 % to 50 % volume percentage.

20. The process as claimed in claim 15, wherein the tris(4-bromo-2,3,5,6- tetramethylphenyl)boron and 4,4'-diethynylbiphenyl is dissolved in the solvent at a temperature in the range of 25 to 30 °C.

21. The process as claimed in claim 15, wherein the coupling catalyst is added to the reaction mixture at a temperature in the range of 25 to 30 °C. 22. A process for detection of fluoride in a substance which contains fluoride comprising:

23. The process for detection as claimed in claim 22, wherein the organic-aqueous solvent mixture is selected from the group comprising DMSO and H₂0, THF and H₂0, and DMF and H₂0.

24. The process for detection as claimed in claim 22, wherein the volume percentage ratio of organic-aqueous solvent is in the range of 7-10 : 0.5-3. 25. The process for detection as claimed in claim 22, wherein the volume percentage ratio of DMSO/H₂0 is 8:2.

26. The process for detection as claimed in claim 22, wherein the volume percentage ratio of THF/H₂0 is 9: 1. The process for detection as claimed in claim 22, wherein the BCMP shows selective blue emission for F^" ion in aqueous mixtures with a detectable limit of 2.6 .