Axially Chiral Organic Semiconductors for Visible-Blind UV-Selective Circularly Polarized Light Detection

Technologies that detect circularly polarized light (CPL), particularly in the UV region, have significant potential for various applications, including bioimaging and optical communication. However, a major challenge in directly sensing CPL arises from the conflicting requirements of planar structures for efficient charge transport and distorted structures for effective interaction with CPL. Here, a novel design of an axially chiral n-type organic semiconductor is presented to surmount the challenge, in which a binaphthyl group results in a high dissymmetry factor at the molecular level, while maintaining excellent electron-transporting characteristics through the naphthalene diimide group. Experimental and computational methods reveal different stacking behaviors in homochiral and heterochiral assemblies, yielding different structures: Nanowires and nanoparticles, respectively. Especially, the homochiral assemblies exhibit effective π-π stacking between naphthalene diimides despite axial chirality. Thus, phototransistors fabricated using enantiomers exhibit a high maximum electron mobility of 0.22 cm² V^-1 s^-1 and a detectivity of 3.9 × 10¹² Jones, alongside the CPL distinguishing ability with a dissymmetry factor of responsivity of 0.05. Furthermore, the material possesses a wide bandgap, contributing to its excellent visible-blind UV-selective detection. These findings highlight the new strategy for compact CPL detectors, coupled with the demonstration of less-explored n-type and UV region phototransistors.