给/吸电子基团取代对PPV类电致发光聚合物光电特性的影响

用量子化学的AM1和EHMACC/CO方法计算PPV,MEH-PPV和CN-PPV的电子和能带结构,讨论了烷氧基(-OR)和氰基(-CN)侧基取代对PPV类电致发光聚合物光电特性的影响.计算结果表明:给电子基团(-OR)取代使聚合物的HOCO(最高占据晶体轨道)能级升高,电离势减小,而吸电子基团(-CN)取代使LUCO(最低未占据晶体轨道)能级降低,电子亲和势增大,两者都使聚合物能隙降低,同时使聚合物的导电类型由PPV的p型转变成CN-PPV的n和p兼容型.该结果解释了MEH-PPV和CN-PPV光谱的红移及CN-PPV高的电致发光效率,为设计新型高效的PPV类电致发光聚合物提供了理论基础.

Influence of Donor/Acceptor Substitutions on the Properties of Photo-electricity in PPV-like Electroluminescent Polymers

The electronic properties and energy band structures of PPV, MEH-PPV and CN-PPV were calculated by quantum chemistry method, AM1 and EHMACC/CO, respectively. The influence of photo-electricity on PPV-like electroluminescent polymers substituted by alkyloxy(-OR) and cyano(-CN) were discussed. The result indicates that HOCO level(highest occupied crystal orbital) of polymer is raised by electron-donor(-OR) substitutions and the ionization potentials is decreased, while LUCO level(lowest unoccupied crystal orbital) is lowered by the electron-acceptor(-CN) substitution and electron affinities is increased. The band gap of polymer is decreased in both cases. At the same time, conducting type is changed from p type of PPV to n and p compatibility type of CN-PPV. The red shift of spectrum of MEH-PPV and CN-PPV and the higher electroluminescence efficiency of CN-PPV were explained. Our calculation is significant for designing new type PPV-like polymers with a high electroluminescence efficiency.