title: High intrachain order promotes triplet formation from recombination of long-lived polarons in poly(3-hexylthiophene) J-aggregate nanofibers.
abstract: Photoluminescence (PL) of single poly(3-hexylthiophene) (P3HT) J-aggregate nanofibers (NFs) exhibits strong quenching under intensity-modulated pulsed excitation. Initial PL intensities (I(0)) decay to steady-state levels (ISS) typically within ∼ 1-10 μs, and large quenching depths (I(0)/I(SS) >2) are observed for ∼ 70% of these NFs. Similar studies of polymorphic, H-aggregate type P3HT NFs show much smaller PL quenching depths (I(0)/I(SS) ≤ 1.2). P3HT chains in J-type NF π-stacks possess high intrachain order, which has been shown previously to promote the formation of long-lived, delocalized polarons. We propose that these species recombine nongeminately to triplets on time scales of >1 ns. The identity of triplets as the dominant PL quenchers was confirmed by subjecting NFs to oxygen, resulting in an instantaneous loss of triplet PL quenching (I(0)/I(SS) ∼ 1). The lower intrachain order in H-type NFs, similar to P3HT thin-film aggregates, localizes excitons and polarons, leading to efficient geminate recombination that suppresses triplet formation at longer time scales. Our results demonstrate the promise of self-assembly strategies to control intrachain ordering within multichromophoric polymeric aggregate assemblies to tune exciton coupling and interconversion processes between different spin states.
authors.affiliation: Department of Chemistry and Chemical Biology, University of New Mexico , MSC03 2060, Albuquerque, New Mexico 87131, United States.
authors.forename: Alan K
authors.initials: AK
authors.lastname: Thomas
authors.forename: José A
authors.initials: JA
authors.lastname: Garcia
authors.forename: Jordan
authors.initials: J
authors.lastname: Ulibarri-Sanchez
authors.forename: Jian
authors.initials: J
authors.lastname: Gao
authors.forename: John K
authors.initials: JK
authors.lastname: Grey
keywords: J-aggregate; P3HT nanofibers; intrachain order; polaron recombination; triplet quenching