WO2016050204A1

WO2016050204A1 - Aggregation-induced emission and aggregation-promoted photochromism of bis(diarylmethylene) -dihydroacenes

Info

Publication number: WO2016050204A1
Application number: PCT/CN2015/091121
Authority: WO
Inventors: Benzhong Tang; Zikai HE; Wing Yip Lam
Original assignee: Benzhong Tang
Priority date: 2014-09-30
Filing date: 2015-09-29
Publication date: 2016-04-07

Abstract

Provided is a series of novel polycyclic molecules bis(diarylmethylene) -dihydroacenes with aggregation-induced emission characteristics and their applications for organic photochromic materials.

Description

Aggregation-Induced Emission and Aggregation-Promoted Photochromism of Bis (diarylmethylene) -dihydroacenes

The present application claims the benefit of priority of U.S. Provisional Application No. 62/071,688, which was filed on Sep. 30, 2014. The entire text of the aforementioned application is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a series of novel polycyclic molecules bis (diarylmethylene) -dihydroacenes with aggregation-induced emission characteristics and their applications for organic photochromic materials.

BACKGROUND OF THE INVENTION

Aggregation-induced emission (AIE) refers to a phenomenon that a class of luminogens is molecularly nonemissive but become highly emissive when cluster into aggregates. Luminogenic materials with AIE characteristics have attracted extensive interest and found varied applications. Through mechanistic decipherment of photo-physical process, structure-property relationships were derived and structural design strategies for generating new AIE luminogens (AIEgen) were developed. Based on two archetypal AIEgens tetraphenylethene (TPE) and hexaphenylsilole (HPS) which contain muitiple phenyl peripheries (rotor) linked to the ethylene and silole core (stator) via single bonds (axis) , the restriction of intramolecular rotation (RIR) process was proposed as the main cause of the AIE effect. This RIR mechanism has been successfully utilized to explore a large variety of new fluorescent and phosphorescent AIEgens. However, some newly emerging AIE systems, which are absent from multiple rotors, brought about some ambiguous issues to the RIR mechanism. The rapid development of the AIE area is calling for a more comprehensive mechanism. As well known, rotation and vibration are the two main modes of molecular motions accompanied by energy consumption. We proposed that the AIE effect maybe mainly originate from the restriction of intramolecular rotations (RIR) and vibrations (RIV) . Upon aggregation, the substantial intramolecular rotations and vibrations are restricted to block non-radiative decay pathway and open the radiative decay pathway. Therefore, we integrated the RIR with RIV as the restriction of intramolecular motions (RIM) , which will be of great importance for the extending the AIE scope.

Photochromic materials have been attracting increasing interest for their great importance in fundamental research and practical applications. A large number of photo-chromic systems, including azobenzene spiropyran, diaryl-ethene etc, have been reported and exhibited good performances in photochemical, biological and nanotechnological applications. Exploring novel photochromic systems and understanding their working mechanism is drawing continuous attention. Particularly, the development of facilely synthesized novel photochromic system is highly challenging and demanded.

On the basis of the RIM principle, a novel series of polycyclic molecules bis (diarylmethylene) -dihydroacenes were designed and synthesized, which were found AIE active and novel AIE promoted photochromism properties with facile synthesis and good thermal stability as well as fast photo-response.

SUMMARY OF THE INVENTION

It is therefore an object of the present object to provide a series of novel polycyclic molecules bis (diarylmethylene) -dihydroacenes with aggregation-induced emission characteristics and their applications for organic photochromic materials.

The new AIE compounds are selected from the following formula (I) to (III) :

wherein each Ar is independently selected from:

Wherein R is independently selected from H, halo, hydroxyl, alkyl, alkoxy, alkenyl, alkynyl, acetyl, aryl, heteroaryl, cycloalkyl, heterocycloalkyl, or heteroalkyl that is optionally substituted.

In some preferred embodiment, Ar is independently selected from:

In some more preferred embodiment, Ar is independently selected from:

In some preferred embodiment, R is independently selected from H, halo, C_1-6 alkyl, C_1-6 alkoxy, C_1-6 alkylthio, NO₂, CN, OH, NH₂, C_1-6 monoalkylamino, C_1-6 dialkylamino.

In some more preferred embodiment, R is independently selected from H, C_1-4 alkyl, C_1-4 alkoxy, C_1-4 alkylthio, NO₂, CN, OH, NH₂, C_1-4 monoalkylamino, C_1-4 dialkylamino.

In the present invention, the AIE compounds are selected from the following formula (I’ ) to (III’ )

Wherein, Ar is defined as above.

In the present invention, at least one hydrogen atom linked to a double bond is needed to undergo [2+2+2] electrocyclic photocyclization reaction.

In the present invention, the AIE compounds are selected from the following formula (I” ) to (III” )

The present herein provides a novel aggregation-promoted photochromic system based on a polycyclic hydrocarbon compound. This system is facilely synthesized and exhibits good thermal stability as well as a fast photo-response.

In the present invention, the following compounds are the most preferal:

The present invention also provides a method for preparing the compound (I) - (III) , which comprises the following steps:

(1) Corey-Fuchs reaction: using triphenylphosphine and carbon tetrabromide to afford tetrabromo precursors,

(2) typical Suzuki-Miyaura reaction: using K₂CO₃ and Pd (PPh₃) ₄ led to the final products, optionally, purifying by recrystallization from chloroform-hexane without column chromatography.

