Femtosecond transient infrared and stimulated Raman spectroscopy shed light on the relaxation mechanisms of photo-excited peridinin

Year: 2015

Authors: Di Donato M., Ragnoni E., Lapini A., Foggi P., Hiller R.G., Righini R.

Autors Affiliation: LENS, European Lab Nonlinear Spect, Via N Carrara 1, I-50019 Sesto Fiorentino, Italy; Ist Nazl Ottica, I-50125 Florence, Italy; Univ Florence, Dipartimento Chim Ugo Schiff, I-50019 Sesto Fiorentino, Italy; Univ Perugia, Dipartimento Chim, I-06100 Perugia, Italy; Macquarie Univ, Dept Biol, Fac Sci & Engn, Sidney, BC 2109, Canada.

Abstract: By means of one- and two-dimensional transient infrared spectroscopy and femtosecond stimulated Raman spectroscopy, we investigated the excited state dynamics of peridinin, a carbonyl carotenoid occurring in natural light harvesting complexes. The presence of singly and doubly excited states, as well as of an intramolecular charge transfer (ICT) state, makes the behavior of carbonyl carotenoids in the excited state very complex. In this work, we investigated by time resolved spectroscopy the relaxation of photo-excited peridinin in solvents of different polarities and as a function of the excitation wavelength. Our experimental results show that a characteristic pattern of one- and two-dimensional infrared bands in the C=C stretching region allows monitoring the relaxation pathway. In polar solvents, moderate distortions of the molecular geometry cause a variation of the single/double carbon bond character, so that the partially ionic ICT state is largely stabilized by the solvent reorganization. After vertical photoexcitation at 400 nm of the S2 state, the off-equilibrium population moves to the S1 state with ca. 175 fs time constant; from there, in less than 5 ps, the non-Franck Condon ICT state is reached, and finally, the ground state is recovered in 70 ps. That the relevant excited state dynamics takes place far from the Franck Condon region is demonstrated by its noticeable dependence on the excitation wavelength.

Journal/Review: JOURNAL OF CHEMICAL PHYSICS

Volume: 142 (21)      Pages from: 212409-1  to: 212409-10

More Information: The authors gratefully acknowledge support from the Italian MIUR: Program No. PRIN-2010ERFKXL-004; program FIRB “Futuro in Ricerca 2010” Grant No. RBFR10Y5VW to M.D.D. and RBFR109ZHQ supporting A.L. The contribution from Project No. EFOR-CABIR L. 191/2009 art. 2 comma 44 is also gratefully acknowledged. This research has received funding also from LASERLAB-EUROPE (Grant Agreement No. 284464, EC’s 7th Framework Programme).
KeyWords: Charge transfer; Ground state; Infrared spectroscopy; Laser spectroscopy; Pigments; Raman spectroscopy; Solvents, Excited-state dynamics; Femtosecond stimulated raman spectroscopies; Femtosecond transient; Intramolecular charge transfers; Solvent reorganization; Stimulated Raman spectroscopy; Time-resolved spectroscopy; Two-dimensional transient, Excited states, carotenoid; peridinin, chemistry; infrared spectroscopy; light; quantum theory; Raman spectrometry; time, Carotenoids; Light; Quantum Theory; Spectroscopy, Fourier Transform Infrared; Spectrum Analysis, Raman; Time Factors
DOI: 10.1063/1.4915072

Citations: 18
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