Gas-phase energy of the S-2 <- S-0 transition and electrostatic properties of the S-2 state of carotenoid peridinin via a solvatochromic shift and orientation broadening of the absorption spectrum

作者：Pavlovich Vladimir S^*

来源：Photochemical and Photobiological Sciences, 2014, 13(10): 1444-1455.

DOI：10.1039/c4pp00124a

The solvent effect on the position and the shape of the absorption spectrum of peridinin for 12 protic and aprotic solvents as well as the temperature effect for methanol were studied using a solvatochromic theory based on the Onsager sphere cavity model. (Experimental data have been provided by T. Polivka and V. Sundstrom.) Solvatochromic calculations combined with estimations of orientation broadening of the absorption spectrum by convolution allowed the conclusion that the orientation (dipole-dipole), induction and dispersion solute-solvent interactions reasonably describes the position of the 0-0 frequency. The orientation interactions led to the blue solvatochromic shift, separating them from the induced and dispersion interactions, which produce a red shift. The FWHM of Gaussian of inhomogeneous broadening originated from the fluctuations of orientation interactions was demonstrated to be high (945 cm(-1)) even for such a nonpolar solvent as hexane. The value of vertical bar Delta mu vertical bar/cos phi of -18.7 D has been found (Delta mu = mu(2) - mu(g), phi is the angle between Delta mu and mu(g)). By assigning peridinin to the idealized C-2v point group, the large change of dipole moment vertical bar Delta mu vertical bar of 18.7 D under S-2 <- S-0 transition is obtained for peridinin in gas phase. Moreover, the S-2-excited state dipole moment mu(2) has the opposite orientation relative to that at the ground S-0 state mu(g). The determined gas-phase 0-0 energy of the S-2 <- S-0 transition, 22 910 cm(-1) (2.84 eV) is employed to calculate the polarizability change between the S-0 and S-2 states of 376 angstrom(3). The finding for the effective Onsager radius is of 9.4 angstrom. Obtained results for electrostatic properties of the S-2 state are compared with those known from Stark spectroscopy and quantum-mechanical calculations.

• 出版日期2014