Specially, the method comprises:

(1) a mixture of CBr₄ and PPh₃ in dry solvent (such as toluene) was stirred at room temperature before formula (I-1) , (II-1) or (III-1) was added in one portion and the solution was heated to reflux, then formula (I-2) , (II-2) or (III-2) was obtained.

More preferred, the step (1) also contains the following step: the reaction mixture in step

(1) was cooled to room temperature； the solid was removed by filtration and washed with solvent (such as toluene) .

Further more preferred, the step (1) also contains: the filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was triturated with solvent (such as ethanol) and filtered to give pure product.

(2) To a solution of formula (I-2) , (II-2) or (III-2) and aryl boronic acid in solvent (such as toluene) was added the mixed solvent (such as ethanol and water) . The mixture was stirred at room temperature and bubbled with nitrogen. Then K₂CO₃ and Pd (PPh₃) ₄ were added and the mixture was heated to reflux, then the product of formula (I) , (II) , (III) .

More preferred, the step (2) also contains the following step: the reaction mixture was cooled to room temperature and filtered through a pad, washing with organic solvent (such as dichloromethane) until the filtrate was clean.

Further more preferred, the step (2) also contains: the filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was then triturated with ethanol and filtered to give product.

The presented invention comprises the following steps:

Wherein, Ar is defined as above.

The present invention also is directed to a method of applications of bis

(diarylmethylene) -dihydroacenes for organic photochromic materials.

The present invention also is directed to a method of applications of bis

(diarylmethylene) -dihydroacenes with organic photochromic properties in light-emitting diodes, optical amplifiers, optical information storage, liquid crystal displays and bio-sensing, logic gates, non-destructive readout, and biological probes.

The terms explanation

The terms “alkyl” used alone or as part of a larger moiety as “alkoxy” , means a straight-chain (i.e., unbranched) or branched, substituted or unsubstituted alphatic hydrocarbon. Unless otherwise specified, alkyl or contains 1-20 carbon atoms. In some embodiments, alkyl contains 1-10 carbon atoms. In still other embodiments, alkyl contains 1-8 carbon atoms.

Examples which may be mentioned are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl, isohexyl, heptyl, iso-heptyl, octyl and isooctyl group.

The terms “alkoxy” on the basis of the above generally represents a straight-chain or branched-chain alkyl bonded through an oxygen atom. Alkoxy having 1 to 20 carbon atoms are particularly preferred. Examples which may be mentioned are methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, pentoxy, hexyloxy, heptyloxy or octyloxy group. The terms “alkenyl” according to the above generally means a straight-chain or branched, containing 2 to 20 carbon atoms, and having one or more double bonds, preferably one or two double bond. In some embodiments, alkenyl contains 2-10 carbon atoms and one double bond. In other particularly preferred embodiments, alkenyl contains 2-8 carbon atoms and one double bond. Examples can be mentioned are allyl, propenyl, isopropenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, isohexenyl, heptenyl, isoheptenyl, octenyl and isooctenyl group.

The terms “alkynyl” according to the above general represents a straight chain or branched chain, containing 2 to 12 carbon atoms and one or more and preferably one or two triple bond hydrocarbon group. Containing 2 to about 10 carbon atoms and one triple bond hydrocarbon is preferred. Containing 2-8 carbon atoms and one triple bond hydrocarbon it is particularly preferred. Examples which may be mentioned are ethynyl, 2-butynyl, 2-pentynyl and 2-hexynyl.

The terms “acyl” according to the above general represents a straight chain or branched chain, containing 1 to 20 carbon atoms and one or more and preferably one or two carbonyl.

The terms “cycloalkyl” represents a monocyclic cycloalkyl group having generally 3 to 7, preferably 5 or 6, carbon atoms； cycloalkyl groups which may be mentioned by way of example are cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl.

The terms “heterocyclyl” represents a monocyclic heterocyclic radical having 5 or 6 ring atoms and up to 3, preferably up to 2, heteroatoms and/or hetero groups from the group consisting of N, O, S. Preference is given to 5-or 6-membered monocyclic saturated heterocyclyl radicals having up to two heteroatoms from the group consisting of O, N and S, by way of example and by way of preference pyrrolidin-2-yl, pyrrolidin-3-yl, pyrrolinyl, tetrahydrofuranyl, tetrahydrothienyl, pyranyl, piperidin-1-yl, piperidin-2-yl, piperidin-3-yl, piperidin-4-yl, 1, 2, 5, 6-tetrahydropyridin-3-yl, 1, 2, 5, 6-tetrahydropyridin-4-yl, thiopyranyl, morpholin-1-yl, morpholin-2-yl, morpholin-3-yl, piperazin-1-yl, piperazin-2-yl.

The terms “aryl” used alone or as part of a larger moiety as “aralkyl” , “aralkoxy” , “aryloxyalkyl” , represents an aromatic cyclic radical (such as monocyclic, bicyclic, and tricyclic ring system) having generally 6-20 ring atoms. An aromatic monocyclic radical containing 6-14 ring atoms (more preferred, 6 ring atoms) is preferred. Examples are phenyl.

The terms “heteroaryl” used alone or as part of a larger moiety as “heteroaralkyl” , “heteroaralkoxy” , “heteroaryloxyalkyl” represents an aromatic cyclic radical (such as monocyclic, bicyclic, and tricyclic ring system) having generally 5-20 ring atoms and up to 4 heteroatoms from the group consisting of S, O and N.

