Frequency dependence of the quadratic electron-phonon coupling constant in a polymer glass: Direct measurement by single-molecule spectroscopy

Abstract

The frequency dependence of the quadratic coupling constant between the electron system of the chromophores and the quasilocal vibrational modes of the matrix, $B({\ensuremath{\omega}}_{0})$, and its distribution was measured in a disordered system via single-molecule spectroscopy. A correlation between $B$ and ${\ensuremath{\omega}}_{0}$ was found which does not follow a power law. The analysis of this result allows us to suggest that, for a correct description of the broadening of optical impurity spectra in disordered solids, the applicability of the weak-coupling limit and the long-wavelength approximation should be considered separately for each single molecule interacting with its local environment. A simple formulation of the electron-phonon coupling theory for the dye-matrix system as a whole is, in general, not appropriate.