A proton-assisted AIE active luminescent material having tunable emission in solution and solid state for anti-counterfeiting application: smart high contrast on-off-on fluorescence switch

The development of stimulus-responsive organo-luminogens having high solid-state emission, particularly in the near-infrared (NIR) region, is still demandable. Here, a newly designed and characterised aggregation-induced emission (AIE)-active luminophore, (4-hydrazonomethylphenyl)diphenylamine (DPABHz) exhibits a dual state emission nature with the green emission in solution state via ICT and red fluorescence in a twisted structure of the molecule in the solid state by way of TICT coupled AIE. Interestingly, the turn-on red emission in the solid state of DPABHz upon illumination with acid vapour through protonation via TICT was observed, although TICT is generally in favor of quenching. A detailed theoretical calculation has been performed to support all the attractive phenomena. This material could be used as a good acid-base switch in anti-counterfeiting applications.