Auxiliary Methoxy Aided Triphenylamine and Dicyanoisophorone Based Flurophores with Viscosity and Polarity Sensitive Intramolecular Charge Transfer

Abstract

Novel, multibranched “triphenylamine based donor with added auxiliary methoxy donor and dicyanovinyl acceptor” based fluorescent molecules are developed. The dicyanoisophorone moiety is used as a configurationally locked polyene system for π-conjugation linking between donor and acceptor, to control the unnecessary intramolecular rotations in the molecule, which can to act as a rotor. The synthesized dyes show good fluorescent molecular rotor properties and strong emission solvatochromism. Auxiliary methoxy donors shift both the absorption and emission maxima towards longer wavelengths compared to known analogues, along with increased Stokes shifts. Fluorescent molecular rotor properties of the dyes are influenced by a local excited state to twisted intramolecular charge transfer state transition, which is discussed in terms of emission solvatochromism and Lippert–Mataga, Weller and Rettig polarity plots. Three different viscous solvent systems i.e., paraffin oil–dichloromethane, polyethylene glycol-400–dichloromethane and polyethylene glycol-400–N,N-dimethylformamide are used to investigate the sensitivity of rotors towards the viscosity of the environment. A maximum 16-fold enhancement in emission intensity and 0.616 × value is achieved for rotor Dye-3. The polarity effect of a binary viscous solvent system, by the virtue of intramolecular charge transfer, on the viscosity sensing properties of rotors is explained by constructing the Weller and Rettig’s plots for different viscous systems.