An aromatic monocyclic radical containing 5-14 ring atoms (more preferred, 5 or 6 ring atoms) is preferred. Examples are thienyl, furyl, pyrrolyl, thiazolyl, oxazolyl, isoxazolyl, oxadiazolyl, pyrazolyl, imidazolyl, pyridyl, pyrimidyl, pyridazinyl, pyrazinyl.

The terms “heteroatoms” means one or more of O, S, N.

Halo represents F, Cl, or Br in the present invention.

The term “optionally substituted” refers to the replacement of hydrogen radicals in a given structure with the radical of a specified substituent. Unless otherwise indicated, an optionally substituted group may have a substituent at each substitutable position of the group, and when more than one position in any given structure may be substituted. Suitable substituents are generally selected from halogen, C1-6 alkyl, C1-6 alkoxy, C1-6 alkylthio, NO2, CN, OH, NH2, C1-6 monoalkylamino, C1-6 dialkylamino. Examples are methylamino, ethylamino, n-propylamino, isopropylamino, tert-butylamino, N, N-dimethylamino, N, N-diethylamino, N-ethyl-N-methylamino, N-methyl-N-n-propylamino, N-isopropyl-N-n-propylamino and N-tert-butyl-N-methylamino.

The development of facilely synthesized novel photochromic systems is highly

challenging and in demand. Reported herein is a novel aggregation-promoted

photochromic system based on a pure polycyclic hydrocarbon compound. This system is facilely synthesized and exhibits good thermal stability as well as a fast photo-response.

BRIEF DESCRIPTION OF FIGURES AND TABLES

Figure 1. (Left) PL spectra of BDPM-DHA in THF/water mixtures with different water fractions (f_w) . (Right) Plot of PL peak intensity vs water fraction (f_w) of the aqueous mixture. (Concentration: 10 μM； excitation wavelength: 320 nm. )

Figure 2. (Left) PL spectra of BDPM-DHP in THF/water mixtures with different water fractions (f_w) . (Right) Plot of PL peak intensity vs water fraction (f_w) of the aqueous mixture. (Concentration: 10 μM； excitation wavelength: 340 nm. )

Figure 3. Crystal structure of BDPM-DHT·CHCl3. (A) Top view and (B) - (C) side view of BDPM-DHT with carbon atom positions shown as 50％probability ellipsoids； (D) molecular packing of BDPM-DHT as viewed along the a axis of the unit cell with diphenylmethylene group shown in pink. (Carbon, chlorine and hydrogen atoms are shown in gray, green, and white, respectively. )

Figure 4. Crystal structure of BDPM-DHA. (A) Top view and (B) - (C) side view of BDPM-DHA with carbon atom positions shown as 50％probability ellipsoids； (D) molecular packing of BDPM-DHA as viewed along the a axis of the unit cell. (Carbon and hydrogen atoms are shown in gray and white, respectively. )

Figure 5. Crystal structure of BDPM-DHP. (A) Top view and (B) - (C) side view of BDPM-DHP with carbon atom positions shown as 50％probability ellipsoids； (D) molecular packing of BDPM-DHP as viewed along the b axis of the unit cell. (Carbon and hydrogen atoms are shown in gray and white, respectively. )

Figure 6. (A) Up: room light digital images of BDPM-DHT crystals before (left) and after (right) UV irradiation； Down: UV light digital images of BDPM-DHT crystals before (left) and after (right) UV irradiation. (B) Changes in the UV-vis reflectance spectra of BDPM-DHT crystal upon irradiation at λ＝365 nm. (C) The plot of the reflectance change at λ＝498 nm as a function of UV irradiation and visible light exposure time. (D) Fatigue resistance of crystal BDPM-DHT upon irradiation with 365 nm (1 minute) and standing in room light (1 minute) alternatively. (The reflectance was measured at 498 nm. )

Figure 7. TGA and DSC thermogram of BDPM-DHT at a heating rate of 10℃/min. (One CHCl₃ molecule per BDPM-DHT molecule was trapped in the crystal lattice and can be removed at ～80 degree with crystal collapse)

Figure 8. UV-vis absorption spectra of BDPM-DHT in THF (left) and chloroform (right) solutions before (dark line) and after (red line) UV lamp shining for 5 minutes.

Figure 9. Changes in the UV-vis reflectance spectra of BDPM-DHT crystal upon room light treatment (Initial: UV irradiation at λ＝365 nm for 3 minutes) .

Figure 10. Proposed mechanism of the photochromic process and calculated reaction coordinate diagram.

Figure 11. Calculated energy differences of BDPM-DHA system (left) and BDPM-DHP system (right) .

Figure 12. Molecular orbital amplitude plots (isovalue＝0.03) of HOMO and LUMO energy levels of BDPM-DHT (A, open form) and DPBNP-H (B, closed form) .

Figure13. Calculated molecular structure (left) and molecular orbital amplitude plots (isovalue＝0.02) of HOMO (middle) and LUMO (right) energy levels of DPBNP.

Figure 14. High resolution mass spectrum of BDPM-DHT crystals exposed to UV light for two days in air.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description of the invention is provided to aid those skilled in the art in practicing the present invention. However, the following detailed description of the invention should not be constructed to unduly limit the present invention. Variations and modifications in the embodiments discussed may be made by these of ordinary skill in the art without departing from the scope of the present inventive discovery.

This invention provides a series of novel polycyclic molecules bis (diarylmethylene) -dihydroacenes with aggregation-induced emission characteristics and their applications for organic photochromic materials

In the invention, four molecules with the chemical structures illustrated as following were synthesized as typical examples.

