Harnessing a remote synergistic effect for regulating photoinduced electron transfer: a novel strategy for absorption/fluorescence dual-mode hydrochromism†

Herein, a remote synergistic effect has been proposed for effectively modulating the intramolecular photoinduced electron transfer (PET) process by unconventionally introducing two methyl groups into an amino group with the synergistic assistance of a neighboring auxiliary group. This strategy overcomes the problem of fluorescence quenching caused by PET without changing the electron-donating properties of the group which is important for retaining the original properties of molecules/probes. Benefiting from this strategy, an ideal absorption/fluorescence dual-mode hydrochromic molecular switch (i.e., dimethylamino-rhodamine (NMe₂-RhB)) is obtained. The involved hydrochromism and PET modulation mechanism were confirmed through detailed experiments and theoretical calculations. The NMe₂-RhB exhibited excellent water-induced color and fluorescence in both solution and a solid matrix, and its potential application in advanced anti-counterfeiting was demonstrated. This work not only provides a new dual-mode hydrochromic material, but more importantly, also offers new insights for regulating PET processes.