Vibronic resonance in spectra of frozen solutions of the C60 fullerene derivatives

This paper reports on a study by site-selective laser spectroscopy of low-temperature broadband fluorescence spectra of N-methyl-2-(3,5-di-tert-butyl-4-hydroxyphenyl)-C₆₀] fulleropyrrolidine (N-MBHPhFP fullerene) molecules embedded in the crystalline toluene matrix. It has been shown that monochromatic laser excitation in the region of vibrational satellites of the pure electronic absorption band initiates structurization of the emission band of a pure electronic transition, which suggests the existence of a set of impurity centers in the crystalline host matrix. An analysis has been made of the factors accounting for replacement of the wide, inhomogeneously broadened band by a series of narrow bands, with the most essential of them being the weakness of electron-phonon coupling in the impurity center, the absence of electronic excitation transfer between the centers, and the vibronic resonance in the excited state of the set of centers. Vibration frequencies of the N-MBHPhFP fullerene in the excited electronic state have been determined.