Mechanism of the Intramolecular Charge Transfer State Formation in all-trans-beta-Apo-8

Year: 2015

Authors: Ragnoni E., Di Donato M., Iagatti A., Lapini A., Righini R.

Autors Affiliation: LENS, I-50019 Florence, Italy; Ist Nazl Ottica, I-50125 Florence, Italy; Univ Firenze, Dipartimento Chim Ugo Schiff, I-50019 Florence, Italy.

Abstract: In this work we analyzed the infrared and visible transient absorption spectra of all-trans-beta-apo-8′-carotenal in several solvents, differing in both polarity and polarizability at different excitation wavelengths. We correlate the solvent dependence of the kinetics and the band shape changes in the infrared with that of the excited state absorption bands in the visible, and we show that the information obtained in the two spectral regions is complementary. All the collected time-resolved data can be interpreted in the frame of a recently proposed relaxation scheme, according to which the major contributor to the intramolecular charge transfer (ICT) state is the bright 1B(u)(+) state, which, in polar solvents, is dynamically stabilized through molecular distortions and solvent relaxation. A careful investigation of the solvent effects on the visible and infrared excited state bands demonstrates that both solvent polarity and polarizability have to be considered in order to rationalize the excited state relaxation of trans-8′-apo-beta-carotenal and clarify the role and the nature of the ICT state in this molecule. The experimental observations reported in this work can be interpreted by considering that at the FranckCondon geometry the wave functions of the S-1 and S-2 excited states have a mixed ionic/covalent character. The degree of mixing depends on solvent polarity, but it can be dynamically modified by the effect of polarizability. Finally, the effect of different excitation wavelengths on the kinetics and spectral dynamics can be interpreted in terms of photoselection of a subpopulation of partially distorted molecules.

Journal/Review: JOURNAL OF PHYSICAL CHEMISTRY B

Volume: 119 (2)      Pages from: 420  to: 432

More Information: The authors gratefully acknowledge support from the Italian MIUR: FIRB Futuro in Ricerca 2010 Grant RBFR10Y5VW to M.D.D. and RBFR109ZHQ supporting A.L.; PRIN, 2010ERFKXL_004 to R.R.; and the Regione Toscana, Project EFOR-CABIR L. 191/2009 art. 2 comma 44.
KeyWords: Internal-conversion Lifetime; Excited-state; Energy-transfer; Carotenoid Peridinin; Chlorophyll-protein; Ultrafast Dynamics; Singlet-state; Beta-carotene; Dependence; Light
DOI: 10.1021/jp5093288

Citations: 23
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