The synthetic routes were demonstrated as following and the synthetic details were described in EXAMPLES for further reference.

From commercial available acenequiones, BDPM-DHA, BDPM-DHT, BDTM-DHT and BDPM-DHP were synthesized according to the literature method with modifications.

After Corey-Fuchs reaction using triphenylphosphine and carbon tetrabromide to afford tetrabromo precursors, the typical Suzuki-Miyaura reaction led to the final products in high yield, which were purified by recrystallization from chloroform-hexane without column chromatography.

The photophysical properties of BDPM-DHA and BDPM-DHP were investigated both in their solutions and aggregate states. It was verified that the compounds behave as typical AIE compounds, no-emission in their dilute THF solutions and a fluorescence emission at 455 nm and 530 nm, respectively, at their aggregate states (see Figure 1 and Figure 2) . The AIE properties of BDPM-DHA and BDPM-DHP should originate from the effective RIM process and the turn-on radiative pathway.

Single crystals of BDPM-DHA, BDPM-DHT and BDPM-DHP qualified for X-ray crystallography were grown by slowly diffusing n-hexane to CHCl₃ solutions. Shown in Figure 3 is the crystal structure of BDPM-DHT, which reveals that the backbone of BDPM-DHT adopts a highly contorted structure. As highlighted in Figure 3A, the C-C bonds shown in red, green and blue have bond lengths close to typical C-C double bond； typical C-C single bond and benzene C-C bond, respectively. These bond lengths indicate that the diphenylmethyl groups have very weak conjugation with the tetracene backbone in agreement with its contorted structure.

Viewed from the side, BDPM-DHT molecule bends by large dihedral angles for both tetracene backbone (Figure 3B) and diphenylmethylene groups (Figure 3C) . This nonplanar structure can be attributed to the stereo repulsion among them. Additionally, solvent molecules CHCl₃ are trapped in the crystal lattice by very strong CH-to-π interaction shown in dash red line. Shown in Figure 3D is the molecular packing of BDPM-DHT, which is built up with CHCl₃ molecules as linkages through CH…π (red arrow) , CH…C (dark arrow) , CH…Cl (blue arrow) , Cl…C (violet arrow) interactions. As a result, the BDPM-DHT molecules are locked and separated in the crystal. In other words, the BDPM-DHT becomes emissive because nonradiative decay pathways such as intramolecular rotation, intramolecular vibration and π-π interaction were blocked in the crystals according to the RIM mechanism. Crystal structures of BDPM-DHA and BDPM- DHP adopt similar distorted structures as summarized in the Supporting Information (see Figure 4-5) .

As shown in Figure 6A, colorless needle shaped crystals of BDPM-DHT exhibit blue emission under UV lamp irradiation (365nm) in accordance with its AIE characteristic. It was unexpectedly found that the colorless crystals became red when the UV lamp was removed. Even in a very short irradiation time (～1 second) , obvious color change can be observed. Meanwhile, the blue emission significantly faded. When placed under room light for several minutes, the red crystals were gradually returned to colorless accompanied with blue emission recovery. Integrating the absorption and emission behaviors, BDPM-DHT crystals exhibit novel photochromic effects.

To further investigate the red crystals color change, they are treated under different conditions. When placed in darkness at room temperature for 2 days, the red crystals remained unchanged, indicating that they are thermally irreversible which is indispensable to the application as optical memories and switches for a photochromic system. Even placed at elevated temperature about 60℃ before the crystal collapse (see Figure 7) , the red crystals can survive for several hours in darkness. X-ray crystallographic analysis on the red crystals of BDPM-DHT was also performed under dark but the results revealed that the red crystals are identical to the colorless ones, suggesting the photochromism occurred in a very small amount which is not detectable by X-ray crystallography. After cracking the red crystals, the colorless inner part told us that the photochromism occurred only on the crystal surface. Further prelonging the UV irradiation time to 10 minutes, the inner part keeps unreacted, which may be attributed to the UV absorption of red crystal surface.

The UV response of BDPM-DHT in solution state was also tested in 10-5 M THF and CHCl₃ solutions monitored by UV-vis absorption. However, no detectable change was observed upon UV irradiation for 5～10 minutes (see Figure 8) . Just like the AIE, the aggregation may play an important role in the crystal-state photochromic process. In the solution, the UV excited molecules can easily non-radiatively decay through intramolecular motions and solvent molecule collision. Upon aggregation, these pathways were restricted and the blue emission followed by photochromic reaction was facilitated. As a result, it is an aggregation promoted-photochromism system.

Photochromic processes of BDPM-DHT crystals were then investigated by UV-vis reflectance absorption spectroscopy. Before UV irradiation, the colorless crystal exhibits a maximum absorption at 370 nm, which suggests the weak conjugation in the molecules. However, upon irradiation at 365 nm, a strong absorption band peaked at 498 nm emerges and increases with the progress of photo-irradiation (Figure 6B) . The absorbance reaches half-peak width within 5 seconds and saturates after 60 seconds. In addition, the progress of room light response was also recorded using the same method (see Figure 9) . The increase and the decrease of the reflectance at 498 nm as a function of time were plotted and used to monitor the photo response processes. As shown in Figure 6C, the crystals responded rapidly in the first 10 seconds and almost finished in 60 seconds towards UV and visible light. As shown in Figure 6D, BDPM-DHT crystals were repeatedly switched between the red and colorless state for 10 times, and the reflectance at 498 nm stayed almost constant without any apparent degradation, indicating their excellent fatigue resistance.

