Unravelling vibrational and electronic coherences via two-dimensional electronic spectroscopy of zinc-porphyrins

Valduga De Almeida Camargo, Franco (2017) Unravelling vibrational and electronic coherences via two-dimensional electronic spectroscopy of zinc-porphyrins. Doctoral thesis, University of East Anglia.

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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
su�ffices 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 su�ffices for unambiguous interpretation of coherences in 2D-ES, lifting the need for
an ultrabroadband laser.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Users 4971 not found.
Date Deposited: 01 Jun 2017 11:13
Last Modified: 01 Jun 2017 11:13
URI: https://ueaeprints.uea.ac.uk/id/eprint/63645

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