Photoinduced chlorophyll charge transfer state identified in the light-harvesting complex II from a marine green alga Bryopsis corticulans

The light-harvesting complex II of Bryopsis corticulans (B-LHCII), a green alga, differs from that of spinach (S-LHCII) in chlorophyll (Chl) and carotenoid (Car) compositions. We investigated ultrafast excitation dynamics of B-LHCII with visible-to-near infrared time-resolved absorption spectroscopy. Absolute fluorescence quantum yield (Φ_FL) of LHCII and spectroelectrochemical (SEC) spectra of Chl a and b were measured to assist the spectral analysis. Red-light excitation at Chl Q_y-band, but not Car-band, induced transient features resembling the characteristic SEC spectra of Chl a^⋅+ and Chl b^⋅−, indicating ultrafast photogeneration of Chl-Chl charge transfer (CT) species; Φ_FL and ³Car^∗ declined whereas CT species increased upon prolonging excitation wavelength, showing positive correlation of ¹Chl^∗ deactivation with Chl-Chl CT formation. Moreover, ultrafast Chl b-to-Chl a and Car-to-Chl singlet excitation transfer were illustrated. The red-light induction of Chl-Chl CT species, as also observed for S-LHCII, is considered a general occurrence for LHCIIs in light-harvesting form.