Numerous photophysical processes in both natural and artificial systems are dictated by the interaction between chromophores. For example, in photosynthesis, light is absorbed by an antenna complex composed of an array of chlorophyll chromophores that collectively transfer the energy to the reaction center where interactions between a series of redox sites leads to long-distance, long-lived electron transfer. Similarly, one factor dictating the efficiency in organic photovoltaic devices is the formation of separated charges which is highly dependent on the propensity of the material for forming charges that are delocalized over multiple chromophores. As such, a key question that is actively being researched by many groups is the role that coherence and interchromophore interactions play in the efficiency of these processes and to what degree they can be engineered into functional devices. To that end, the work presented here has two foci: (i) investigating the nature and dynamics of excited states in covalent dimers and (ii) employing covalent dimers as acceptors in photodriven electron transfer reactions. To address these topics, time-resolved vibrational and electronic spectroscopy are used to characterize the excited states and monitor the excited-state processes that occur following photoexcitation. Specifically, femtosecond stimulated Raman spectroscopy was utilized to study the structure and character of the excimer and correlated pair states. Results indicated that the vibrational structure provides an indication of the degree to which these mixed-character states are comprised the constituent electronic states, specifically the charge resonance and local exciton states for excimers and the local exciton, triplet exciton, and charge resonance states for the correlated pair. Transitioning to electron transfer reactions, electronic absorption spectroscopy was employed to monitor the rate of charge separation and recombination in donor-acceptor supramolecular architectures comprised of a dimer of acceptors. Results suggest that when the system-bath interactions are reduced, from both structural and thermal vantages, coherent interactions between the two sites in the acceptor dimer can lead to non-statistical scaling in the rate of electron transfer with the number of acceptors. This work highlights the need to consider both interchromophore and system-bath interactions when attempting to engineer coherent effects.

Creator

• Phelan, Brian Thomas

DOI

• https://doi.org/10.21985/n2-z8t2-ng29

Subject

• Physical chemistry

Language

• en

Alternate Identifier

• etdadmin_upload_633520
• http://dissertations.umi.com/northwestern:14489

Keyword

• Time-resolved spectroscopy
• Electron transfer
• Photophysics
• Quantum coherence
• Singlet fission
• Excimer

Date created

• 2018-01-01

Resource type

• Dissertation

Rights statement

• In Copyright