Kavli Affiliate: David T. Limmer
| First 5 Authors: Thomas P. Fay, David T. Limmer, , ,
| Summary:
Triplet excited state generation plays a pivotal role in photosensitizers,
however the reliance on transition metals and heavy atoms can limit the utility
of these systems. In this study, we demonstrate that an interplay of competing
quantum effects control the high triplet quantum yield in a prototypical boron
dipyrromethene-anthracene (BD-An) donor-acceptor dyad photosensitizer, which is
only captured by an accurate treatment of both inner and outer sphere
reorganization energies. Our ab initio-derived model provides excellent
agreement with experimentally measured spectra, triplet yields and excited
state kinetic data, including the triplet lifetime. We find that rapid triplet
state formation occurs primarily via high-energy triplet states through both
spin-orbit coupled charge transfer and El-Sayed’s rule breaking intersystem
crossing, rather than direct spin-orbit coupled charge transfer to the lowest
lying triplet state. Our calculations also reveal that competing effects of
nuclear tunneling, electronic state recrossing, and electronic polarizability
dictate the rate of non-productive ground state recombination. This study sheds
light on the quantum effects driving efficient triplet formation in the BD-An
system, and offers a promising simulation methodology for diverse photochemical
systems.
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