Research On Synthesis And Performance Of Carbazole-based Organic Small Molecular Photoelectric Materials

Organic light-emitting materials have been attracting increasing attention owing to their unique properties and potential applications.Introducing long conjugated chain,elerton-donating groups,electro-withdrawing groups or rigid conjugated plane can effectively improve luminous performance of organic light-emitting materials.For gaining a kind of light-emitting materials with rigid conjugate flat plane,people usually adopt molecules with rigid conjugated plane and connect electron donors or electron acceptors in its skeleton by conjugated bridge.Besides,introduction of long alkyl chain can effectively block intramolecular electronic transition and improve solubility.Carbazole is a vitally important organic light-emitting materials with specific rigid plane structure,larger conjugate system and internal charge transfer capability.In addition,carbazole has excellent photoelectric properties and are easy to be modified.Therefore,it is often used as molecular skeleton in the design and synthesis of organic molecules with optoelectronic functions.The synthesis and application of carbazole derivatives with optoelectronic function have been attracted a great deal of attention of researchers.In this paper,carbazole with strong electron donating ability was used as important unit.Through various reactions,different functional groups were introduced in its 3,6,9 bits respectively,and three kinds of organic small molecular photoelectric materials were synthesized,namely ristriazolotriazine derivatives,tetraarylethene derivatives and cyanostilbene derivatives.Their struetures were characterized by NMR spectra and MS spectra.Their optical,thermal,electrochemical etal properties were studied.The main research results have shown asfollows:?1?A new molecule was designed and synthesised with the use of electron-donor carbazole unit and electron-acceptor TTT building blocks.The compound was used for cation detection for the first time based on photoinduced charge transfer?PCT?.The synthesised compound exhibits highly sensitive and significant fluorescence decline response towards Cu²⁺over other metal ions.The test showed a wide dynamic range from 0.2?M to 2 mM,with a detection limit of 0.2?M in THF-H₂O?9:1,v/v?at neutral pH.The compound also exhibits excellent selectivity in the presence of other common cations.Its optical,thermal,electrochemical and morphological properties were studied.The results demonstrate that the compound has high relative fluorescence quantum yield??_F=0.99?in xylene solution,excellent thermal stability?T_d=325°C,T_g=99.9°C?,wide energy gap?E_g=4.09 eV?,desirable triplet energy?E_T=2.98 eV?and the highest occupied molecular orbital energy?–5.67 eV?.Morphological investigation showed that the compound easily forms ribbon-like microstructures.?2?Multifunctional optoelectronic materials are important in both theoretical and practical application aspects.Hence,three luminogen-based N-phenylcarbazol-substituted tetraarylethene,namely NPCE,MeNPCE and MeONPCE,were designed and synthesised via Friedel–Crafts acylation and McMurry coupling reaction.All of the luminogens show typical aggregation-induced emission?AIE?characteristics with high solid-state efficiency of up to 83%.The dyes also exhibit excellent thermal stability?T_d of up to 434°C?and prominent morphological stability.In addition,only MeONPCE reveals obvious mechanochromism?emission wavelength change of up to 64 nm?.This proved that introducetion methoxy group in one of the phenyl rings at para position can easily obtain mechanochromic materials.The organic light-emitting diodes?OLEDs?that use these dyes as nondoped emission layer emit cyan light with current efficiency and external quantum efficiency of 7.87 cd A^-1 and 3.87%,respectively.In comparison,the mutilayer organic light-emitting diodes adopting MeONPCE as nondoped emission layer reveals that MeONPCE is an eximious p-type light emitter.?3?Five cyanostilbene derivatives containing carbazole 2a-2e were designed and synthesised via Vilsmeier-Haack reaction and Knoevenagel condensation reaction.They have twisted D–?–A structured and internal charge transfer effect.All of the luminogens show typical aggregation-induced emission?AIE?and crystallization-induced emission enhancement?CIEE?characteristics.The quantum yield of the crystalline particles is much higher than that of the amorphous particles.In addition,2a,2d and 2e reveal obvious mechanochromism behavior,with high contrast of up to119 nm.And the mechanochromism can be repeatedly switched many times without fatigue by simple grinding–annealing processes.2b and 2c have no such property because they provided with strong crystallizability crystallization capability to form stable crystals,such that the change from the crystalline to the amorphous phase cannot be realized.Meanwhile,the research of their crystal structure suggests that mechanochromism behavior is closely related with twisted angle of the molecule.