DIPOLE-MOMENT DIFFERENCES OF NONPOLAR DYES IN POLYMERIC MATRICES - STARK-EFFECT AND PHOTOCHEMICAL HOLE BURNING .1.

The difference of the induced dipole moments DELTAmu(ind) between the ground and excited state of (centro-)symmetric dye molecules (tetraphenylporphin and tetrapropylporphycene) embedded in different nonpolar and polar polymers is investigated. The technique of photochemical hole burning combined with Stark effect measurements was used to determine the values as a function of the burning frequency. For almost all systems an increase of DELTAmu(ind) from higher to lower optical frequencies was found. A plot of the [DELTAmu(ind)] values measured at the absorption band maximum vs the low-temperature values of the dielectric constant epsilon shows a clear correlation between the dipole moment difference and the low-temperature epsilon values over the whole investigated range which is accessible with commercially available polymers. In order to evaluate the data the dielectric constant epsilon of each sample was determined in a series of separate experiments as a function of frequency and temperature.