Electronic properties of silole-based organic semiconductors

We report on a detailed quantum-chemical study of the geometric structure and electronic properties of 2,5-bis(6′-(2′,2″-bipyridyl))-1, 1-dimethyl-3,4-diphenylsilole (PyPySPyPy) and 2,5-di(3-biphenyl)-1,1-dimethyl-3, 4-diphenylsilole (PPSPP). These molecular systems are attractive candidates for application as electron-transport materials in organic light-emitting devices. Density Functional Theory (DFT), time-dependent DFT, and correlated semiempirical (ZINDO/CIS) calculations are carried out in order to evaluate parameters determining electron-transport and optical characteristics. Experimental data show that PyPySPyPy possesses an electron-transport mobility that is significantly greater than PPSPP, while PPSPP has a significantly larger photoluminescence quantum yield; however, the theoretical results indicate that the two systems undergo similar geometric transformations upon reduction and have comparable molecular orbital structures and energies. This suggests that intermolecular interactions (solid-state packing, electronic coupling) play significant roles in the contrasting performance of these two molecular systems.