Exploring Excited State Charge Transfer and Vibrational Coherences with Ultrafast Spectroscopy

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The interaction between light and matter is a basic concept for the understanding of natural
processes fundamental for all life on our planet. In the last three decades, femtochemistry
has been developed to investigate the first steps of photoinduced reactions such as
photochemistry or ultrafast DNA photoprotection mechanisms. In this thesis, the
application of ultrafast techniques to three systems and the study of charge transfer
mechanisms and vibrational coherences generated by ultrashort pulses is presented.
A combined experiment of transient absorption and time-resolved infrared spectroscopies
is used to investigate a model DNA composed of guanine and thymine, d(GpT). This study
univocally demonstrates the formation of delocalised Franck-Condon excited state upon
photoirradiation, which mediate a charge transfer mechanism with d(G+
pT-
) exciplex
formation.
In Chapter 5, the implementation of a state-of-the-art phase stable spectrometer which
allows the acquisition of both broadband transient absorption and two-dimensional
electronic spectroscopy data is presented. The setup is characterised by boxcar geometry
and used to investigate the solvation dynamics of Oxazine 4 in different solvents. Data
analysis reveals the generation of vibrational wave packets in both the ground and excited
state of the dye in solution. Franck-Condon active modes are retrieved from the purely
vibrational coherent spectra and assigned. From the comparison of frequency-frequency
maps of Oxazine 4 in methanol and ionic liquid, a much slower recovery of the central line
slope is observed when the ionic liquid surrounds the rigid dye.
The solvation dynamics of zinc chlorin e6 in solution and inside a protein scaffold is also
studied with broadband transient absorption spectroscopy. The ultrafast analysis reveals
vibrational wave packets generated in the ground and excited state and a less efficient
ability to “solvate” of the protein compared to conventional solvents.
Date of Award29 Sep 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorTom Oliver (Supervisor)

Cite this

Exploring Excited State Charge Transfer and Vibrational Coherences with Ultrafast Spectroscopy
Duchi, M. (Author). 29 Sep 2020

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)