Determining the static electronic and vibrational energy correlations via two-dimensional electronic-vibrational spectroscopy

Abstract

Changes in the electronic structure of pigments in protein environments and of polar molecules in solution inevitably induces a re-adaption of molecular nuclear structure.Both changes of electronic and vibrational energies can be probed with visible or infrared lasers, such as two-dimensional electronic or vibrational spectroscopies. The extent to which the two changes are correlated remains elusive. The recent demonstration of two-dimensional electronic-vibrational (2DEV) spectroscopy potentially enables a direct measurement of this correlation experimentally. However, it has hitherto been unclear how to characterize the correlation from the spectra. In this paper, we present a theoretical formalism to demonstrate the slope of the nodal line between the excited state absorption and ground state bleach peaks in the spectra as a characterization of the correlation between electronic and vibrational transition energies. We also show the dynamics of the nodal line slope is correlated to the vibrational spectral dynamics. Additionally, we demonstrate the fundamental 2DEV spectral line-shape of a monomer with newly developed response functions. a) Electronic mail: grfleming@lbl.gov 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 the isolated monomers, the decay of this slope is proportional to the correlation function for the bath-induced fluctuations in the energy of the vibrational transition, and there may be a long-time non-zero slope when there exists a correlation between the inhomogeneous distributions of the electronic and vibrational energy gaps. 30,31 Due to the electronic mixing in the dimer, the specific form of the center-line slope becomes more complicated, as it will contain contributions from multiple pathways and will depend on the electronic mixing angle and the correlation functions for the vibration on each monomer. The dynamics still reflect the correlation between the electronic and vibrational transitions, primarily induced via the fluctuations of the vibrational zero-point energies on the electronic excited state, but interference effects may complicate the precise dynamics.…”

“…Due to the very large difference in the frequencies of the electronic and vibrational coherences during the t 1 and t 3 periods, these pathways do not possess a significant rephasing power, and so, the information content of the rephasing and nonrephasing pathways is essentially equivalent. 30 Despite this, we maintain this language here to make a clear connection with degenerate spectroscopies. The response functions have the form…”

“…In this work, we extend the response functions recently developed for simulating the 2DEV spectra of a monomer, and successfully applied to the study of correlated electronic and vibrational spectral dynamics and disorder, 30,31 to the case of a molecular dimer. We then describe how these spectra can be used to directly measure the electronic site populations in a generic molecular aggregate without need for an accompanying model.…”

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

“…Using polarization anisotropy measurements, we demonstrate that bapo does not undergo any immediate trans−cis isomerization along the polyene backbone on the excited potential energy surface, counter to previous studies of bapo, 31,32 and other carotenoids. 39,40 We observe correlated and anticorrelated electronic and vibrational transition frequencies in 2DEV spectra, 41,42 for different vibrational modes on the excited states. From these different correlations, we are able to make far more rigorous assignments of the excited state vibrational frequencies in acetonitrile.…”