Excited-state intramolecular proton transfer-based multifunctional solid-state emitter: a fluorescent platform with ‘write-erase-write’ function

摘要： The excited-state intramolecular proton transfer (ESIPT)-based molecular probes have drawn significant attention owing to their environment-sensitive fluorescence properties, large Stokes shift and emerged as building blocks for the development of molecular sensors and switches. However, most of the ESIPT-based fluorophores exhibit weak emission in the solid state limiting the scope of real-time applications. Addressing such issues, herein, we presented a C3-symmetric like molecular architecture employing a simple one-step Schiff base condensation between triaminoguanidinium chloride and 3,5-di-tert-butyl-2-hydroxybenzaldehyde (TGHB). The temperature-dependent fluorescence studies including at 77 K indicated the strong emission from the keto tautomer compared to that of the enol. The facile ESIPT in TGHB in the solid-state led to a remarkable enhancement of fluorescence quantum yield of 1600-times compared to that of the solution (λem = 545 nm) by restricting the intramolecular rotation and subsequently suppressing the nonradiative deactivation. The excited–state processes were further elucidated through time-resolved fluorescence measurements. TGHB exhibited turn on-off fluorescence upon exposure to acid /base vapor in the form of powder as well as transparent, free-standing thin film. A rewritable and erasable fluorescent platform was demonstrated using TGHB as molecular ink, which offers a potential testbed for performing multiple times ‘write-erase-write’ cycles. In addition, TGHB, possessing multiple binding sites (O and N donors) involving the central core of triaminoguanidinium cation, displayed selective turn-on fluorescence with Zn2+. The structure-property relationship revealed in the present study provides insight towards the development of novel cost-effective multifunctional materials promising for stimuli-responsive molecular switches.