Multidimensional Electronic Spectroscopy of Photochemical Reactions

Abstract

Coherent multidimensional electronic spectroscopy can be employed to unravel various channels in molecular chemical reactions. This approach is thus not limited to analysis of energy transfer or charge transfer (i.e. processes from photophysics), but can also be employed in situations where the investigated system undergoes permanent structural changes (i.e. in photochemistry). Photochemical model reactions are discussed by using the example of merocyanine/spiropyran-based molecular switches, which show a rich variety of reaction channels, in particular ring opening and ring closing, cis-trans isomerization, coherent vibrational wave-packet motion, radical ion formation, and population relaxation. Using pump-probe, pump-repump-probe, coherent two-dimensional and three-dimensional, triggered-exchange 2D, and quantum-control spectroscopy, we gain intuitive pictures on which product emerges from which reactant and which reactive molecular modes are associated.

Optimizing sparse sampling for 2D electronic spectroscopy

“…15 Most of the experimental realizations rely on the non-collinear box geometry and heterodyned detection of a coherent optical signal. Another option that has been developed is action-based 2D spectroscopy using a train of four (often collinear) laser pulses and a phase-modulation, 10,16 or phase-cycling scheme.…”

“…Furthermore, it may also be useful to perform an additional Fourier transform with respect to the population time T and generate a quasi-3D spectrum in order to distinguish the origin of coherences 26,27 or different channels in molecular reactions. 15,28 Fully coherent fifth-order 3D spectroscopy methods have also been demonstrated. [29][30][31][32] Thus, in action-based multidimensional spectroscopy, the time-domain parameter space can become very large, reaching easily hundreds of thousands of different configurations.…”

Quantum Control of Population Transfer and Vibrational States via Chirped Pulses in Four Level Density Matrix Equations

“…A central aspect in both approaches, CC and QCS, is the control of population transfer between the ground and excited states, as well as the generation of vibrational coherence in both potential surfaces. By controlling the population transfer or by suppressing specific molecular vibrational coherences, a photochemical reaction channel can be selectively chosen [27,29,32,[37][38][39][40][41][42][43][44][45][46][47][48][49], or a certain mode in a multidimensional time-resolved signal can be suppressed [37,[50][51][52][53][54][55].…”

Resolving Vibrational from Electronic Coherences in Two-Dimensional Electronic Spectroscopy: The Role of the Laser Spectrum

“…The extra dimension, given by the excitation frequency axis, yields 2D spectra where discrimination of specific features (otherwise overlapped in 1D methods) is now possible [1]. Consequently, 2D-ES has provided new insights into topics as diverse as quantum phenomena in biology [2][3][4], energy transfer [5,6], singlet fission [7], nanomaterials [8,9], reaction dynamics [10][11][12], and many body effects in coupled quantum wells [13][14][15]. However, although 2D-ES greatly facilitates the discrimination of physical phenomena affecting electronic transitions such as line-broadening mechanisms, vibrational and electronic couplings, ambiguities remain in detailed analysis, especially for molecular systems where both vibrational and electronic couplings may play a role.…”