Atomic Chalcogen Substitution Modulates Photophysical Properties and Electronic Structure in Donor–Acceptor Covalent Organic Frameworks

Le résumé fourni par la source

While chalcogen substitution has recently emerged as a means for tuning the properties of covalent organic frameworks (COFs), its influence on the intrinsic photophysical and charge-transport properties of isoreticular donor–acceptor COFs remains largely unknown. Here, an isoreticular series of novel donor–acceptor COFs was constructed from a tetrathienonaphthalene-based (TTNTA) node and linear donor–acceptor–donor linkers containing oxygen (O), sulfur (S), or selenium (Se) within their acceptor cores. Highly crystalline COFs with identical topology and comparable structural order were obtained, while the synthesis of preferentially oriented thin films enabled direct comparison of chalcogen-dependent optoelectronic properties. Time-resolved photoluminescence measurements revealed progressively shorter emissive-state lifetimes from the O- to the S- and Se-containing COFs. Optical-pump terahertz-probe spectroscopy showed a parallel decrease in effective charge-carrier mobility across the same series, with the O-containing COF exhibiting the highest value of 0.19 ±0.02 cm 2 V −1 s −1 . Density functional theory (DFT) and time-dependent DFT calculations further revealed that valence-band dispersion originates from coupling between TTNTA- and linker-derived states and that the low-energy absorption involves linker-centered mixed excitations with progressively decreasing oscillator strength from O to Se. Collectively, these findings establish systematic structure–property relationships between acceptor-core chalcogen substitution and the photophysical and electronic properties of donor–acceptor COFs, providing mechanistic insights into their composition-dependent behavior and guidance for the design of future COF-based semiconductors.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.