Synthesis And Excited State Properties Of Multifunctional Organic Light-emitting Materials Based On 9,9-Fluorene Derivatives

In recent years,organic light-emitting materials have been favored by researchers due to their abundance,environmental friendliness and functional diversification.The unique luminescent properties make it have broad application prospects in display,anti-counterfeiting,sensing and biological imaging.However,the specific relationship between chemical structure and excited-state luminescence properties is still not yet clear,and pure organic luminescence materials with excellent luminescence properties need to be developed urgently.In the process of designing organic lightemitting molecules,fluorenes with unique biphenyl structure are widely used due to their advantages of low price,stable structure and feasiable modifiability.In this work,a series of asymmetric diarylsubstituted fluorene derivatives were synthesized by Friedel-Crafts reaction and Pd(0)-catalyzed CH coupling reaction by taking advantage of the strong modifiability of the 9-position C of fluorenyl,and their comprehensive luminescence properties were investigated.The effects of heavy atom effect and steric hindrance effect on the excited state luminescence properties of materials were investigated.The main research contents are list as follows:1.By using the chemical modification strategies of conjugation interruption of fluorenone,oxygen atom bridging and nitrogen heterocyclic substitution,the differences of 9-site C asymmetric diaromatic cyclization substitution reactions were studied by Friedel-Crafts reaction and Pd(0)-catalyzed C-H coupling reaction.The experimental results show that: 9,9-bis(4-ethoxyphenyl)-fluorenol(F-2EPh)could be generated from 9-(4-ethoxyphenyl)-9-fluorenol(FPh-OH)and 9-(4-ethoxyphenyl)-9H-fluorene(FPh-H)through Friedel-Crafts reaction and Pd(0)-catalyzed C-H coupling reaction with the yields of 76% and 69%,respectively.The isolated electrons on the pyridine ring nitrogen atom,the spatial non-planation effect of fluorene conjugate structure interruption and oxygen atom bridging increase will hinder the formation of carbon negative center ions,and the subsequent bis(2-ethoxylbenzene)cyclization can not be carried out.The work provides important reference value for expanding the types of organic luminescent material substrates.2.In order to study the effects of heavy atom effect of bromine and steric hindrance effect of fluorene on the general excited state properties of multifunctional luminescent materials,we use typical room temperature phosphorescent luminescent material 9-(2-cyanophenyl)carbazole(OCz Ph CN)as reference.A series of diaryl fluorene derivatives Br Cz Ph CN,FCz Ph CN,Br FCz Ph CN and 2FCz Ph CN were synthesized by Friedel-Crafts reaction and C-H coupling reaction catalyzed by Pd(0).The results showed as follow: The 5% weight loss temperatures of OCz Ph CN,FCz Ph CN and 2FCz Ph CN are 248,369 and 447 ℃,respectively.There is no glass transition temperature of OCz Ph CN,and the glass transition temperature of FCz Ph CN and2 FCz Ph CN are 95 and 162 ℃,respectively.The thermal stability and film forming performance of FCz Ph CN and 2FCz Ph CN are better than that of reference compound OCz Ph CN,which is attributed to the increase of fluorene units.The maximum emission wavelengths of OCz Ph CN,FCz Ph CN and 2FCz Ph CN in toluene solution are 388 nm,399 nm and 400 nm,respectively,which belong to blue light emission.The singlet energy levels of OCz Ph CN,FCz Ph CN and 2FCz Ph CN powders are 3.35,3.04 and 3.04 e V,the triplet energy levels are 2.49,2.99 and 3.01 e V,and ΔEST are0.86,0.05 and 0.03 e V,respectively.The introduction of fluorene unit decreases the singlet energy level of the material,increases the triplet energy level of the material,and reduces the ΔEST of the material.The phosphorescent lifetimes of OCz Ph CN,Br Cz Ph CN,FCz Ph CN,Br FCz Ph CN and2 FCz Ph CN powders are 2.80 μs,1.33 μs,3.03 μs,2.69 μs and 2.56 μs,respectively.The PLQY of these powders are 20.17%,5.43%,30.75%,3.27% and 23.56%,respectively.The fluorescence quantum efficiencies of OCz Ph CN,FCz Ph CN and 2FCz Ph CN powders are 18.28%,29.05% and18.19%,respectively.The phosphorescent quantum yields are 1.89%,1.70% and 5.37%,respectively.The phosphorescence life and PLQY of fluorene modified FCz Ph CN are improved compared with OCz Ph CN at powder state,while the phosphorescence life and PLQY of Br Cz Ph CN containing bromine are shorter than OCz Ph CN.OCz Ph CN,Br Cz Ph CN and FCz Ph CN powders have obvious phosphorescence properties at room temperature.Blue light is emitted after uv lamp excitation at room temperature,and yellow afterglow of about 1.5,1.0 and 2.5 s can be observed after the lamp is turned off,respectively.Bromine atoms shorten their afterglow lifetime,while mono-substituted fluorene units increase the afterglow of FCz Ph CN powders.3.We take OCz Ph CN as the basic unit,increase the conjugated length to obtain its dimer DCz Ph CN,and introduce the hindrance group fluorene at the 3 and 3’ position of DCz Ph CN to obtain DFCz Ph CN.The experimental results show that the 5% weight loss temperatures of DCz Ph CN and DFCz Ph CN powders are 459 ℃ and 462 ℃,and their glass transition temperatures are 129 ℃ and 141 ℃,respectively.Both materials have good thermal stability and film forming properties.The emission wavelengths of DCz Ph CN and DFCz Ph CN in toluene solution are 411 nm and 422 nm,respectively.The singlet energy levels of DCz Ph CN and DFCz Ph CN powders are 2.98 e V and 2.95 e V,respectively,the correspoinding triplet energy levels are 2.77 and 2.81 e V,respectively,and ΔEST are 0.21 and 0.14 e V,respectively.The steric resistance effect of fluorene unit increases the triplet energy level,and decreases the ΔEST of fluorene unit.The phosphorescence life of DCz Ph CN and DFCz Ph CN powder at room temperature are 2.64 μs and 2.99 μs,and PLQY are17.36% and 15.64%,respectively.The fluorescence quantum yields of DCz Ph CN and DFCz Ph CN powder states are 15.04% and 15.52%,respectively,and the phosphorescence quantum yields are2.32% and 0.12%,respectively.The introduction of fluorene units increases the room temperature phosphorescence lifetime of the DFCz Ph CN in powder state.