title: Molecular Packing Determines Charge Separation in a Liquid Crystalline Bisthiophene-Perylene Diimide Donor-Acceptor Material.
abstract: Combined electronic structure and quantum dynamical calculations are employed to investigate charge separation in a novel class of covalently bound bisthiophene-perylene diimide type donor-acceptor (DA) co-oligomer aggregates. In an earlier spectroscopic study of this DA system in a smectic liquid crystalline (LC) film, efficient and ultrafast (subpicosecond) initial charge separation was found to be followed by rapid recombination. By comparison, the same DA system in solution exhibits ultrafast resonant energy transfer followed by slower (picosecond scale) charge separation. The present first-principles study explains these contrasting observations, highlighting the role of an efficient intermolecular charge-transfer pathway that results from the molecular packing in the LC phase. Despite the efficiency of this primary charge-transfer step, long-range charge separation is impeded by a comparatively high Coulomb barrier in conjunction with small electron- and hole-transfer integrals. Quantum dynamical calculations are carried out for a fragment-based model Hamiltonian, parametrized by ab initio second-order Algebraic Diagrammatic Construction (ADC(2)) and Time-Dependent Density Functional Theory (TDDFT) electronic structure calculations. Simulations of coherent vibronic quantum dynamics for up to 156 electronic states and 48 modes are performed using the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method. Excellent agreement with experimentally determined charge separation time scales is obtained, and the spatially coherent nature of the dynamics is analyzed.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt , Max-von-Laue-Str. 7, 60438 Frankfurt, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Polkehn
authors.affiliation: WPI-Advanced Institute for Material Research, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tamura
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt , Max-von-Laue-Str. 7, 60438 Frankfurt, Germany.
authors.forename: Pierre
authors.initials: P
authors.lastname: Eisenbrandt
authors.affiliation: Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg - CNRS , 67034 Strasbourg Cedex 2, France.
authors.forename: Stefan
authors.initials: S
authors.lastname: Haacke
authors.affiliation: Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg - CNRS , 67034 Strasbourg Cedex 2, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Méry
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt , Max-von-Laue-Str. 7, 60438 Frankfurt, Germany.
authors.forename: Irene
authors.initials: I
authors.lastname: Burghardt