posted on 2023-12-28, 20:13authored byJonathan
R. Palmer, Malik L. Williams, Ryan M. Young, Kathryn R. Peinkofer, Brian T. Phelan, Matthew D. Krzyaniak, Michael R. Wasielewski
The photogeneration of multiple unpaired electron spins
within
molecules is a promising route to applications in quantum information
science because they can be initialized into well-defined, multilevel
quantum states (S > 1/2) and reproducibly fabricated
by chemical synthesis. However, coherent manipulation of these spin
states is difficult to realize in typical molecular systems due to
the lack of selective addressability and short coherence times of
the spin transitions. Here, these challenges are addressed by using
donor–acceptor single cocrystals composed of pyrene and naphthalene
dianhydride to host spatially oriented triplet excitons, which exhibit
promising photogenerated qutrit properties. Time-resolved electron
paramagnetic resonance (TREPR) spectroscopy demonstrates that spatially
orienting triplet excitons in a single crystal platform imparts narrow,
well-resolved, tunable resonances in the triplet EPR spectrum, allowing
selective addressability of the spin sublevel transitions. Pulse-EPR
spectroscopy reveals that at temperatures above 30 K, spin decoherence
of these triplet excitons is driven by exciton diffusion. However,
coherence is limited by electronic spin dipolar coupling below 30
K, where T2 varies nonlinearly with the
optical excitation density due to exciton annihilation. Overall, an
optimized coherence time of T2 = 7.1 μs
at 20 K is achieved. These results provide important insights into
designing solid-state molecular excitonic materials with improved
spin qutrit properties.