For the presence of two fixed cis-stilbene motifs and short distance between the phenyl ring and the tetracene backbone (Figure 3A) , mechanism for the color change of BDPM-DHT crystal upon UV irradiation was proposed as depicted in Figure 10. It is well known that cis-stilbene can undergo a photocyclization reaction to yield dihydrophenanthrene. Therefore, the color change is ascribed to photo-induced ring closing from BDPM-DHT to DPBNP-H, which has a larger π electron delocalization throughout the molecule as highlighted in bold-red line. On the other hand, DPBNP-H has a smaller HOMO-LUMO gap as well as the red shift UV-vis absorption. Due to small amount and the fast response towards room light, attempts to isolation DPBNP-H were tried but failed. Therefore, DFT calculations and photo oxidation conversion were applied to verify the hypothesis and investigate the intermediate DPBNP-H.

The dihydro-phenanthrene is highly unstable and returns to stilbene very quickly even in the darkness. Therefore, phenyl rings of stilbene are usually replaced by hetero aryl rings such as thiophene, furan and pyrrole to prolong the lifetimes of the dihydro intermediate, because hetero aryl rings have smaller aromaticity. As mentioned above, DPBNP-H is thermally irreversible, which is quite difficult to be realized for stilbene. From BDPM-DHT to DPBNP-H, three benzene rings are broken. However, after DFT calculation, we found the energy difference between BDPM-DHT and DPBNP-H is merely about 149 kJ/mol, which is close to the resonance energy of only one benzene ring. The newly formed π-conjugation was thought to make a big contribution to stabilize the intermediate DPBNP-H. Meanwhile, the same calculations were performed on BDPM-DHA and BDPM-DHP systems. The energy difference increases to 158 kJ/mol for BDPM-DHA and 164 kJ/mol for BDPM-DHP, respectively, which are present by their no photochromic behavior under the same condition. Among the three systems, BDPM-DHT has the highest similarity between backbone of BDPM-DHT and that of DPBNP-H. For BDPM-DHT, the aromatic parts of tetracene backbone keep almost no change before and after the cyclization, regarding as one naphthalene ring and one benzene ring. However, for BDPM-DHA, the aromatic parts of anthracene backbone change from two benzene rings to one naphthalene ring. For BDPM-DHP, the aromatic parts of pentacene backbone change from two naphthalene rings to one anthracene ring and one benzene ring. According to the Clar’s rule, such changes are disfavored in energy. (see Figure 11) As shown in Figure 12, the HOMO and LUMO energy levels of BDPM-DHT are calculated and found localized at dimethylene-cyclohexadiene part and the naphthalene part, respectively, proving its weak intramolecular conjugation and distorted structures. For DPBNP-H, both HOMO and LUMO are delocalized throughout the newly formed π-electrons. Meanwhile, the energy gap between the HOMO and LUMO is dramatically decreased from 4.09 eV to 2.40 eV, which are in good agreement with its optical energy gap and the color change from colorless to red.

In the presence of air, the dihydrophenanthrene can be oxidized to phenanthrene irreversibly. To further verify our mechanism, we tried to get oxidated product DPBNP from the photocyclization intermediate DPBNP-H. On one hand, we extended the UV irradiation time to 2 days in air. The BDPM-DHT crystal surface irreversibly turned yellow and a peak related to the DPBNP appeared in high resolution mass spectrum (Figure 14) . On the other hand, we used Katz-modified Mallory photocyclization method to treat BDPM-DHT and DPBNP was obtained in a high yield. To our surprise, the reaction was completed in 20 minutes, which was much faster than that of BDPM-DHA and BDPM-DHP. The photochromism of BDPM-DHT should help the formation of dihydro intermediate and accelerate the reaction. It was worth noting that the DPBNP is an an ACQ molecule, which is opposite to its precursor BDPM-DHT (AIE) . The partial lock of phenyl rings and large π-plane formation should account for its ACQ property.

In summary, this study puts forth a new photochromic system based on an AIE luminogen, which is conducted by polycyclic hydrocarbon compound. From commercially available starting materials, grams compounds were successfully synthesized through simple reactions in high yield. Particularly, fast responsive, photo-reversible and thermo-irreversible photochromic properties were realized in the solid state, which are crucial for practical application. Photocyclization reaction was proposed as the mechanism for the photochromic process, whose energy barrier is partially counterbalanced by newly formed π-conjugation and the tetracene backbone. Similar to AIE, the only solid state photochromic response makes BDPM-DHT the first aggregation-promoted photochromic system, which is facilitated by RIM and functions as a novel photochromic system.

EXAMPLES

Having described the invention, the following examples are given to illustrate specific applications of the invention including the best mode now known to perform the invention. These specific examples are not intended to limit the scope of the invention described in this application.

Example 1

Step (1) : Preparation of 5, 12-bis (dibromomethylene) -5, 12-dihydrotetracene A mixture of CBr₄ (8.6 g, 25.9 mmol) and PPh₃ (13.6 g, 51.8 mmol) in 100 ml dry toluene was stirred for 30 minutes at room temperature before 5, 12-tetracenequinone (2.06 g, 8.0 mmol) was added in one portion and the solution was heated to reflux for 24 h. The reaction mixture was cooled to room temperature； the solid was removed by filtration and washed with toluene. The filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was triturated with ethanol and filtered to give pure product (4.3 g) in 95％yield.

