Recent advances in excited state intramolecular proton transfer mechanism-based solid state fluorescent materials and stimuli-responsive fluorescence switching
Stimuli-responsive organic solid state fluorescent materials are considered as potential candidates for optoelectronic application as well as in the biomedical field. Molecular design and supramolecular interaction controlled organization in the solid state played an important role in producing switchable and tunable fluorescent materials. Excited state intramolecular proton transfer (ESIPT) mechanism-based solid state fluorescent materials showed unique photophysical properties such as a large Stokes shift and local environment (pH, polarity, ions and viscosity) responsive fluorescence modulation. The unique photophysical properties of ESIPT molecules made them interesting for various fields including laser dyes, molecular probes, optoelectronics, white emissive materials and optical information storage materials. Systematic fluorophore structural engineering has been performed over the years to gain insight on the ESIPT mechanism in order to improve the quantum efficiency and introduce desirable material attributes for functional applications. The substitutional unit, molecular conformation and supramolecular interactions played a significant role in transforming planar ESIPT fluorophores to stimuli-induced fluorescence switching materials either between two states or off–on states. In this review article, we have presented the recent developments in ESIPT-based solid state fluorescent materials and external stimuli-induced fluorescence switching.