Although singlet fission research has a decades long history, its key intermediate, the triplet pair, has only recently been examined in detail. Prediction and initial verification of triplet-pair populations (e.g., the quintet <sup>5</sup>TT) by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy have been followed by deeper studies that have begun to elucidate intriguing properties.  We have expanded the repertoire of optically and electrically detected magnetic resonance techniques to characterize the evolution of triplet pairs from their birth in a spin-polarized configuration through dissociation or emission that reveals specific relaxation pathways. These pathways depend crucially on both the interchromophore juxtaposition as well as molecular axes orientation in a magnetic field.  Control over these parameters is accomplished through synthesis of targeted structures, primarily end-substituted heteroacenes, derived from theoretical predictions and manifested in precise crystal growth and alignment.  The connection between spin state and typical electronic state signatures, at times tenuous and challenging to make, can be revealed through correlation of decay timescales and the concurrent assignment of magnetic and optical spectra. The results point toward methods of producing pure <sup>5</sup>TT spin polarization and optical readout, as well as situations that lead to efficient TT dissociation and transport.  Understanding the various scenarios impacts the design of molecular downconversion, upconversion, and quantum information systems.

Molecular assemblies with controllable triplet-pair dynamics

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ACS Fall 2022

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