Reversible Fluorescence Modulation in a Dyad Comprising Phenothiazine Derivative and Spiropyran

Abstract

AbstractWith the objective of developing fluorescent switch molecule, we have designed, synthesized and photophysically characterized a novel fluorophore‐photochrome dyad molecule comprising Phenothiazine derivative (PTCN, 4) and photochromic spiropyran (SP, 6). We successfully demonstrate that the photochromic behaviours of spiropyran unit regulate the fluorescence behaviours of phenothiazine derivative in terms of change in fluorescence intensity in PTCN‐SP(8) dyad in the solution as well as in the solid state by employing steady state spectroscopic techniques. The as prepared PTCN‐SP(8) is strongly fluorescent with fluorescent quantum yield more than 10% and regards as fluorescent “on” state. The spiropyran ring of photochrome (SP) opens up forming isomeric conformer, known as marocyanin (MC), upon UV irradiation in the dyad. This photogenerated isomer (MC) acts as an energy acceptor for PTCN fluorophore and energy transfer occurs from PTCN to MC via Förster resonance energy transfer (FRET) mechanism which leads to quench the fluorescence of PTCN and it is assigned to fluorescent “off” state. Subsequent visible light irradiation or thermal stimulation to the dyad is accompanied by ring close isomer SP along with complete reversal of the characteristic fluorescence of the PTCN(4), fluorescent “on” state. As a result, the photoinduced reversible transformations of the photochromic component within the dyad effectively bring “on” and “off” states of the PTCN fluorescence emission. Indeed, the fluorescence of this photoswitchable dyad is modulated for several cycles with excellent fatigue resistance under optical control for both in solution and solid phases. Thus, the choice of PTCN(4) as fluorescent probe in the dyad can ultimately lead to the development of valuable photoswitchable fluorescent probe for device applications.