Intramolecular charge-transfer state of carotenoids siphonaxanthin and siphonein: function of non-conjugated acyl-oxy group

Electronic and Vibrational Properties of Allene Carotenoids

“…Thus, the allene group per se is not fully conjugated, as concluded earlier, from the absence of typical allene frequencies in the resonance Raman spectra of fucoxanthin. 18 We needed to perform careful analysis separately for the absorption peak positions and Raman assignments of the selected carotenoids (Cars), which required different DFT methodologies as well.…”

“…It is worth noting that the π-orbitals of the two CC bonds of the allene group are necessarily orthogonal to each other so that only one can be involved in the conjugated chain. Thus, the allene group per se is not fully conjugated, as concluded earlier, from the absence of typical allene frequencies in the resonance Raman spectra of fucoxanthin . We needed to perform careful analysis separately for the absorption peak positions and Raman assignments of the selected carotenoids (Cars), which required different DFT methodologies as well.…”

“…The electronic properties of Fx can be tuned by its environment to a greater extent than usually observed for carotenoids, its absorption being shifted to wavelengths as high as 550 nm in photosynthetic light-harvesting proteins . This red absorption shift was proposed to arise from an intramolecular charge transfer (ICT) character of the second excited state, generated by the electron-rich keto group. − Polívka’s group showed that this ICT can be deactivated by the presence of a nonconjugated, oxygen-rich acyloxy group at the opposite end of the conjugated chain to the keto carbonyl (see the bFx structure in Figure ), while when positioned on the same end as the keto, this group rather enhances the ICT state . The significant electron-withdrawing character of the acyloxy group, although nonconjugated, is thus able to counteract the effect of the conjugated keto group.…”

“… 13 − 17 Polívka’s group showed that this ICT can be deactivated by the presence of a nonconjugated, oxygen-rich acyloxy group at the opposite end of the conjugated chain to the keto carbonyl 12 (see the bFx structure in Figure 1 ), while when positioned on the same end as the keto, this group rather enhances the ICT state. 18 The significant electron-withdrawing character of the acyloxy group, although nonconjugated, is thus able to counteract the effect of the conjugated keto group.…”

Discovery of a novel siphonaxanthin biosynthetic precursor in Codium fragile that accumulates only by exposure to blue‐green light

“…The absorption spectrum of dS in the organic solvent exhibited less development towards longer wavelengths than those of S and Sn (Fig. S2Da), indicating a weaker ICT effect [49]. Based on these considerations, the interconversion from S to dS may decrease the ICT‐dependent energy transfer efficiency, resulting in a reduction in energy transfer to the reaction centre.…”