Two temperature regimes of triplet transfer in the dissociation of the correlated triplet pair after singlet fission

Tia S. Lee, Yunhui L. Lin, Hwon Kim, Barry P. Rand, Gregory D. Scholes

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

The ability to undergo spin-allowed exciton multiplication makes singlet fission materials promising for photovoltaic applications. Here, we examine the separation of correlated triplet pairs, 1(T⋯T), in polycrystalline pentacene films via temperature-dependent transient absorption spectroscopy. Single wavelength analysis reveals a profound delay in 1(T⋯T) dynamics. Moreover, the dynamics of 1(T⋯T) exhibit temperature dependence, whereas other features show no discernable temperature dependence. Previous literatures have suggested that correlated triplet separation is mediated by a thermally activated hopping process. Surprisingly, we found that the time constants governing triplet pair separation display two distinct temperature-dependent regimes of triplet transport. The high temperature regime follows a thermally activated hopping mechanism. The experimentally derived reorganization energy and electronic coupling is verified by density matrix renormalization group quantum chemical calculations. In addition, we evaluated the low temperature regime and show that the trend can be modelled by a Miller-Abrahams-type model that incorporates the effects of energetic disorder. We conclude that the correlated triplet pair separation is mediated by thermally activated hopping or a disorder driven Miller-Abrahams-type mechanism at high and low temperature, respectively. We observe that crossover between two regimes occurs ∼226 K. We find the time constant for triplet-triplet energy transfer to be 1.8 ps at ambient temperature and 21 ps at 77 K.

Original languageEnglish (US)
Pages (from-to)465-473
Number of pages9
JournalCanadian Journal of Chemistry
Volume97
Issue number6
DOIs
StatePublished - Jan 1 2019

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry

Keywords

  • Disorder
  • Marcus theory
  • Miller-Abrahams transport
  • Pentacene
  • Spin entanglement
  • Thermal activation

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