title: Electron transfer driven by proton fluctuations in a hydrogen-bonded donor-acceptor assembly.
abstract: The temperature-isotope dependence of proton-coupled electron transfer (PCET) for a noncovalent molecular dyad is reported. The system consists of an excited-state Zn(II) porphyrin that transfers an electron to a naphthalene diimide acceptor through an amidinium-carboxylate interface. Two different isotope effects are observed for variant temperature regimes. A reverse isotope effect (i.e., kH/kD < 1) is observed as T approaches 120 K (kH/kD = 0.9, 120 K), whereas a normal isotope effect (i.e., kH/kD > 1) is recovered as the temperature is increased (kH/kD = 1.2, 300 K). The transition between these limits is smooth, with a crossover temperature of T approximately 160 K. These observations are in accordance with charge-transfer dynamics that are susceptible to bath-induced fluctuations in the proton coordinate.
authors.affiliation: Department of Chemistry, 6-335, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
authors.forename: Justin M
authors.initials: JM
authors.lastname: Hodgkiss
authors.forename: Niels H
authors.initials: NH
authors.lastname: Damrauer
authors.forename: Steve
authors.initials: S
authors.lastname: Pressé
authors.forename: Joel
authors.initials: J
authors.lastname: Rosenthal
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Nocera
mesh_terms: D004579:Electron Transport; D006860:Hydrogen Bonding; D007094:Imides / Q000737:chemistry; D007554:Isotopes; D008665:Metalloporphyrins / Q000737:chemistry; D009281:Naphthalenes / Q000737:chemistry; D011522:Protons; D013696:Temperature
chemical_list: D007094:Imides; D007554:Isotopes; D008665:Metalloporphyrins; D009281:Naphthalenes; D011522:Protons; C017802:zinc hematoporphyrin