Effect of Isomer Geometry on the Steady-State Absorption Spectra and Femtosecond Time-Resolved Dynamics of Carotenoids

Abstract

Steady-state absorption and femtosecond time-resolved optical spectroscopic studies have been carried out on all-trans-beta-carotene, 15,15'-cis-beta-carotene, all-trans-spheroidene, and 13,14-locked-cis-spheroidene. We examine in detail the effect of isomer geometry on the spectroscopic properties and photophysics of the low-lying S(1) (2(1)A(g)(-)) and S(2) (1(1)B(u)(+)) excited states of these molecules. The experiments on 13,14-locked-cis-spheroidene, a molecule incapable of undergoing cis-to-trans isomerization, provide a unique opportunity to examine the role of isomer geometry in controlling excited-state deactivation of carotenoids. The kinetic results have been obtained using both single wavelength transient absorption measurements and global fitting procedures. The overall scheme for the deactivation of these molecules after S(0) --> S(2) photon absorption is decay of S(2) to a vibrationally hot S(1) state, followed by vibrational relaxation within S(1), and finally, S(1) --> S(0) internal conversion back to the ground state. Changes in isomer geometry are shown to lead to small but noticeable alterations in the spectroscopic and kinetic behavior of the molecules. The effects are interpreted in terms of minor alterations in excited-state energy and vibrational coupling upon isomerization that bring about changes in the spectroscopic and kinetic behavior of this biologically important class of pigments.

Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum

“…The profiles were normalized at their maxima; f the steady-state absorption spectrum (dotted line) and the TA spectrum taken in NIR range expressed in wavenumber scale and overlaid to obtain the best peak-valley agreement. The shift required to bring the spectra to coincidence defines the S 1 (2 1 A g -) state energy (11,350 cm -1 ) Photosynth Res (2011) 110:49-60 53 spectral shape and lifetime of *0.5 ps suggest that this EADS is associated with the ESA occurring from the vibrationally not equilibrated S 1 (2 1 A g -) state that was observed for a number of Cars with N = 11 and shorter in solvent environment as well as in a protein (Billsten et al 2003(Billsten et al , 2005Larsen et al 2003;Niedzwiedzki et al 2007Niedzwiedzki et al , 2009Papagiannakis et al 2006;Pendon et al 2005;Wohlleben et al 2003Wohlleben et al , 2004. The lifetime of the S 1 (2 1 A g -) state obtained from the fitting is 3.4 ps.…”

Ultrafast Time-Resolved Spectroscopy of Xanthophylls at Low Temperature

“…Such a transition is expected to be broader and red-shifted compared to transitions originating from a vibrationally relaxed S 1 (2 1 A g -) state. 11,[35][36][37] Of the models tested here, target model 2 ( Figure 5D) works best to account for the data from lutein and zeaxanthin. The global fits are shown in Figure 8 and the S 1 (2 1 A g -) and S* state lifetimes obtained from this model are summarized in Figure 9.…”

“…The vibrationally hot S 1 (2 1 A g -) relaxes within several hundreds of femtoseconds. 31, [35][36][37] For most xanthophylls, S* and S 1 (2 1 A g -) decay to the ground state in the range of 1-40 ps. 11 In the present work, ultrafast time-resolved spectroscopy was carried out at 77 K to examine the spectroscopic properties and dynamics of three major xanthophylls from green plants, violaxanthin, lutein, and zeaxanthin ( Figure 2).…”

Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

“…32,[35][36][37] Basically, they studied the reconstituted carotenoidless Rb. sphaeroides R-26.1 in which a locked-cis-SPO, which is supposed not to isomerize to all-trans configuration, was incorporated and showed that no difference in either spectroscopic properties or the photochemistry compared to the wild-type Rb.…”

“…Yet, studies by Pendon et al [35][36][37] in 2006 concluded against the hypothesis drawn by Koyama and co-workers. They reported ultrafast time-resolved spectroscopic studies of two pairs of stable geometric isomers of carotenoids including trans-SPO and 13,14-locked-cis-SPO, the latter of which is incapable of undergoing cis-to-trans isomerization at C13-C14…”