Theoretical description of solvent effects on fluorescence spectra of bulky charge transfer compound DMA-DMPP
✍ Scribed by Parusel, Andreas B. J.; Schamschule, Rudolf; K�hler, Gottfried
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 796 KB
- Volume
- 19
- Category
- Article
- ISSN
- 0192-8651
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✦ Synopsis
Several theoretical models are compared to reproduce the Ž . spectroscopic fluorescence shift of 4-4Ј-N, N-dimethylaminophenyl -3,5w x Ž . dimethyl-1,7-diphenyl-bis-pyrazolo-3,4-b;4Ј,3Јe -pyridine DMA-DMPP in different solvents. DMA-DMPP is used as a model compound because it shows a large shift in emission energy for solvents of various polarities and dual fluorescence in polar protic solvents. Although the simple Onsager model is not able to reproduce the experimental results, the self-consistent reaction field Ž
. SCRF model with extension to excited states based on the AM1 Hamiltonian yields excellent agreement. According to the latter model, the red-shifted emission band can be related to a highly polar charge transfer state without Ž . geometrical rearrangements, whereas the normal short wavelength emission is attributed to emission from an excited state with increased conjugation in a flattened geometry. A supramolecular approach with six molecules of water surrounding the solute can explain satisfactorily the two distinct fluorescence bands. In protic solvents, the emitting CT state shows additional stabilization of the locally excited state with a planar conformation.