Synthesis,Structure And Photophysical Properties Of Novel Organic Boron-Carbon-Nitrogen Fluorescent Material

Organic photoelectric functional materials are mostly designed based on conjugated systems,because delocalized π-electrons respond more to external electromagnetic fields than a-electrons.Any structural modification can effectively adjust its π electron number and electron cloud distribution,and then regulate its energy level structure and photophysical properties.Introducing BN unit into the organic conjugated system based on carbon atoms can promote the intramolecular charge transfer by utilizing the electron effect and orbital interaction between heteroatoms and π conjugated system,thus realizing the regulation of the energy level structure and photoelectric properties of the whole molecule.Therefore,it is of great significance to introduce heteroatoms to construct a "hybrid" π-system.The boron and nitrogen elements are introduced into the π conjugate structure based on carbon atoms while maintaining the good coplanarity and rigidity of the molecular skeleton.The effect of BN instead of CC on the photoelectric properties of polycyclic aromatic hydrocarbons was studied from the perspective of embedding position,number and orientation of BN units.In this work,we have designed and synthesized totally 17 target compounds and 14 crystal structures of them were determined.The photophysical properties were systematically studied by analyzing their crystal structures and theoretical calculations.The contents and conclusions are as follows:1、Synthesis,structure and photophysical properties of NBN embedded indole-anthracenePolycyclic aromatic anthracene doped with NBN was efficiently synthesized by one-pot condensation reaction of boric acid and diamine.The compounds of NBN five-membered ring showed the luminescent properties of traditional luminescence,with remarkable fluorescence quantum yields in solution,up to 97%.However,the compounds of NBN six-membered ring were a new class of AIE molecules with aggregation-induced emission properties.In the crystal structure of compounds,the planarity of anthracene unit is better,while the substituent group on N in diazoboron unit affects the π-π interaction between molecules,which is the reason for the relatively high fluorescence quantum yield of compounds containing NBN asymmetric fivemembered rings.The experimental results showed that NBN compounds are very sensitive to solvent polarity and can specifically target lipid droplets.2、Synthesis,structure and photophysical properties of BNBNB embedded anthracene-fused fluorantheneA novel strategy of multi-boron doping was developed to introduce zigzag BNBNB structural motifs in polycyclic aromatic hydrocarbons by one-pot method,utilizing the indoletype N-directed C-H borylation reaction from NBN-embedded heterocyclic aromatic precursors.The single crystal structure of BNBNB compound was analyzed successfully.In the crystal structure,BNBNB-embedded anthracene-fused fluoranthene has a nearly perfect planar geometry,the conjugation degree of the whole compound is increased,accompanied by the obvious red shift of absorption and emission peaks.The BNBNB compound also showed sensitive response to solvent polarity and specific targeting to lipid droplets.3、Synthesis,structure and photophysical properties of dimesitylboryl-ended oligothiophene with tetrazine as coreThe reaction product of tetrazine-cyclooctene system is usually predicted as a dihydropyridazine derivative,there are few people found that it could be aromatized to a pyridazine compound.The crystal structure of iEDDA reaction products were successfully isolated using tetrazine and cyclooctene as raw materials.The results showed that they both were pyridazine derivatives,which confirmed the dehydrogenation of direct D-A produced dihydropyridazine derivative to an aromatized pyridazine compound under ambient conditions,and this is the first example of crystal structure of dehydrogenated tetrazine-cyclooctene product.In BTz,the tetrazine unit significantly quenches the molecular fluorescence,while the subsequent iEDDA reaction destroyed the tetrazine part,eliminated the corresponding dark state and turned on the bright fluorescence.Especially,the reaction kinetics of BTz with different dienophiles was studied.Among them,the reaction between BTz and(4E)-TCO-OH was the fastest,and the fluorescence was enhanced about 100 times.4、Exploration of novel boron-nitrogen doped pyrene derivativesTwo routes to synthesize novel BN-doped pyrene derivatives have been explored:one is to synthesize boron-nitrogen-doped pyrene compounds through photothermal conversion of four-coordinated boron-nitrogen compounds.The N,C-chelated boron compound B(PQ)Mes2 is a typical thermally reverse photoisomerized material.Under the irradiation of 365 nm ultraviolet light,the B-N bond in its molecular structure remained intact and a new C-C bond was formed between the benzene ring and the dearomatized mesityl.However,the C-C bond in the structure was broken and the structure was restored after thermal stimulation.The photothermal conversion rate of the compound was analyzed by 1H NMR,and the reason was analyzed from the perspective of structure,which provided reference for the subsequent molecular design of N,C-chelated boron compounds and the synthesis of pyrene derivatives.Another route is based on benzoquinoline as the synthesis platform,developed a new type of BN doping pyrene derivatives synthesis strategy.1,4-dimesityl-4,5-dihydro-1H-3a-aza-4borapyrene(BNP)was successfully synthesized by boron-silicon exchange reaction between BBr3 and alkyl silicon.This is the first example of boron-alkyl silicon exchange reaction and provides another feasible route for the subsequent synthesis of BN-doped pyrene.