Excitonic splitting and Vibronic Coupling in 1,2-diphenoxyethane: Conformation-specific effects in the weak coupling limit

Published: May 30, 2013

Author(s)

buchanan Evan, Patrick Walsh, David F. Plusquellic, Timothy Zwier

Abstract

Vibrationally and rotationally resolved electronic spectra of 1,2-diphenoxyethane (C6H5-O-CH2-CH2-O-C6H5) are reported for the isolated molecule under jet-cooled conditions. The spectra demonstrate that the two excited surfaces are within a few cm-1 of one another over significant regions of the torsional potential energy surfaces that modulate the position and orientation of the two aromatic rings with respect to one another. Two-color resonant two-photon ionization (2C-R2PI) and laser-induced fluorescence (LIF) excitation spectra were recorded in the near-ultraviolet in the region of the close-lying S0-S1 and S0-S2 states (36,400 cm-1 – 36,750 cm-1). In previous work, double resonance spectroscopy in the ultraviolet and alkyl CH stretch regions of the infrared was used to identify and assign transitions to two conformational isomers differing primarily in the central C-C dihedral angle, a tgt conformation with C2 symmetry and a ttt conformation with C2h symmetry [Buchanan et al., accepted]. Comparison of 2C-R2PI spectra recorded in the m/z 214 (all 12C) and m/z 215 (one 13C) mass channels demonstrate the close proximity of the S1 and S2 excited states for both conformations, with an upper bound of 4 cm-1 between them. High resolution spectra of the origin band of the tgt conformer reveal it to consist of two transitions at 36422.91 cm-1 and 36423.93 cm-1, with transition dipole moments perpendicular to one another. These are assigned to the S0-S1 and S0-S2 origin transitions with excited states of A and B symmetry, respectively, and an excitonic splitting of only 1.02 cm-1. The excited state rotational constants and TDM directions prove that the electronic excitation is delocalized over the two rings. The ttt conformer has only one dipole-allowed electronic transition (Ag→Bu) giving rise to a pure b-type band at 36508.77 cm-1. Here, the asymmetry induced by a single 13C atom in one of the rings is sufficient to localize the electronic excitation in one or
Citation: Journal of Chemical Physics
Volume: 138
Pub Type: Journals

Keywords

Exciton coupling, vibronic coupling, weak coupling limit, bichromophores, UV-UV hole-burning, dispersed fluorescence, rotationally resolved, spectroscopy
Created May 30, 2013, Updated November 10, 2018