1H-NMR (CDCl₃) δ (ppm) : 8.26 (s, 2H) , 7.86 (m, 4H) , 7.3 (dd, J₁＝6.4 Hz, J₂＝3.2 Hz, 2H) , 7.31 (dd, J₁＝5.6 Hz, J₂＝3.2 Hz, 2H) . ¹³C-NMR (CDCl₃) δ (ppm) : 90.59, 127.25, 127.33, 127.44, 127.93, 128.29, 131.79, 133.36, 136.17, 139.73. MALDI-TOF mass: m/z＝569.7479 (cacld. 569.7475) .

Step (2) Preparation of 5, 12-bis (diphenylmethylene) -5, 12-dihydrotetracene (BDPM-DHT)

To a solution of 5, 12-bis (dibromomethylene) -5, 12-dihydrotetracene (2.26 g, 4.0 mmol) and phenyl boronic acid (3.90 g, 32 mmol) in 100 mL toluene was added 5 ml ethanol and 5 ml water. The mixture was stirred at room temperature and bubbled with nitrogen for 30 minutes. Then K₂CO₃ (5.52 g, 40 mmol) and Pd (PPh₃) ₄ (0.23 g, 0.20 mmol) were added in one portion and the mixture was heated to reflux for 24 hours. The reaction mixture was cooled to room temperature and filtered through a pad (silicon gel height: 5 cm), washing with dichloromethane until the filtrate was clean. The filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was then triturated with ethanol and filtered to give product (2.18 g) in 97％yield. After dissolving in CHCl₃ and putting them in the hexane atmosphere, high purity product was obtained as colorless crystals after 2 days.

1H-NMR (CDCl₃) δ (ppm) : 7.47 (m, 10H) , 7.35 (dd, J₁＝6.4 Hz, J₂＝3.2 Hz, 2H) , 7.31-7.13 (m, 14H) , 7.03 (dd, J₁＝6.0 Hz, J₂＝3.6 Hz, 2H) , 6.75 (dd, J₁＝6.0 Hz, J₂＝3.2 Hz, 4H) . ¹³C-NMR (CDCl₃) δ (ppm) : 125.52, 126.71, 126.76, 126.98, 127.63, 128.13, 128.26, 128.38, 129.69, 129.78, 131.28, 135.64, 135.74, 138.02, 140.41, 142.44, 142.46. MALDI-TOF mass: m/z＝558.2359 (cacld. 558.2348) .

Example 2

To a solution of 5, 12-bis (dibromomethylene) -5, 12-dihydrotetracene (2.26 g, 4.0 mmol) and 2-thionyl boronic acid (4.10 g, 32 mmol) in 100 mL toluene was added 5 ml ethanol and 5 ml water. The mixture was stirred at room temperature and bubbled with nitrogen for 30 minutes. Then K₂CO₃ (5.52 g, 40 mmol) and Pd (PPh₃) ₄ (0.23 g, 0.20 mmol) were added in one portion and the mixture was heated to reflux for 24 hours. The reaction mixture was cooled to room temperature and filtered through a pad (silicon gel height: 5 cm), washing with dichloromethane until the filtrate was clean. The filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was then triturated with ethanol and filtered to give product (1.86 g) in 80％yield. After dissolving in CHCl₃ and putting them in the hexane atmosphere, high purity product was obtained as colorless crystals after 2 days.

Example 3

Scheme S1 Synthesis of 9, 10-bis (diarylmethylene) -9, 10-dihydroanthracne (R-DHA) .

Reagents and conditions: (i) CBr₄, PPh₃, toluene, 80℃； (ii) aryl boronic acid, [PPh₃] ₄Pd, K₂CO₃, toluene, 110℃.

Step (1) : Synthesis of 9, 10-bis (dibromomethylene) -9, 10-dihydroanthracne:

A mixture of CBr₄ (14.940 g, 45.00 mmol) and PPh₃ (20.960 g, 80 mmol) in 100 ml of dry toluene was stirred for 20 minutes at room temperature before anthracene-9, 10-dione (2.080 g, 10 mmol) was added in one portion and the solution was heated to 80℃ for 24 h.The reaction mixture was cooled to room temperature； the solid was removed by filtration and washed with toluene. The filtrates were rotavaped and the crude product was obtained. The crude product was triturated with ethanol to give pure product (4.120 g) in 78％yield. ¹H-NMR (CDCl₃) , δ (ppm) : 7.83 (m, J＝3.2 Hz, 4H) , 7.28 (m, J＝3.2 Hz, 4H)； ¹³C-NMR (CDCl₃) δ (ppm) : 139.59, 135.95, 127.75, 127.13, 90.49.

