A Proline‐Integrated Donor–Acceptor Fluorophore: Water‐Vapor‐Responsive Mechanochromic Luminescence and Latent Fingerprint Visualization

Despite the rapid growth of stimuli‐responsive fluorophores, unifying multiple orthogonal functions within a single small organic fluorophore remains a fundamental challenge. Herein, the integration of a donor–acceptor fluorophore with a chiral amino acid enables multifunctional luminescence. The resulting fluorophore exhibits an unusual water‐vapor‐responsive mechanochromic luminescence (MCL), in which emission recovery is triggered by water vapor rather than by organic solvent vapors or thermal treatment, in contrast to typical MCL systems. Owing to its molecular chirality, this MCL is accompanied by ON/OFF switching of solid‐state circularly polarized luminescence (CPL). The amphoteric proline unit additionally imparts acid‐ and base‐responsive luminescence switching. Furthermore, the amphiphilic and solvatochromic properties allow the fluorophore to function as an efficient aqueous probe for latent fingerprints, affording clear visualization of level 3 details with operational simplicity. This work provides a novel molecular design strategy for assembling versatile luminescent and sensing functions within a single organic fluorophore and advances the development of multifunctional luminescent materials.