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Title: Unravelling vibrational and electronic coherences via two-dimensional electronic spectroscopy of zinc-porphyrins
Author: Valduga De Almeida Camargo, Franco
ISNI:       0000 0004 6351 1158
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2017
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Two-dimensional electronic spectroscopy (2D-ES) is a cutting edge experimental method to probe ultrafast phenomena such as energy transfer, chemical reactions, coherent wavepacket motion, etc. It is an extension of transient absorption methods which recovers the signal as a function of the excitation frequency, resolving signals that are overlapped in traditional techniques, and allowing simultaneous high spectral resolution in excitation frequency and high temporal resolution of the dynamics. 2D-ES studies of light-harvesting systems from photosynthetic organisms reported coherent wavepacket motion, attributed to electronic coherences between different exciton states. Vibrational and vibronic coherences can also be observed with 2D-ES, and it is thus important to study the specific signatures of each. In this thesis, we present an experimental setup that is well suited to recover coherent wavepacket motion and employ it to study vibrational coherences in a zinc-porphyrin monomer. A first experiment is analyzed with the traditional convention of using only the real part of the complex-valued 2D-ES signal, and interference between neighboring oscillatory features is revealed, explained and modeled. We also find that when the full complex-valued signal is analyzed, the most pronounced interference features disappear, and in this case an analysis based on double-sided Feynman diagrams suffices to describe all observations. We then report an experiment with a blue-shifted laser spectrum, which matches the molecular absorption in a way that is more commonly found in 2D-ES studies, and observe signatures that closely resemble the features expected for a purely electronic coherence, which we explain considering the laser spectrum for all three field-matter interactions. Finally, we demonstrate a 2D-ES experiment with a red-shifted spectrum which exclusively probes coherences in the ground state, complementing experiments with the blue-shifted spectrum. We argue that a combination of the two suffices for unambiguous interpretation of coherences in 2D-ES, lifting the need for an ultrabroadband laser.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available