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

Abstract

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 cm² V⁻¹ s⁻¹, respectively. C₁₆S₄Se₄ has a hole mobility of 0.49 cm² V⁻¹ s⁻¹ and an electron mobility of 0.74 cm² 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 π–π 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 π–π 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.