Photoselective ultrafast investigation of xanthorhodopsin and its carotenoid antenna salinixanthin.
Excited-state dynamics of xanthorhodopsin (XR) and of salinixanthin (SX) in ethanol were investigated by ultrafast pump-hyperspectral probe spectroscopy. Following excitation to the strongly allowed S(2) state of the SX chromophore, transient spectra were recorded photoselectively in the range 430-850 nm. Global kinetic analysis of these data shows the following. (1) Efficient energy transfer from S(2) of the SX in XR to its retinal moiety is verified here. The lifetime of S(2) in SX is, however, determined to be approximately 20 fs, much shorter than previously reported. (2) Branching ratios of excitation transfer from S(2) to S(1), to S*, and to retinal in XR are measured leading to species associated difference spectra (SADS) for all the states involved. Strong protein effects are detected on these branching probabilities. (3) S(1) and S* absorption bands in both systems exhibit anisotropy well below the expected r = 0.4, indicating an angle of approximately 25 degrees between the S(0) --> S(2) and S(1) --> S(n)/S* --> S(n) transition dipoles. The latter allows confident assignment of the debated S* absorption band to an excited state of SX, and not to "hot" S(0). In light of the extremely fast IC from S(2) to lower excited singlets, possible involvement of ballistic IC in SX, and of coherent energy transfer in XR, are discussed.
Zhu
Jingyi
J
Institute of Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University, Jerusalem 91904, Israel.
Gdor
Itay
I
Smolensky
Elena
E
Friedman
Noga
N
Sheves
Mordechai
M
Ruhman
Sanford
S
D001426:Bacterial Proteins / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D010777:Photochemistry; D011789:Quantum Theory; D025604:Rhodopsins, Microbial / Q000737:chemistry*; D013057:Spectrum Analysis
D001426:Bacterial Proteins; D006027:Glycosides; D025604:Rhodopsins, Microbial; C470489:salinixanthin; C519152:xanthorhodopsin, Salinibacter; D002338:Carotenoids