title: Crossover from single-step tunneling to multistep hopping for molecular triplet energy transfer.
abstract: Triplet energy transfer (TT), a key process in molecular and organic electronics, generally occurs by either strongly distance-dependent single-step tunneling or weakly distance-dependent multistep hopping. We have synthesized a series of pi-stacked molecules consisting of a benzophenone donor, one to three fluorene bridges, and a naphthalene acceptor, and studied the rate of TT from benzophenone to naphthalene across the fluorene bridge using femtosecond transient absorption spectroscopy. We show that the dominant TT mechanism switches from tunneling to wire-like hopping between bridge lengths 1 and 2. The crossover observed for TT can be determined by direct observation of the bridge-occupied state.
authors.affiliation: Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Josh
authors.initials: J
authors.lastname: Vura-Weis
authors.forename: Sameh H
authors.initials: SH
authors.lastname: Abdelwahed
authors.forename: Ruchi
authors.initials: R
authors.lastname: Shukla
authors.forename: Rajendra
authors.initials: R
authors.lastname: Rathore
authors.forename: Mark A
authors.initials: MA
authors.lastname: Ratner
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wasielewski