Nonconjugated Acyloxy Group Deactivates the Intramolecular Charge-Transfer State in the Carotenoid Fucoxanthin

• DOI: 10.1021/acs.jpcb.8b00743
• Publication Date: 2018-02-22T14:29:47Z
• Authors: Hristina Staleva-...; Valentyna Kuznetsova; Robert G. West; Gürkan Keşan; Babak Minofar; Marcel Fuciman; David Bína; Radek Litvín; Tomáš Polívka
• Keywords: TRANSIENT ABSORPTION-SPECTROSCOPY; Molecular Conformation; EXCITATION-ENERGY TRANSFER; NANNOCHLOROPSIS-OCEANICA; Molecular Dynamics Simulation; Xanthophylls; 01 natural sciences; 0104 chemical sciences; 3. Good health

We used ultrafast transient absorption spectroscopy to study excited-state dynamics of the keto-carotenoid fucoxanthin (Fx) and its two derivatives: 19′-butanoyloxyfucoxanthin (bFx) 19′-hexanoyloxyfucoxanthin (hFx). These derivatives occur in some light-harvesting systems photosynthetic microorganisms, their presence is typically related stress conditions. Even though hexanoyl (butanoyl) moiety not a part conjugated system hFx (bFx), spectra polar solvents exhibit more pronounced vibrational bands S2 state than for Fx. The effect nonconjugated acyloxy further observed spectra, which Fx characteristic features an intramolecular charge transfer (ICT) all solvents. For bFx hFx, however, much weaker ICT are detected methanol, spectral markers disappear completely polar, but aprotic acetonitrile. also alters lifetimes S1/ICT state. Fx, 60, 30, 20 ps n-hexane, acetonitrile, whereas these yield 40 ps, respectively. Testing other revealed that can be induced only protic (methanol, ethanol, ethylene glycol). Thus, represent rather rare example functional group significantly dynamics. By comparison with carotenoids, we show keto at tail, even it conjugation, affects electron distribution along backbone, resulting decrease character hFx.