Spectral luminescent properties and dynamics of intramolecular processes in 2,4,5-triarylimidazoles

The excited-state intramolecular proton transfer (ESIPT) in some 2,4,5-triarylimidazoles (TAIs) is studied by the methods of steady-state luminescence and femtosecond laser absorption spectroscopy. It is found that ESIPT in 4,5-diphenyl-(2-hydroxyphenyl)imidazoles occurs both in solutions at ambient temperature and in glassy matrices at 77 K. In the case of 4,5-diphenyl-(2-hydroxynaphthyl)imidazole, a rotation of molecular fragments is necessary for ESIPT to occur, which results in the absence of ESIPT at 77 K. The characteristic times of intramolecular processes in the excited state of TAIs are measured by the method of femtosecond absorption spectroscopy. It is shown that the ESIPT time in TAIs depends on the molecular structure—it is extremely short (≤100 fs) in molecules with a planar reaction center and three times as long in TAIs with a non-planar reaction center—being determined by the time of conformational rearrangement.