title: Charge Localization after Ultrafast Photoexcitation of a Rigid Perylene Perylenediimide Dyad Visualized by Transient Stark Effect.
abstract: The intramolecular charge-transfer (CT) dynamics of a rigid and strongly conjugated perylenediimide-bridge-perylene dyad (PDIPe) has been investigated in dichloromethane using ultrafast transient electronic absorption spectroscopy and quantum chemical calculations. The strong electronic coupling between the dyad units gives rise to a CT band. Its photoexcitation forms a delocalized CT state with well-preserved ion bands despite the strong coupling. In the dyad, the electronic transition dipole moment of the electron donor perylene is aligned along the axis of the electric field vector with respect to the CT species. This alignment makes the donor sensitive to the Stark effect and thus charge density fluctuations in the CT state. Charge localization on the picosecond time scale manifests as a time-dependent Stark shift in the visible region. Quantum chemical calculations reveal a twist around the acetylene bridging unit to be the responsible mechanism generating a partial to an almost complete CT state. An estimate of the electric field strength in the CT state yields approximately 25 MV/cm, which increases to around 31 MV/cm during charge localization. Furthermore, the calculations illustrate the complexity of electronic structure in this strongly delocalized superchromophore and reflect the complications in the interpretation of transient absorption results when compared to steady-state approaches such as spectroelectrochemistry and model chromophore experiments such as photoinduced bimolecular charge transfer.
authors.affiliation: Department of Chemistry, Princeton University , Washington Road, Princeton, New Jersey 08540, United States.
authors.forename: Marius
authors.identifier: 0000-0001-8721-7613
authors.initials: M
authors.lastname: Koch
authors.affiliation: Department of Chemistry, North Carolina State University , Raleigh, North Carolina 27695-8204, United States.
authors.forename: Mykhaylo
authors.initials: M
authors.lastname: Myahkostupov
authors.affiliation: Department of Chemistry, Princeton University , Washington Road, Princeton, New Jersey 08540, United States.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Oblinsky
authors.affiliation: Department of Chemistry, Princeton University , Washington Road, Princeton, New Jersey 08540, United States.
authors.forename: Siwei
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Chemistry, North Carolina State University , Raleigh, North Carolina 27695-8204, United States.
authors.forename: Sofia
authors.initials: S
authors.lastname: Garakyaraghi
authors.affiliation: Department of Chemistry, North Carolina State University , Raleigh, North Carolina 27695-8204, United States.
authors.forename: Felix N
authors.identifier: 0000-0001-7546-8618
authors.initials: FN
authors.lastname: Castellano
authors.affiliation: Department of Chemistry, Princeton University , Washington Road, Princeton, New Jersey 08540, United States.
authors.forename: Gregory D
authors.identifier: 0000-0003-3336-7960
authors.initials: GD
authors.lastname: Scholes