title: Exciton delocalization drives rapid singlet fission in nanoparticles of acene derivatives.
abstract: We compare the singlet fission dynamics of five pentacene derivatives precipitated to form nanoparticles. Two nanoparticle types were distinguished by differences in their solid-state order and kinetics of triplet formation. Nanoparticles that comprise primarily weakly coupled chromophores lack the bulk structural order of the single crystal and exhibit nonexponential triplet formation kinetics (Type I), while nanoparticles that comprise primarily more strongly coupled chromophores exhibit order resembling that of the bulk crystal and triplet formation kinetics associated with the intrinsic singlet fission rates (Type II). In the highly ordered nanoparticles, singlet fission occurs most rapidly. We relate the molecular packing arrangement derived from the crystal structure of the pentacene derivatives to their singlet fission dynamics and find that slip stacking leads to rapid, subpicosecond singlet fission. We present evidence that exciton delocalization, coincident with an increased relative admixture of charge-transfer configurations in the description of the exciton wave function, facilitates rapid triplet pair formation in the case of single-step singlet fission. We extend the study to include two hexacene derivatives and find that these conclusions are generally applicable. This work highlights acene derivatives as versatile singlet fission chromophores and shows how chemical functionalization affects both solid-state order and exciton interactions and how these attributes in turn affect the rate of singlet fission.
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Ryan D
authors.initials: RD
authors.lastname: Pensack
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Tilley
authors.affiliation: ‡Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Parkin
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Tia S
authors.initials: TS
authors.lastname: Lee
authors.affiliation: ‡Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States.
authors.forename: Marcia M
authors.initials: MM
authors.lastname: Payne
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Dong
authors.initials: D
authors.lastname: Gao
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Ashlee A
authors.initials: AA
authors.lastname: Jahnke
authors.affiliation: §Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Oblinsky
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Peng-Fei
authors.initials: PF
authors.lastname: Li
authors.affiliation: ‡Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States.
authors.forename: John E
authors.initials: JE
authors.lastname: Anthony
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Dwight S
authors.initials: DS
authors.lastname: Seferos
authors.affiliation: †Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada.|§Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Scholes