The excited-state dynamics of 6,13-bis(triisopropylsilylethynyl)pentacene is investigated to determine the role of excimer and aggregate formation in singlet fission in high-concentration solutions. Photoluminescence spectra were measured by excitation with the evanescent wave in total internal reflection, in order to avoid reabsorption effects. The spectra over nearly two magnitudes of concentration were nearly identical, with no evidence for excimer emission. Time-correlated single-photon counting measurements confirm that the fluorescence lifetime shortens with concentration. The observed rate constant grows at high concentrations, and this effect is modeled in terms of the hard-sphere radial distribution function. NMR measurements confirm that aggregation takes place with a binding constant of between 0.14 and 0.43 M-1. Transient absorption measurements are consistent with a diffusive encounter mechanism for singlet fission, with hints of more rapid singlet fission in aggregates at the highest concentration measured. These data show that excimers do not play the role of an emissive intermediate in exothermic singlet fission in solution and that, while aggregation occurs at higher concentrations, the mechanism of singlet fission remains dominated by diffusive encounters.
|Number of pages||10|
|Journal||Journal of the American Chemical Society|
|State||Published - Sep 1 2021|
Bibliographical noteFunding Information:
This work was supported by the Australian Research Council (Centre of Excellence in Exciton Science CE170100026). This program has been supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). M.D. acknowledges CAAS grant no. CZ.02.1.01/0.0/0.0/16_019/0000778.
© 2021 American Chemical Society.
ASJC Scopus subject areas
- Chemistry (all)
- Colloid and Surface Chemistry