Abstract
The quadratic Stark effect was measured for chlorophyll monomer and dimer (Chl·ethanol) 2 in isotropic glassy solutions at low temperatures. The change in the permanent dipole moment, δμ, of chlorophyll monomer on excitation in the red absorption maximum was found to be (1.02±0.09) D for both mono- and disolvate. It forms an angle δ=20° with the electronic transition moment Q y . The electronic excitation of the dimer within its main absorption band at 703 nm is accompanied by the change in dipole moment Δμ=(5.17 ± 0.2) D, for which δ=23°. A remarkable contribution from polarizability change, Δα, to Stark spectra of both monomer and dimer was found within the Q y band. In the monomer, Δα is several times higher in the region of vibrational side bands, where it is related to the second electronic transition ( Q x ). The large increase in Δμ for the dimer as compared to the monomer is ascribed to charge-transfer contribution to the dimer excited state, due to significant overlap of electronic densities in the constituent monomers.
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