Transient Absorption Study of Peridinin and Peridinin−Chlorophyll <i>a</i>−Protein after Two-Photon Excitation

Abstract

Two-photon excited pump−probe spectroscopy was carried out on the peridinin−chlorophyll a−protein complex (PCP) and on the peridinin molecule in methanol solution. Our data are consistent with earlier two-photon fluorescence excitation spectra1,2 and lead to the conclusion that, for peridinin in methanol solution, a separate two-photon-allowed transition exists just to the red of the strongly allowed S0 − S2(Bu+) band. In the PCP complex, two-photon excitation at 1150 nm can also be interpreted as preparing a new state. In both cases, the new state is most likely the S1(Ag-) state. It is not yet possible to conclude experimentally whether peridinin possesses a single low lying state with solvent dependent properties or two distinct states, the Ag- and the charge transfer states.