Step (2) : Synthesis of 9, 10-bis (diphenylmethylene) -9, 10-dihydroanthracene (R-DHA) To a solution of 9, 10-bis (dibromomethylene) -9, 10-dihydroanthracene (1.59 g, 4.0 mmol) and aryl boronic acid (30 mmol) in 100 mL toluene was added 5 ml ethanol and 5 ml water. The mixture was stirred at room temperature and bubbled with nitrogen for 30 minutes. Then K₂CO₃ (5.52 g, 40 mmol) and Pd (PPh₃) ₄ (0.23 g, 0.20 mmol) were added in one portion and the mixture was heated to reflux for 24 hours. The reaction mixture was cooled to room temperature and filtered through a pad (silicon gel height: 5 cm) , washing with dichloromethane until the filtrate was clean. The filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was then triturated with ethanol and filtered to give product (1.65 g) in 85％yield. After dissolving in CHCl₃ and putting them in the hexane atmosphere, high purity product was obtained as colorless crystals after 2 days. Step (2) : Synthesis of 9, 10-bis (diarylmethylene) -9, 10-dihydroanthracne

9, 10-bis (diphenylmethylene) -9, 10-dihydroanthracne (BDPM-DHA) :

The compound was obtained as white solid (2.060 g) in 81％yield. ¹H-NMR (CDCl₃) , δ (ppm) : 7.41 (d, J＝7.2 Hz, 8H) , 7.27 (q, J＝7.2 Hz, 8H) , 7.19 (t, J＝3.2 Hz, 4H) , 6.98 (t, J＝3.2 Hz, 4H) , 6.71 (t, J＝3.2 Hz, 4H) ； ¹³C-NMR (CDCl₃) , δ (ppm) : 142.64, 139.98, 137.89, 135.72, 129.82, 128.35, 128.06, 126.79, 125.28. [M + H] ⁺: 509.2225； found, 509.2236.

9, 10-bis (di-4’ -methoxylphenylmethylene) -9, 10-dihydroanthracene (ADHA) :

The compound was obtained as white solid (2.360 g) in a yield of 75％. ¹H-NMR (CDCl₃) , δ (ppm) : 7.26 (d, J＝8.0 Hz, 8H) , 7.01 (m, J＝8.0 Hz, 4H) , 6.80 (d, J＝2.8 Hz, 8H), 6.74 (d, J＝8.0 Hz, 4H) , 3.77 (s, 12H) ； ¹³C-NMR (CDCl₃) , δ (ppm) : 158.28, 138.90, 138.25, 135.34, 135.30, 130.94, 128.01, 125.11, 113.58, 55.26. [M + H] ⁺: 565.2851； found, 565.2837.

9, 10-bis (di-p-tolylmethylene) -9, 10-dihydroanthracne (TDHA) :

The compound was obtained as white solid (2.490 g) in a yield of 88％. ¹H-NMR (CDCl₃) , δ (ppm) : 7.26 (d, J＝8.0 Hz, 8H) , 7.07 (d, J＝7.6 Hz, 8H) , 7.00 (q, J＝3.2 Hz, 4H) , 6.72 (t, J＝5.6 Hz, 4H) , 2.29 (s, 12H) ； ¹³C-NMR (CDCl₃) , δ (ppm) : 139.95, 139.82, 138.17, 136.18, 135.39, 129.66, 129.01, 128.02, 125.10, 21.28. [M + H] ⁺: 629.2647； found, 629.2741.

Example 4

Scheme S2 Synthesis of 6, 13-bis (diphenylmethylene) -6, 13-dihydropentacene (R-DHP) . Reagents and conditions: (i) CBr₄, PPh₃, toluene, 80℃； (ii) aryl boronic acid, [PPh₃] ₄Pd, K₂CO₃, toluene, 110℃.

Step (1) : Preparation of 6, 13-bis (dibromomethylene) -6, 13-dihydropentacene A mixture of CBr₄ (8.6 g, 25.9 mmol) and PPh₃ (13.6 g, 51.8 mmol) in 100 ml dry toluene was stirred for 30 minutes at 80 degree before 6, 13-pentacenequinone (2.464 g, 8.0 mmol) was added in one portion and the solution was heated to reflux for 20 h. The reaction mixture was cooled to room temperature； the solid was removed by filtration and washed with toluene. The filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was triturated with ethanol and filtered to give pure product (4.10 g) in 86％yield.

Step (2) : Preparation of 6, 13-bis (diphenylmethylene) -6, 13-dihydropentacene (R-DHP) To a solution of 6, 13-bis (dibromomethylene) -6, 13-dihydroanthracne (2.575 g, 5 mmol) and aryl boronic acid (30 mmol) in 100 mL of toluene was added 2 mL ethanol and 2 mL water. The solution was stirred at room temperature and bubbled with nitrogen for 30 minutes. Then K₂CO₃ (5.520 g, 40 mmol) and (Ph₃P) ₄Pd (0.230 g, 0.200 mmol) were added and the mixture was heated to reflux. After 24 hours, TLC (50: 50 CH₂Cl₂-hexanes, UV) showed a new spot at R_f＝0.49. The reaction mixture was cooled to r.t. and the toluene was removed by rotary evaporator. The residue was poured into water and extracted with CH₂Cl₂. The organic layer was dried over MgSO₄, filtered and the solvent was removed by rotary evaporator. The product was purified by flash chromatography on silica gel column using 35:65 CH₂Cl₂-hexanes as eluent.

6, 13-bis (diphenylmethylene) -6, 13-dihydropentacene (BDPM-DHP) :

Similary, the compound was obtained as white solid (2.29 g) in 98％yield.

6, 13-bis (di-4’ -methoxylphenylmethylene) -6, 13-dihydropentacene (ADHP) :

Similary, the compound was obtained as white solid (2.360 g) in a yield of 75％.

6, 13-bis (di-4’ -methylphenylmethylene) -6, 13-dihydropentacene (TDHP) :

Similary, the compound was obtained as white solid (2.490 g) in a yield of 88％.

