title: Vibronic line shapes of PTCDA oligomers in helium nanodroplets.
abstract: Oligomers of the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride, C(24)H(8)O(6) (PTCDA) are studied by means of helium nanodroplet isolation spectroscopy. In contrast to the monomer absorption spectrum, which exhibits clearly separated, very sharp absorption lines, it is found that the oligomer spectrum consists of three main peaks having an apparent width orders of magnitude larger than the width of the monomer lines. Using a simple theoretical model for the oligomer, in which a Frenkel exciton couples to internal vibrational modes of the monomers, these experimental findings are nicely reproduced. The three peaks present in the oligomer spectrum can already be obtained taking only one effective vibrational mode of the PTCDA molecule into account. The inclusion of more vibrational modes leads to quasicontinuous spectra, resembling the broad oligomer spectra.
authors.affiliation: Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, D-01187 Dresden, Germany. roden@mpipks-dresden.mpg.de
authors.forename: Jan
authors.initials: J
authors.lastname: Roden
authors.forename: Alexander
authors.initials: A
authors.lastname: Eisfeld
authors.forename: Matthieu
authors.initials: M
authors.lastname: Dvořák
authors.forename: Oliver
authors.initials: O
authors.lastname: Bünermann
authors.forename: Frank
authors.initials: F
authors.lastname: Stienkemeier