Molecular excitons in a copper azadipyrrin complex.
- Resource Type
- Article
- Authors
- McLean, T. M.; Telfer, S. G.; Elliott, A. B. S.; Gordon, K. C.; Lein, M.; Waterland, M. R.
- Source
- Dalton Transactions: An International Journal of Inorganic Chemistry. 2014, Vol. 43 Issue 47, p17746-17753. 8p.
- Subject
- *COPPER compounds spectra
*EXCITON theory
*METAL complexes
*ELECTRONIC structure
*LIGANDS
- Language
- ISSN
- 1477-9226
Exciton coupling is investigated in a copper azadipyrrin complex, Cu(L-aza)2. Exciton coupling in Cu(Laza) 2 assuming a single p-p* state on the L-aza ligand fails to account for the electronic structure of Cu(L-aza)2, which displays two almost equal intensity transitions at 15600 cm-1 and 17690 cm-1. TD-UB3LYP/6-31G(d) calculations suggest multiple p-p* transitions for the L-aza ligands and simple vector addition of the transition dipoles predicts two nearly orthogonal co-planar excitonic transitions that correctly reproduce the absorption band profile. Empirical modelling of absolute resonance Raman intensities using wavepacket dynamics confirms Cu(L-aza)2 has two equal intensity orthogonal exciton transitions. The phenyl substituents at the α- and γ-positions of the pyrrole rings play a central role in determining the orientation of the transition dipoles. Consequently the p-p* transitions for the L-aza ligands are oriented towards the substituent groups and are not in the plane of the pyrrole rings. Mode displacements in the Franck-Condon (FC) region obtained from the wavepacket model suggest that pyrrole ring and phenyl modes control the exciton FC dynamics. Our results suggest that Cu(L-aza)2 is an ideal model for theoretical, computational and experimental investigations of molecular excitons in molecular systems. [ABSTRACT FROM AUTHOR]