Example 5

Preparation of Nanoaggregates

Stock THF solutions of said molecules with a concentration of 0.1 mM were prepared. An aliquot (1 mL) of this stock solution was transferred to a 10 mL volumetric flask. After adding an appropriate amount of THF, water was added dropwise under vigorous stirring to furnish a 10 mM THF–water mixture with a specific water fraction. The water content was varied in the range of 0–99 vol％. Absorption and emission spectra of the resulting solutions and aggregates were measured immediately after the sample preparation.

Example 6

Photochromic Effect Testing

Colorless needle shaped crystals of BDPM-DHT exhibit blue emission under UV lamp irradiation (365nm) . The colorless crystals became red when the UV lamp was removed. Even in a very short irradiation time (～1 second) , obvious color change can be observed. Meanwhile, the blue emission significantly faded. When placed under room light for several minutes, the red crystals were gradually returned to colorless accompanied with blue emission recovery. Integrating the absorption and emission behaviors, BDPM-DHT crystals exhibit novel photochromic effects. When placed in darkness at room temperature for 2 days, the red crystals remained unchanged, indicating that they are thermally irreversible which is indispensable to the application as optical memories and switches for a photochromic system. Even placed at elevated temperature about 60℃ before the crystal collapse, the red crystals can survive for several hours in darkness. After cracking the red crystals, the colorless inner part told us that the photochromism occurred only on the crystal surface. Further prelonging the UV irradiation time to 10 minutes, the inner part keeps unreacted, which may be attributed to the UV absorption of red crystal surface.

Table 1 Relative energy^a, LUMO-HOMO gap, absorption edge and energy levels of LUMO and HOMO for BDPM-DHA, BDPM-DHT and BDPM-DHP.

Table 2. Crystal data and structure refinement summary.

KEY FEATURES

As can be seen from the foregoing examples, the present invention provides a series of novel polycyclic molecules bis (diarylmethylene) -dihydroacenes with aggregation-induced emission characteristics and their applications for organic photochromic materials.

Although the invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and the scope of the claim appended hereto.

Claims

an AIE compound is selected from the following formula (I) to (III) :

wherein each Ar is independently selected from:

Wherein,

R is independently selected from H, halo, hydroxyl, alkyl, alkoxy, alkenyl, alkynyl, acetyl, aryl, heteroaryl, cycloalkyl, heterocycloalkyl, or heteroalkyl that is optionally substituted.
According to the AIE compound of Claim 1, wherein the said Ar is independently selected from:
According to the AIE compound of Claim 1 or Claim 2, wherein the said Ar is independently selected from:
According to the AIE compound of and of Claims 1-3, wherein R is independently selected from H, halo, C_1-6 alkyl, C_1-6 alkoxy, C_1-6 alkylthio, NO₂, CN, OH, NH₂, C_1-6 monoalkylamino, C_1-6 dialkylamino.

More preferred, R is independently selected from H, C_1-4 alkyl, C_1-4 alkoxy, C_1-4 alkylthio, NO₂, CN, OH, NH₂, C_1-4 monoalkylamino, C_1-4 dialkylamino.
According to the AIE compound of any of Claims 1-4, wherein the AIE compounds are selected from the following formula (I’) to (III’)

Wherein, Ar is defined as any of Claims 1-4.

More preferred, the AIE compounds are selected from the following formula (I”) to (III”)

the most preferred AIE compounds are selected from the following:
A method for preparing the compound (I) - (III) of any of Claims 1-5, which comprises the following steps:

(1) Corey-Fuchs reaction: using triphenylphosphine and carbon tetrabromide to afford tetrabromo precursors,

(2) Suzuki-Miyaura reaction: using K₂CO₃ and Pd (PPh₃) ₄ led to the final products, optionally, purifying by recrystallization from chloroform-hexane without column chromatography.
According to the method of Claim 6, the method comprises:

(1) a mixture of CBr₄ and PPh₃ in dry solvent (such as toluene) was stirred at room temperature before formula (I-1) , (II-1) or (III-1) was added in one portion and the solution was heated to reflux, then formula (I-2) , (II-2) or (III-2) was obtained.

More preferred, the step (1) also contains the following step: the reaction mixture in step (1) was cooled to room temperature； the solid was removed by filtration and washed with solvent (such as toluene) .

Further more preferred, the step (1) also contains: the filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was triturated with solvent (such as ethanol) and filtered to give pure product.

(2) To a solution of formula (I-2) , (II-2) or (III-2) and aryl boronic acid in solvent (such as toluene) was added the mixed solvent (such as ethanol and water) . The mixture was stirred at room temperature and bubbled with nitrogen. Then K₂CO₃ and Pd (PPh₃) ₄ were added and the mixture was heated to reflux, then the product of formula (I) , (II) , (III) .

More preferred, the step (2) also contains the following step: the reaction mixture was cooled to room temperature and filtered through a pad, washing with organic solvent (such as dichloromethane) until the filtrate was clean.

Further more preferred, the step (2) also contains: the filtrates were concentrated under reduced pressure and the crude product was obtained. The crude product was then triturated with ethanol and filtered to give product.
According to the method of Claim 6, the method comprises the following steps:

Wherein, Ar is defined as any of Claims 1-5.
a method of applications of bis (diarylmethylene) -dihydroacenes of any of Claims 1-5 for organic photochromic materials.
a method of applications of bis (diarylmethylene) -dihydroacenes of any of Claims 1-5 with organic photochromic properties in light-emitting diodes, optical amplifiers, optical information storage, liquid crystal displays and bio-sensing, logic gates, nondestructive readout, and biological probes.