Addition of a Carbonyl End Group Increases the Rate of Excited-State Decay in a Carotenoid via Conjugation Extension and Symmetry Breaking

Abstract

Steady-state absorption, transient absorption, and transient grating spectroscopies were employed to elucidate the role of a conjugated carbonyl group in the photophysics of carotenoids. Spheroidenone and spheroidene have similar molecular structures and differ only in an additional carbonyl group in spheroidenone. Comparison of the optical responses of these two molecules under similar experimental conditions was used to understand the role of this carbonyl group in the structure. It was found that the carbonyl group has two main effects: first, it dramatically increases the depopulation rate of the excited states of the molecule. The lifetimes of all the excited states of spheroidenone were found to be almost half of the ones for spheroidene. Second, the presence of the carbonyl group in the chain alters the decay mechanism to the symmetry-forbidden S1 state of the molecule, so that the higher vibrational levels of the S1 state are populated much more effectively. It was also revealed that for both molecules, the S2/S x → S1(hot) → S1 decay process is not purely sequential and follows a branched model.

Zero-length photo-crosslinking by organoiridium catalyst for intracellular interactome mapping

“…Ir-HTL and sIr-HTL were rationally designed to control triplet excited state lifetime by changing the distance between the ancillary ligand bipyridine (bpy) and the carbonyl group that acts as the excited state quencher (Supplementary Scheme 1). 38,39 As expected, time-correlated single photon counting in an aqueous solution demonstrated the triplet excited lifetime of Ir-HTL (704 ns) to be approximately two times longer than that of sIr-HTL (363 ns) because of the large distance (7.430 Å) between the carbonyl group and the bpy part of Ir-HTL (Fig. 1c).…”