Following Coupled Electronic-Nuclear Motion through Conical Intersections in the Ultrafast Relaxation of β-Apo-8′-carotenal

Abstract

Ultrafast transient electronic absorption, one- and two- dimensional electronic-vibrational spectroscopies were used to study the nonradiative relaxation dynamics of β-apo-8'-carotenal (bapo), a model aldehyde containing carotenoid, in cyclohexane and acetonitrile solutions. 2D electronic-vibrational (2DEV) spectroscopy allows for a direct correlation between the intrinsically coupled electronic and vibrational degrees of freedom, which are thought to play an important role in driving relaxation of bapo from the bright S2 and lower-lying dark S1 state. Line shapes of features in the 2DEV spectra allow us to make more definitive assignments of excited state vibrations of bapo in acetonitrile. Anisotropy studies definitively demonstrate that the excited state dynamics of bapo do not involve a trans-cis isomerization, counter to prior hypotheses. For specific vibrational modes, the electronic and vibrational line shapes remain correlated beyond the decay of the S2 excited state, indicating that the transfer of molecules to the S1 state is impulsive and involves a conical intersection in the vertical Franck-Condon region.

The Study of Reactive Intermediates in Condensed Phases

“…This transient 2DIR (t-2DIR) approach remains experimentally challenging, with signals that are significantly weaker than normal TVA measurements, and only a few examples have been reported to date. 87 The hybrid 2DEV method examines the coupling between electronic and vibrational (i.e., nuclear) motions in molecules, 88,89 and has the potential to examine reactive intermediates corresponding to photoexcited states. between the pump and probe IR pulses, the spectrum is dominated by features on the diagonal corresponding to the degenerate (e') stretching modes of the equatorial CO ligands (at 1999 cm -1 ) and the a2" stretching mode of the axial ligands (at 2022 cm -1 ).…”

Vibronic mixing enables ultrafast energy flow in light-harvesting complex II

“…The commonly employed technique of twodimensional electronic spectroscopy (2DES) often lacks the spectral resolution to untangle the complex, congested spectra of relevant systems-making it challenging to discern whether or not an oscillatory feature is electronic, vibrational, or vibronic in nature 21 . Although recent work has successfully unveiled the presence of vibronic coupling in natural and artificial lightharvesting systems [28][29][30][31][32][33][34] , the newly developed technique of twodimensional electronic-vibrational (2DEV) spectroscopy 7,[35][36][37][38][39][40][41][42][43][44] , by focusing on vibrational transitions in the final light-matter interaction, has the potential to provide significantly improved experimental input into the interplay of electronic and nuclear dynamics in ultrafast energy (and charge) transfer. Several aspects of 2DEV spectroscopy are significant in this regard.…”

A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

“…For example, 2DEV spectra of the C==C backbone stretch mode in DTTCI are dominated by the electronic ground state feature, 31 whereas in 8 ′ -apo-β-caroten-8 ′ -al, the spectrum is dominated by electronic excited state features. 53,54 Additionally, it is often easier to assign vibrations on the ground electronic state, due to the computational expense of ab initio excited state frequency analysis.…”