Gas-phase energy of the S2←S0 transition and electrostatic properties of the S2 state of carotenoid peridinin via a solvatochromic shift and orientation broadening of the absorption spectrum

Abstract

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. Sundström.) 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 |Δμ|/cos φ of -18.7 D has been found (Δμ = μ2 - μg, φ is the angle between Δμ and μg). By assigning peridinin to the idealized C2v point group, the large change of dipole moment |Δμ| of 18.7 D under S2←S0 transition is obtained for peridinin in gas phase. Moreover, the S2-excited state dipole moment μ2 has the opposite orientation relative to that at the ground S0 state μg. The determined gas-phase 0-0 energy of the S2←S0 transition, 22 910 cm(-1) (2.84 eV) is employed to calculate the polarizability change between the S0 and S2 states of 376 Å(3). The finding for the effective Onsager radius is of 9.4 Å. Obtained results for electrostatic properties of the S2 state are compared with those known from Stark spectroscopy and quantum-mechanical calculations.

Theoretical FRET Efficiency of an Antenna Material Containing Natural Dyes and Zeolite L

“…The angle formed by the μ gs of ZEA and the c -axis of the ZLCH is 70.7°, while the same angle for the μ es is 4.5° (Table ). Applying the aforementioned relationship, the magnitude of the ETDM of ZEA may still increase up to 14.801 D. In the last reference study, the theoretical relationship agreed well with Stark spectroscopic experiments …”

“…Applying the aforementioned relationship, the magnitude of the ETDM of ZEA may still increase up to 14.801 D. In the last reference study, the theoretical relationship agreed well with Stark spectroscopic experiments. 93 …”

Pigment organisation in the membrane-intrinsic major light-harvesting complex of Amphidinium carterae: Structural characterisation of the peridinins and chlorophylls a and c2 by resonance Raman spectroscopy and from sequence analysis

“…The ν 1 values of Per, at 77 K, in both non-polar (~1526.4 cm) and polar protic and aprotic solvents (~1528 cm −1 ) point to a conjugation length over eight dBs, extending over the polyene backbone and into the lactone carbonyl, and confirm that Per adopts a linear all-trans conformation at 77 K. The relatively low intensity of the ν 3 and ν 4 progressions and the almost absent HOOP bands off the polyene backbone, indicate that Per is planar and undistorted in the ground state at 77 K, consistent with the transition dipole moment of Per being nearly parallel to the polyene backbone [14,43]. The ν 1 value of Per is low for an eight dB conjugated system [24], and even lower than that of Fx [30], whose conjugation length also extends over eight dBs, likely because the lactone moiety in Per reduces the force constant of the total C_C/C_O coupled system below that of the C_O group conjugated into the polyene backbone of Fx.…”

Peridinin Torsional Distortion and Bond-Length Alternation Introduce Intramolecular Charge-Transfer and Correlated Triplet Pair Intermediate Excited States

“…Schulten and Karplus pointed out the existence of a dark S 1 state in butadiene, and other dark intermediate states were identified by Tavan and Schulten in the context of longer polyenes . Since these theoretical studies, the notion of dark intermediates has been much debated in the experimental and theoretical literatureespecially in the context of radiationless relaxation. , These debates take on heightened complexity for carbonyl carotenoids, such as peridinin, that may exhibit photophysics indicative of intramolecular charge transfer (ICT). − Peridinin ICT is believed to stem from electron-rich allene and electron-withdrawing lactone functionalization. The ICT character in peridinin has been invoked to explain its unique photophysics distinguished by emission solvatochromism and Stark spectroscopy .…”