Semiempirical Characterization of Substituted Bis-pyrazolopyridines as
New Bulky Electron Donor-Acceptor Systems in Their Electronic Ground State
Andreas B. J.
Parusel1,2, Rudolf Schamschule1, Danuta Piorun3,
Karl Rechthaler1, Agnieszka Puchala3, Danuta Rasala3,
Krystyna Rotkiewicz3,4, Gottfried Köhler1
1Institute of Theoretical Chemistry and Radiationchemistry,
University of Vienna, Althanstr. 14, 1090 Vienna, Austria
2Institute of Physical Chemistry, University of Würzburg,
Marcusstr. 9-11, 97070 Würzburg, Germany
3Institute of Chemistry, Pedagogical University, Checinska 5, 25-020
Kielce, Poland
4Institute of Physical Chemistry, Polish Academy of Sciences,
Kasprzaka 44, 01-224 Warsaw, Poland
Contents
| H-DMPP |
DMA-DMPP |
 |
 |
|
|
| MeO-DMPP |
NO2-DMPP |
 |
 |
Geometries, conformational energies and activation barriers for rotations
about the single bonds connecting the various subunits of a new class of
bulky electron donor-acceptor systems derived from the bis-pyrazolopyridine
chromophore are characterized for several representatives by semiempirical
methods (AM1 and PM3). For the dimethylaminophenyl derivative DMA-DMPP (4-(4'-N,N-dimethylaminophenyl)-3,5-dimethyl-1,7-diphenyl-bis-pyrazolo-[3,4-b;4',3a-'e]pyridine)
dual fluorescence was observed in polar, protic solvents and was discussed in
the context with the TICT (twisted intramolecular charge transfer)
hypothesis, first formulated to explain dual fluorescence of 4-(N,N-dimethylamino)-benzonitrile
(DMABN). Besides the parent H-DMPP molecule, derivatives substituted with
different donor or acceptor groups were compared in respect to their optimum
ground state geometries.
Keywords:
Semiempirical calculations, Bis-pyrazolopyridine, Twisted
intramolecular charge transfer, Dual fluorescence, Donor-acceptor systems,
Transition states