title: Solvent Polarity Tunes the Barrier Height for Twisted Intramolecular Charge Transfer in N-Pyrrolobenzonitrile (PBN).
abstract: 4-(1H-pyrrol-1-yl)benzonitrile (PBN) is a typical intramolecular donor-acceptor (D/A) molecule that shows dual fluorescence in weakly polar environments. In this work the underlying photochemical reaction mechanism is investigated theoretically by using high-level ab initio methods including the recently implemented third order algebraic diagrammatic construction of the polarization propagator (ADC(3)). Solvation effects have been considered by using different sophisticated continuum model approaches. Our results conclusively explain all available experimental findings including the effects of excitation wavelength, temperature and solvent polarity. After photoexcitation in gas phase to the bright 2A (S2, ππ*) state, PBN relaxes on the 2A state surface until a conical intersection with the energetically close-lying dark 1B (S1, LE) state is reached. After passing this conical intersection PBN further relaxes on the LE state surface toward a minimum from which emission can occur. In polar environments this picture changes. Then the polar 2B (S3, CT) state is stabilized and an energy barrier along the twisting coordinate vanishes. As a consequence population of the twisted 2B state minimum becomes the dominating decay channel and red-shifted fluorescence occurs.
authors.affiliation: Interdisciplinary Center for Scientific Computing, Ruprecht-Karls University , Im Neuenheimer Feld 368, 69120 Heidelberg, Germany.|Institute of Physical and Theoretical Chemistry, Goethe-University , Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.
authors.forename: Mercedes V
authors.initials: MV
authors.lastname: Bohnwagner
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe-University , Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.
authors.forename: Irene
authors.initials: I
authors.lastname: Burghardt
authors.affiliation: Interdisciplinary Center for Scientific Computing, Ruprecht-Karls University , Im Neuenheimer Feld 368, 69120 Heidelberg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Dreuw