Dissertations, Theses, and Capstone Projects
Date of Degree
9-2026
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy
Program
Chemistry
Advisor
Matthew Y. Sfeir
Committee Members
Chen Wang
Claudia Avalos
Ronald Koder
Luis M. Campos
Subject Categories
Physical Chemistry
Keywords
Singlet Fission, Charge Accumulation, Transient Absorption Spectroelectrochemistry, Bridge Resonance, Quantum Interference
Abstract
Singlet fission is a photophysical process in which one singlet exciton generates two triplet excitons through a correlated triplet-pair intermediate. Historically, this process has been studied primarily as a strategy to harvest independent triplets for solar energy conversion. This research moves beyond that traditional view by treating the bound triplet-pair state as a unique multiexcitonic entity capable of driving multiexciton-mediated photochemistry. Specifically, this work demonstrates that the correlated multiexciton state generated by intramolecular singlet fission can drive one-electron and two-electron transfer processes before dephasing into independent triplets. To achieve this goal, we used a molecular design approach to integrate electron donors, electron acceptors into singlet fission chromophores. Ultrafast transient absorption spectroscopy, electrochemical methods, spectroelectrochemistry, transient absorption spectroelectrochemistry, and computational modeling were used to understand the excited-state dynamics and determine how molecular structure, redox state, and solvent polarity control the competition between singlet fission, charge transfer, and triplet-pair dephasing. Donor-integrated tetracene dimers demonstrated that the triplet-pair state can mediate efficient one-electron transfer into charge-separated states, with solvent polarity controlling the kinetic balance between intramolecular singlet fission and electron transfer. Acceptorintegrated systems further revealed that redox-active bridges (organic and transition-metalcoordination complexes) can strongly modulate singlet fission dynamics through quantum interference, bridge resonance, and interligand charge-transfer states. Finally, fully integrated donor-acceptor architectures provided first experimental evidence for multiexciton-mediated two-electron transfer. Computational modeling based on continuum solvation and electron-transfer theory rationalized the solvent-dependent kinetic regimes observed experimentally and identified the energetic and kinetic windows required for multiexciton-mediated charge separation. However, the simultaneous two-electron transfer process was not fully reproduced by conventional classical or semi-quantum Marcus-type models, suggesting that this process represents a distinct kinetic regime requiring further theoretical development. Together, these results establish a molecular framework for multiexciton-mediated photochemistry in singlet fission chromophores. By moving beyond the traditional harvesting of independent triplets, this research demonstrates that the correlated triplet-pair state can be directly used to drive new photochemical transformations, establishing the based for future develop in multielectron transfer, photocatalysis, and reaction
Recommended Citation
Salcido Santacruz, Bernardo Arturo, "A Molecular Framework for Multiexciton Photochemistry: One- and Two-Electron Transfer in Singlet Fission Chromophores" (2026). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/6809
