Journal of Physical Chemistry A, Vol.115, No.11, 2110-2119, 2011
Femtosecond Transient Absorption Spectroscopic Study of a Carbonyl-Containing Carotenoid Analogue, 2-(all-trans-Retinylidene)-indan-1,3-dione
The photophysical properties of a carbonyl-containing carotenoid analogue in an s-cis configuration, relative to the conjugated pi system, 2-(all-trans-retinylidene)-indan-1,3-dione (C20Ind), were investigated by femtosecond time-resolved spectroscopy in various solvents. The lifetime of the optically forbidden S-1 state of C20Ind becomes long as solvent polarity increases. This trend is completely opposite to the situation of S1-ICT dynamics of carbonyl containing carotenoids, such as peridinin and fucoxanthin. Excitation energy dependence of the transient absorption measurements shows that the transient absorption spectra in nonpolar solvents were originated from two distinct transient species, while those in polar and protic solvents are due to a single transient species. By referring to the results of MNDO-PSDCI (modified neglect of differential overlap with partial single- and double configuration interaction) calculations, we conclude: (1) in polar and protic solvents, the S-1 state is generated following excitation up to the S-2 state; (2) in nonpolar solvents, however, both the S-1 and the (1)n pi* states are generated; and (3) C20Ind does not generate the S1-ICT state, despite the fact that it has two conjugated carbonyl groups.