The full dynamics of energy relaxation in large organic molecules: from photo-excitation to solvent heating

Abstract

In some molecular systems, such as nucleobases, polyenes or sunscreens, substantial amounts of photo-excitation energy are dissipated on a sub-picosecond time scale. Where does this energy go or among which degrees of freedom it is being distributed at such early times?

Excited‐State Evolution of Keto‐Carotenoids after Excess Energy Excitation in the UV Region

“…Regardless the exact S* origin, these results showed that there indeed is a correlation between energy dissipation (vibrational cooling, internal vibrational redistribution) and the S* signal in carotenoids [29] . Thus, studies of excited state relaxation pathways upon excess energy excitation represent a promising approach to reveal further details about energy dissipation/redistribution in carotenoids.…”

“…The short excited state lifetimes of carotenoids imply fast and efficient dissipation of absorbed energy both to molecular vibrations, generating hot states, and eventually to the environment [29] . This is especially important for long (N>12) carotenoids, for which the energy absorbed via the S 0 ‐S 2 transition (∼20000 cm −1 ) is non‐radiatively dissipated within ∼1 ps [17,30,31] .…”

“…These authors showed that for β ‐carotene the S* signal originates entirely from the S 1 state associated with a specific ground state conformation. However, for carotenoids with larger N, which have clearly separated S 1 and S* lifetimes, the experimental data could not be reproduced unless a contribution from the hot ground state to the S* signal is considered [29,37,41] . Thus, the S* band in a particular carotenoid will consist of signals originating from both excited and ground states, to which various processes, such as line shape distortions due to local heating, absorption from vibrational excited state or even inhomogeneous ground state, may contribute [29] …”

A Protein Environment-Modulated Energy Dissipation Channel in LHCII Antenna Complex

“…The current view of the origin of the S∗ signal in solution points toward contributions from both a vibrational shoulder of S 1 and “hot” ground-state effects ( Balevičius et al., 2016 ; Ehlers et al., 2018 ). The hot ground-state contribution to the S∗ signal is probably a combination of long-lasting vibrational excitation and slow heat dissipation to the environment ( Balevičius et al., 2019 ). Even though a “hot” ground state is the inevitable product of rapid excitation quenching by S 1 , it is clearly not the origin of the 515 nm band.…”

Revealing a full quantum ladder by nonlinear spectroscopy

“…Several spectroscopic methods, including infrared and ultraviolet absorption, Raman, jet-cooled laser-induced fluorescence, have been utilized to map out the whole series of vibrational quantum states of molecules in their ground and excited electronic states [43][44][45]. These multiple quanta properties are very important for numerous molecular processes such as chemical reactions [46,47], isomerization or inversion [48][49][50][51][52], as well as energy transfer during inelastic collisions proceeding along vibrational pathways that are governed by vibrational potential energy surfaces [53,54]. Development of spectroscopic approaches to reveal the whole vibrational (or electronic) potential surface is thus highly demanded and simple nonlinear spectroscopy probes may aid in this direction.…”