The initial product of singlet fission, the spin-correlated triplet pair, has intriguing properties and potential for utility in different contexts, including photovoltaics/catalysis and quantum information.  We now have a large library of molecules that produce triplet pairs efficiently, and we have begun to explore the effects that molecular structure and interchromophore coupling have on the secondary processes of spin decorrelation and triplet pair or triplet exciton dissociation.  These are properties that have not been routinely studied, and as such we hope to gain fundamental information through systematic molecular design and spectroscopy.  I will describe several different classes of singlet fission chromophores: substituted anthradithophenes (ADT) and pentadithiophenes (PDT) and pentacene dioxalanes (PDO).  These classes exhibit variations from nearly isoergic to greatly exoergic singlet fission, and triplet pairs can be detected both optically and via electron paramagnetic resonance (EPR) spectroscopy. The coupling between molecules in the solid-state can be modulated by the choice of alkyl side chains, or through substitution with carboxylic acid or hydroxyl groups.  In the former case, steric effects offer an opportunity to systematically alter the packing mode to produce long-range π-stacking or isolated “dimer-like” interactions.  For substitution involving hydroxyls, hydrogen bonding primarily dictates the mode of molecular packing and can improve singlet fission rates into the sub-ps range for ADTs that previously showed much slower singlet fission dynamics in polycrystalline films.  We find that inducing long-range order in this fashion improves opportunities for forming independent and mobile triplets (important for photovoltaics) but can reduce spin correlation times.  Therefore, in PDTs and PDOs, we accept slower fission times (~100 ps) for truncated interactions that isolate triplet pairs that undergo spin evolution on the μs timescale.<br/>

Molecular control of triplet pair formation, spin correlation, and dissociation

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.