Structures and charge transport properties of selenosulflower and its selenium analogue selflower: computer-aided design of high-performance ambipolar organic semiconductors

A novel crystal structure of octaseleno[8]circulene (C16Se8, we named it selflower) was predicted on the basis of a sym-tetraselenatetrathio[8]circulene crystal (C16S4Se4, selenosulflower). The charge transport properties of selenosulflower and its selenium analogue of selflower as potential ambipolar materials were investigated by the density functional theory (DFT) coupled with the incoherent charge-hopping model. Insights into their geometric and electronic structures, frontier molecular orbitals, reorganization energies and transfer integrals, anisotropic mobilities as well as band structures of the two novel materials are provided in detail. The gap of the frontier molecular orbitals decreases when all sulfur atoms of C16S4Se4 are substituted by selenium, which improves the charge transfer efficiency. The predicted hole and electron mobilities of C16Se8 are 1.03 and 1.26 cm(2) V-1 s(-1), respectively. C16S4Se4 has a hole mobility of 0.49 cm(2) V-1 s(-1) and an electron mobility of 0.74 cm(2) V-1 s(-1). Both circulenes exhibit electron-dominated ambipolar performance. The small reorganization energy and larger transfer integral originating from the face to face pi-pi stacking lead to large charge mobility for the novel compound C16Se8. From the viewpoint of transfer integral, the electron coupling among the dominant hopping pathways indicates that the charge transport processes take place in the parallel dimers with p-p interaction. The two materials exhibit a remarkable angular dependence of mobilities and anisotropic behaviors. The newly designed selflower C16Se8 is a novel organic semiconductor and worth synthesizing.