Theoretical study on the photophysical properties of boron-fused double helicenes

Abstract

Heterohelicenes have attracted much attention because the involvement of heteroatom into helicene skeleton effectively modulates physical properties and greatly widens the application of helicenes. Recently, boron-fused double helicenes (compounds 1 and 2), exhibiting unique photophysical properties, were reported [J. Am. Chem. Soc., 2016, 138, 5210]. Fully understanding their microelectronic structures is rather important for further performance optimization or improvement. Here, we employed density functional theory to investigate the electronic transition properties, circular dichroism (CD), charge transport, and second-order nonlinear optical (NLO) response of the seven boron-fused double helicenes. Our simulated UV-vis/CD spectra of compound 2 are in good agreement with experimental ones. Different electron-donor or electron-acceptor substituents have considerable effect on frontier molecular orbital energy level, absorption wavelength, electron transition property, and second-order NLO response values. The designed compound 7 with two electron donors (TTF) and two electron acceptors (TCNQ) is expected to be excellent second-order NLO material in view of large first hyperpolarizability value and inherent asymmetric structure. The study of charge transport indicates that incorporation boron and oxygen atoms into intermolecular π–π packing units is an effective way to realize ambipolar charge transport.