title: The degree of charge transfer in ground and charge-separated states revealed by ultrafast visible pump/mid-IR probe spectroscopy.
abstract: We demonstrate a new femtosecond visible pump/mid-IR probe spectroscopic approach to assess directly the ground- and excited-state degrees of charge transfer (CT) in donor-spacer-acceptor (D-Sp-A) structures. Two classes of (porphinato)zinc(II) (PZn)-based D-Sp-A compounds with either quinonyl (Q) or N-(N'-octyl)pyromellitic diimide (PI) electron acceptors were interrogated. Carbonyl antisymmetric stretching mode frequency domain transient-IR spectra of these species were recorded and analyzed for the Q/PI moieties. These data show that the acceptor mode frequency shift, DeltanuA, determined by this method provides a more accurate measure of the degree of CT in ground and charge-separated states relative to other techniques which rely on the ground-state frequency shift alone. This approach enables determination of new experimental benchmarks to test the power of complimentary computational methods and provides a means to probe the degree of CT in transitions that either overlap strongly with other bands or possess low oscillator strength.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, 19104-6323, USA.
authors.forename: Igor V
authors.initials: IV
authors.lastname: Rubtsov
authors.forename: Youn K
authors.initials: YK
authors.lastname: Kang
authors.forename: Naomi P
authors.initials: NP
authors.lastname: Redmore
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Allen
authors.forename: Jieru
authors.initials: J
authors.lastname: Zheng
authors.forename: David N
authors.initials: DN
authors.lastname: Beratan
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Therien