8-羟基喹啉锂的光电性能和取代基效应的密度泛函理论

Theoretical Investigation on Photoelectric Properties and Substituent Effect of 8-hydroxyquinoline Lithium

采用密度泛函理论(DFT)较为系统地研究了给、吸电子取代基对8-羟基喹啉锂(Liq)光电性能的影响。研究结果表明:不同取代基与母体形成不同的共轭,取代基—CN、—OCH3很好地参与了整个π体系共轭,对体系性质影响较大;吸电子基—CF3、—CN、—Cl在5-位取代都使Liq的最高占据轨道(HOMO)、最低空轨道(LUMO)能级降低;给电子基—CH3、—CH3CH2CH2、—OCH3在5-位取代都使Liq的LUMO、HOMO升高,带隙减小,给电性越强,影响越显著;—CN在5-位取代,显著增加了Liq的电子亲和势,降低了电子重组能,使电子更易于注入和传输。与Liq及其它衍生物相比,5-CN-Liq是一种更好的电子注入和传输材料。

In this paper,the influences of electron donating and withdrawing substituents on photoelectric properties of 8-hydroxyquinoline lithium（Liq） are systematically studied by density functional theory（DFT）,several significant research results were achieved to provide theoretical guidance for further improving the performance of Liq.The research results showed that the different substituents form different conjugate with the parent population.The substituents of —CN,—OCH3 participate in the π-conjugated system properly,and have a great influence on the properties of the system.While the substituents of —CF3,—CH3,—CH3CH2CH2,—Cl have the weaker conjugated effects with the system,and relatively a little influence on the properties of the system is obtained.The electron donating substituents enhance O-Li electrostatic interaction and N-Li covalency,and the electron withdrawing substituents weaken O-Li electrostatic interaction and N-Li covalency.The electron withdrawing groups of —CF3,—CN,—Cl,which is attached to 5-position of Liq,make LUMO and HOMO energy level lower,but the dependence of the LUMO,HOMO and band gap on their inductive effect strength lack regularity.The —CF3,—CN broadens band gap of Liq,however the —Cl leads to band gap of Liq reducing.Here,the synergistic action of conjugated effects should be included.The electron donating groups of —CH3,—CH3CH2CH2,—OCH3 which is attached to 5-position of Liq,make LUMO and HOMO energy level rise and band gap contract,the stronger interaction between the substituent and the molecular orbital,the more remarkable the influence on the frontier molecular orbital.The —CN substitution at 5-position of Liq make the electron affinity significant increase,the reorganization energy decrease,so that electron injection and transport become more easy.It can be concluded that 5-CN-Liq is a kind of better electron injection and transport materials than Liq and other derivatives of Liq.