Study of the vibronic mixing in chlorophylls with multidimensional spectroscopy

Sammanfattning: Chlorophylls comprise one of the most important families of molecules for the photosynthetic process. Chlorophyll-like molecules have been classically interpreted under the Gouterman model, being thought to feature two independent transitions, Qy(S1) and Qx(S2). Recent studies on the matter provided a new interpretation, assuming these states to feature strong vibronic coupling and to be inseparably mixed. Experimental study of vibronic mixing can be done with non-linear spectroscopy techniques that can create and record superpositions of states, the so-called "coherences". These coherences, when excited via vibronically coupled transitions, represent a direct observation of vibronic mixing phenomena. Polarization-controlled two-dimensional electronic spectroscopy is performed on chlorophyll a at cryogenic (77 K) temperature, followed by a complex analysis to the oscillatory signals, unveiling vibronic coupling in the most common member of the chlorophyll family.