Excited state intramolecular proton transfer process in benzazole fluorophores tailored by polymeric matrix: A combined theoretical and experimental study

Abstract

The effects of the polymeric matrix on the photophysical properties of monomeric dyes reactive to Excited State Intramolecular Proton Transfer (ESIPT) were evaluated by UV–Vis absorption and steady-state and time-resolved emission spectroscopies. A radical polymerization reaction was used to produce new photoactive styrene-based polymeric matrices. The fluorescent polymers had their structural, thermal, electrochemical and photophysical properties evaluated. The benzazole monomers presented excited-state properties dependent on the viscosity induced by the polymeric media, wherein only the ESIPT process extension was unfavoured once the species stability in the excited state did not vary, as observed in the analysis of their fluorescence lifetimes when diluted in organic solvent. Additional experiments performed in the highly viscous non-polar aprotic solvent Nujol, as well as theoretical predictions by the analysis of the energy barriers relative to both the excited state reaction and rotational conformers, performed at the CAM-B3LYP/6–311 + G(d,p) level of theory corroborate these observations. The theoretical calculations showed that the activation energies relative to the conformational balances in the excited state were extremely increased in comparison to those on the ground state, indicating that viscosity is a significant driving force to the ESIPT process.