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

RESEARCH ARTICLE www.advancedscience.com Axially Chiral Organic Semiconductors for Visible-Blind UV-Selective Circularly Polarized Light Detection Yejin Kwon, Je-Yeon Jung, Won Bo Lee,* and Joon Hak Oh* 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–𝝅stacking 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. 1. Introduction CPL plays a pivotal role in various advanced applications[1] including optical quantum computing,[2] encrypted communications,[3] and bioimaging.[4] In these domains, the need for CPL detectors that can selectively distinguish between the two polarization states of CPL is crucial. A con- ventional method to detect CPL involves the use of silicon Y. Kwon, J.-Y. Jung, W. B. Lee, J. H. Oh School of Chemical and Biological Engineering Institute of Chemical Processes Seoul National University 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea E-mail: wblee@snu.ac.kr;joonhoh@snu.ac.kr The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/advs.202308262 © 2024 The Authors. Advanced Science published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. DOI: 10.1002/advs.202308262 photodetectors combined with additional optical apparatus, that is, a linear po- larizer and a phase retarder. However, there is a growing necessity for mate- rials capable of directly and inherently sensing CPL without requiring additional apparatus. Such materials are essential for advancing the development of minia- turized and integrated CPL detectors. Researchers have explored various CPL- responsive materials,[5] encompassing inorganic nanomaterials,[6] chiral organic small molecules, polymers,[7] and hybrid organic-inorganic perovskites.[8] Among them, organic semiconductors exhibit distinct advantages over other materials due to their intrinsic chirality, lightweight, cost-effectiveness, and the ease with which their chiroptical properties can be tailored through rational molecular design. To date, several approaches have been reported to fabricate organic CPL detec- tors, such as blending achiral polymers with chiral small molecular additives,[9] ampli- fying chirality by supramolecular or mul- tiscale assemblies,[10] and utilizing twisted molecules.[11] However, there is an in- evitable trade-offbetween charge trans- port properties and CPL selectivity, as the former requires planar 𝜋-stacked structures while the la