Multiphonon relaxation slows singlet fission in crystalline hexacene

Erik Busby, Timothy C. Berkelbach, Bharat Kumar, Alexey Chernikov, Yu Zhong, Htay Hlaing, X. Y. Zhu, Tony F. Heinz, Mark S. Hybertsen, Matthew Y. Sfeir, David R. Reichman, Colin Nuckolls, Omer Yaffe

Research output: Contribution to journalArticlepeer-review

113 Scopus citations


Singlet fission, the conversion of a singlet excitation into two triplet excitations, is a viable route to improved solar-cell efficiency. Despite active efforts to understand the singlet fission mechanism, which would aid in the rational design of new materials, a comprehensive understanding of mechanistic principles is still lacking. Here, we present the first study of singlet fission in crystalline hexacene which, together with tetracene and pentacene, enables the elucidation of mechanistic trends. We characterize the static and transient optical absorption and combine our findings with a theoretical analysis of the relevant electronic couplings and rates. We find a singlet fission time scale of 530 fs, which is orders of magnitude faster than tetracene (10-100 ps) but significantly slower than pentacene (80-110 fs). We interpret this increased time scale as a multiphonon relaxation effect originating from a large exothermicity and present a microscopic theory that quantitatively reproduces the rates in the acene family.

Original languageEnglish
Pages (from-to)10654-10660
Number of pages7
JournalJournal of the American Chemical Society
Issue number30
StatePublished - 30 Jul 2014
Externally publishedYes


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