A didactic model of solvent shifts, inhomogeneous broadening, and linear and quadratic electron-phonon coupling

A simplified model of optical spectra of chromophores embedded in disordered solids is proposed. Using the repulsive-dispersive potentials of the ground state and the excited state in Lennard-Jones form the expressions are obtained for inhomogeneous site energy distribution function, and the linear and quadratic coupling strength of electronic transition to local phonons. Experimentally, the shift of spectral holes was studied for chlorin in polymer hosts at temperatures between 5 and 40 K and by applying hydrostatic He gas pressure up to 200 bar. The opposite frequency dependencies of line shifts induced by temperature and pressure are in agreement with the model, if the potential minimum of the excited state is shifted to a shorter distance.