Photoinduced Proton-Transfer-Mediated Molecular Recognition in Molecular Crystals

Molecular recognition has traditionally been focused on ground-state interactions. However, leveraging photoenergy to access excited-state molecular recognition, which may enable enhanced sensitivity or selectivity that is unattainable in the ground state, remains underexplored. In this study, we demonstrate a novel photoinduced molecular recognition mechanism using self-assembled crystalline microribbons composed of a donor-acceptor (D-A) molecule with a twisted molecular backbone for ultratrace phenol vapor detection. We confirm that photoinduced proton transfer occurs from phenol to the C═N group in the pyridine moiety of the D-A system, generating a protonated D-A molecule and a phenoxide ion that triggers fluorescence quenching. This proton-transfer-mediated recognition mechanism endows the microribbons with exceptional sensitivity and selectivity toward phenol vapor, achieving a limit of detection (LOD) of 0.6 parts per trillion (ppt). Our findings reveal that harnessing light energy to drive molecular recognition opens new avenues for advancing fluorescence sensing technologies.