Multiple Quintets via Singlet Fission in Ordered Films at Room Temperature

TL;DR

This study demonstrates room-temperature formation of distinct quintet excitons in ordered pentacene-p-terphenyl films, emphasizing the role of molecular geometry in singlet fission efficiency for photovoltaic applications.

Contribution

It provides experimental evidence linking intermolecular geometry to quintet exciton formation, advancing understanding of structure-function relationships in singlet fission materials.

Findings

Distinct quintet excitons observed at room temperature

Angular dependence links excitons to specific molecular pairs

Highlights importance of controlling molecular geometry

Abstract

The growing interest in harnessing singlet fission for photovoltaic applications stems from the possibility of generating two excitons from a single photon. Quantum efficiencies above unity have been reported, yet the correlation between singlet fission and intermolecular geometry is poorly understood. To address this, we investigated ordered solid solutions of pentacene in p-terphenyl grown by organic molecular beam deposition. Two classes of dimers are expected from the crystal structure - parallel and herringbone - with intrinsically distinctive electronic coupling. Using electron paramagnetic resonance spectroscopy, we provide compelling evidence for the formation of distinct quintet excitons at room temperature. These are assigned to specific pentacene pairs according to their angular dependence. This work highlights the importance of controlling the intermolecular geometry and the need to develop adequate theoretical models to account for the relationship between structure and electronic interactions in strongly-coupled, high-spin molecular systems.