CONTRIBUTIONS OF THE ELECTROSTATIC AND THE DISPERSION INTERACTION TO THE SOLVENT SHIFT IN A DYE-POLYMER SYSTEM, AS INVESTIGATED BY HOLE-BURNING SPECTROSCOPY

Persistent spectral holes burned in the system octaethylporphin in poly(styrene) exhibit a symmetrical broadening varying in a linear fashion upon application of a static electric field. This effect is due to permanent electric-dipole moments induced in the dye molecules by the electric matrix field.The average value of the dipole-moment difference between the excited and the ground state of the guest molecules, which can be deduced from the broadening, shows a distinct increase from the blue to the red edge of the inhomogeneous absorption band, thus reflecting the varying dye-matrix interaction for centers with different solvent shift. A detailed analysis of this variation in the framework of a microscopic theory, based on a recent publication by Laird and Skinner [J. Chem. Phys. 90, 3274 (1989)], leads to the conclusion that the solvent shift of the absorption lines and also the variation across the inhomogeneous band is largely dominated by the dispersion interaction. The electrostatic contribution to the line shift is smaller by about 2 orders of magnitude. © 1990 The American Physical Society.