STARK-EFFECT ON SPECTRAL HOLES OF CHLOROPHYLL A AT 2 K

We studied the electric field effect on spectral holes burned in the S ,cSo absorption band of in poly(vinyl butyral) film doped chlorophyll (Chl) a at a temperature of T = 2.0 K. With the laser light beam colli nearly applied, the external electric field produced a symmetric broad ening of the holes which showed a linear dependence on the field stren gth. This effect was ascribed to the matrix-induced dipole moment diff erence (Delta mu(ind)) between the S-1 and S-0 states of Chl a. The re latively small value of Delta mu(ind) (0.217 D), is in accord with the change of the molecular polarizability upon electronic excitation. Th e low-temperature permanent dipole moment difference of Chl a was esti mated to be less than 0.1 D.