Mechanochromism and aggregation-induced emission directed by donor strength in quinoxaline-based D–A molecules with application in latent fingerprinting and inkless writing

Abstract

The molecular structure influences essential properties such as photoluminescence, charge transfer, and mechanical responsiveness, directly impacting material performance in optoelectronics, sensing, and bioimaging. The present work is a systematic effort to develop three organic molecules (QPA1, QPA2 and QPA3) having a donor–acceptor construct, wherein the charge transfer (CT) states were augmented with an aggregation-induced emission (AIE) effect. The synthesized molecules feature an aminophenyl group as the donor and formylated quinoxaline core as the acceptor. The variations in the donor strength on the aminophenyl core, from –H (QPA1) and –Me (QPA2) to –Ph (QPA3), profoundly and intricately modulated the AIE attribute as well as the CT states. QPA1 turns out to be an aggregation-caused quenching (ACQ) fluorophore, while QPA2 and QPA3 behave as AIEgens, with QPA3 showing superior efficiency. Furthermore, the charge transfer properties are modulated by donor strength, with QPA3 demonstrating a more pronounced intramolecular charge transfer response. QPA1–QPA3 molecules have significant solid–state emission and have shown mechanofluorochromic (MFC) behaviour in response to mechanical stress. The MFC response varies with the change in substituents. The excellent AIE activity of QPA3 has enabled its exploration for latent fingerprinting with three levels of detailing. The good contrast and brightness in the solid-state emission of QPA1 and QPA3 were further utilized for inkless writing application.