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 structure-property relationship is fundamental in determining the performance and functionality of materials, as the molecular structure directly influences properties such as photoluminescence, mechanical responsiveness, and charge transfer, which are crucial for applications in areas like optoelectronics, sensing, and bioimaging. In this context, the present work relays a systematic effort to develop three organic molecules (QPA1, QPA2 and QPA3) having donor-acceptor construct wherein the charge transfer (CT) states have been augmented with aggregation induced emission (AIE) effect. The synthesized molecules feature an aminophenyl group as donor and formylated quinoxaline core as acceptor. The variation of donor strength on aminophenyl core from –H (QPA1), –Me (QPA2) to –Ph (QPA3) profoundly and intricately modulated the AIE attribute as well as CT states. QPA1 turns out to be an aggregation caused quenching (ACQ) fluorophore while QPA2 and QPA3 behave as AIEgens with later being more proficient. Further the CT characteristic also varies with the donor strength as QPA3 reveals superior intramolecular charge transfer. QPA1-QPA3 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 has enabled the exploration of QPA3 for latent finger printing with three levels of detailing. The good contrast and brightness in solid state emission of QPA1 and QPA3 have further been utilized for inkless writing application.