Download optical transitions and excitonic coupling in a covalently linked

OPTICAL TRANSITIONS AND EXCITONIC COUPLING IN A
COVALENTLY LINKED SPIROINDOLONE BICHROMOPHORE
Alexander Wohlert, Jörg Tatchen*
Institute of Theoretical and Computational Chemistry, Heinrich Heine University,
Universitätsstraße 1, D-40225 Düsseldorf, Germany.
email: [email protected]
We present a quantum chemical study of the electronic excitation spectrum of a novel luminescent
bichromophoric dye [1] which is made up of a diphenylbutadiene and an indolone unit which is carrying a
dansyl moiety. Experimentally, a broad fluorescence band with a maximum at 511 nm has been observed
[1] which could in principle result as emission from either one of the chromophores or even from both (dual
fluorescence). In order to unravel the mechanisms behind the luminescence, we calculate absorption and
emission spectra employing both time-dependent density functional theory and a combined density
functional theory/multi-reference configuration interaction approach [2]. Minima on the excited state
potential energy surfaces which correspond to a good approximation to local excitations are identified. The
role of charge-transfer and double excitations is discussed. Strictly local excitations are generated by
means of the fragment molecular orbital approach [3]. Different possibilities for obtaining the excitonic
couplings within the covalently linked system from the strictly local excitations will be explored.
[1] D. M. D’Souza, A. Kiel, D.-P. Herten, F. Rominger, T. J. J. Müller, Chem. Eur. J. 14, 529 (2008). J. Schönhaber,
Dissertation. Düsseldorf (2010).
[2] S. Grimme, M. Waletzke, J. Chem. Phys. 111, 5654 (1999).
[3] K. Kitaura, E. Ikeo, T. Asada, T. Nakano, M. Uebayasi, Chem. Phys. Lett. 313, 701 (1999). M. Chiba, D. G.
Fedorov, K. Kitaura, J. Chem. Phys. 127, 104108 (2007).