Theoretical Studies On Electronic Structures And Photoelectric Properties Of Silole-based Derivatives

Since the first synthesis of silole (1,1,2,3,4,5-hexaphenylsilole) by Braye and Hübel, there have been extensive studies on the synthesis, reactivities, properties and coordination abilities of such compounds to transition metals, silole ring polymers, the aromaticity of their anionic or cationic species and silole ring as a new building unit inπ-conjugated. Low lying LUMO level, lager electron affinity and very high electron mobility of the silole make siloles as ideal candidates for applications at emitting and electron-transporting (ET) materials in light-emitting devices (LEDs).In the present study, we performed theoretical studies on the geometrical structure, electronic structure, spectral properties of 1,1-disubstituted-3,4-dimethyl-2,5- bis(trimethylsilyl)siloles. The theoretical results showed that the excitated transition type was theπ→π*, and the structural relaxation of the excitated state was mainly localization on the silole ring and its 2,5-substituent groups. Due to the electronegative difference of substituent groups, the changes of the ground-state and excitation geometry, the energy gap between HOMO and LUMO, absorption and emission wavelengths for five compounds occurred, that is, more electronegative 1,1-substituents tend to give lower energy gap between HOMO and LUMO, longer absorption and emission wavelengths.We also performed theoretical studies on the geometrical structure, electronic structure, absorption and emission wavelengths of siloles, in which the different positions of silole ring were substituted by methyls and phenyls, respectively. The excitated transition type was theπ→π*, and the structural relaxation of excitated state was mainly localization on the silole ring and its 2,5-substituent groups. The absorption peak of silole-based derivatives substituted by 2,5-substituents are obviously red shifted compared with that of 1,1-substituents. The different substituents and different substituent positions will influence the energy levels of HOMO and LUMO. The LUMO level of silole substituted by phenyls was lower than that of by methyls at the same positions. Therefore, compared with the silole substituted by methyls, the ones substituted by phenyls were more suitable to be used as electron-transporting (ET) materials in light-emitting devices (LEDs).