Constructing Chiral Covalent‐Organic Frameworks for Circularly Polarized Light Detection

RESEARCH ARTICLE www.advmat.de Constructing Chiral Covalent-Organic Frameworks for Circularly Polarized Light Detection Qianfeng Gu, Jiajia Zha, Cailing Chen, Xin Wang, Wenyan Yao, Jiahe Liu, Fangyuan Kang, Jinglun Yang, Yang Yang Li, Dangyuan Lei, Zhiyong Tang,* Yu Han,* Chaoliang Tan,* and Qichun Zhang* The use of chiral covalent organic frameworks (COFs) as active elements in photodetectors to directly identify circularly polarized light (CPL) can meet the requirement of integration and miniaturization of the as-fabricated devices. Herein, the design and synthesis of two isoreticular chiral two-dimensional (2D) COFs (CityU-7 and CityU-8) by introducing photosensitive porphyrin-based amines (5,10,15,20-tetrakis(4-aminophenyl)porphyrin) to enhance the optical absorption and chiral aldehyde linkage (2,5-bis((S/R))-2-methylbutoxy)terephthalaldehyde) to engender chirality for direct CPL detection are reported. Their crystalline structures were confirmed by powder X-ray diffraction, Fourier-transform infrared spectroscopy, and low-dose transition electron microscopy. Employing both chiral COFs as the active layers in photodetectors, left-handed circularly (LHC) and right-handed circularly (RHC) polarized light at 405 nm can be well distinguishable with short response time, high responsivity, and satisfying detectivity. The study provides the first example on the design and synthesis of chiral COFs for direct detection of CPL. 1. Introduction The detection of circularly polarized light (CPL) plays an indispensable role in many applications including quan- tum computation,[1–2] optical communication,[3–4] magnetic recording,[5–6] security system,[7–8] remote sensing,[9] and sub- stance screening.[10] Thus, effectively distinguishing two states of CPL (left- and right-handed rotation) in a cost-efficient way Q. Gu, J. Zha, X. Wang, J. Liu, F. Kang, J. Yang, Y. Y. Li, D. Lei, Q. Zhang Department of Materials Science and Engineering City University of Hong Kong Tat Chee Avenue 83, Kowloon, Hong Kong, SAR 999077, P. R. China E-mail: qiczhang@cityu.edu.hk C.Chen,Y.Han AdvancedMembranes andPorous Materials (AMPM)Center Physical ScienceandEngineering Division King Abdullah University of ScienceandTechnology (KAUST) Thuwal 23955–6900,Saudi Arabia E-mail: yu.han@kaust.edu.sa The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202306414 DOI: 10.1002/adma.202306414 becomes a key technology. Although left- handed circularly (LHC) and right-handed circularly (RHC) polarized light can be identified through an achiral photodetector integrated with a quarter-wave plate and a polarizer, the absence of intrinsic chi- roptic properties in photoactive materials requires the additional optical components and the complicate processing, which imposes huge challenges to future CPL detectors in terms of miniaturization and flexibility. Thus, constructing photode- tectors with chiral materials as optically active elements to directly detect LHC and RHC is necessary.[11–12] Although several types of chiral materials includ- ing organic compounds,[13–14] plasmonic nanoparticles,[12,15] and chiral hybrid perovskites[11,16–17] have been employed in chiral photodetectors, their obvious disad- vantages such as strong electron–photon coupling and low exciton dissociation energy can result in nonradiative recombination pathway and low responsivity of photodetection.[11,18] Besides, the high cost may limit the practical application of plasmonic nanoparticles while the toxic Pb element in hybrid perovskites may cause sev- eral safety and health problems. To address these issues, chiral covalent-organic frameworks (COFs) with unique chirality fea- tures and order porous structure might be a good choice for ef- ficient light trapping because the array of chiral centers not only W. Yao, Z. Tang CAS Key Laboratory of Nanosystem and Hierarchical Fabrication CAS Center for Excellence in Nanoscience National Center for