We employ a combination of linear spectroscopy, electrochemistry, and transient absorption spectroscopy to characterize the interplay between electron transfer and singlet fission dynamics in polyacene-based dyes attached to nanostructured TiO2. For triisopropyl silylethynyl (TIPS)-pentacene, we find that the singlet fission time constant increases to 6.5 ps on a nanostructured TiO2 surface relative to a thin film time constant of 150 fs, and that triplets do not dissociate after they are formed. In contrast, TIPS-tetracene singlets quickly dissociate in 2 ps at the molecule/TiO2 interface, and this dissociation outcompetes the relatively slow singlet fission process. The addition of an alumina layer slows down electron injection, allowing the formation of triplets from singlet fission in 40 ps. However, the triplets do not inject electrons, which is likely due to a lack of sufficient driving force for triplet dissociation. These results point to the critical balance required between efficient singlet fission and appropriate energetics for interfacial charge transfer.
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N. A. P., D. H. A., S. C. and J. C. J. acknowledge the Solar Photochemistry Program supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences, and Geosciences under Contract No. DE-AC36-08GO28308 with NREL for support of transient absorption and steady-state spectroscopy, ALD, and electrochemistry. D. B. G. and J. E. A. thank the National Science Foundation (DMREF-1627428) for support of acene synthesis.
Electronic supplementary information (ESI) available: Steady-state UV-VIS and PL, solution transient absorption, X-ray diffraction, decay associated spectra, and TIPS Tc COOH/Al2O3/TiO2 film kinetics. See DOI: 10.1039/c7sc04688j
Pace, Natalie A.; Arias, Dylan H.; Granger, Devin B.; Christensen, Steven; Anthony, John E.; and Johnson, Justin C., "Dynamics of Singlet Fission and Electron Injection in Self-Assembled Acene Monolayers on Titanium Dioxide" (2018). Chemistry Faculty Publications. 127.