STRUCTURE OF CAGE AMINES AS MODELS FOR TWISTED INTRAMOLECULAR CHARGE-TRANSFER STATES

Citation
G. Kohler et al., STRUCTURE OF CAGE AMINES AS MODELS FOR TWISTED INTRAMOLECULAR CHARGE-TRANSFER STATES, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 101(45), 1997, pp. 8518-8525
Citations number
26
Categorie Soggetti
Chemistry Physical
ISSN journal
10895639
Volume
101
Issue
45
Year of publication
1997
Pages
8518 - 8525
Database
ISI
SICI code
1089-5639(1997)101:45<8518:SOCAAM>2.0.ZU;2-L
Abstract
6-Cyanobenzquinuclidine (CBQ) is widely assumed to be a good model to study twisted internal charge transfer (TICT), a hypothesis proposed t o explain the appearance of solvent-induced dual fluorescence in 4-(N, N-dimethylamino)benzonitrile (DMABN) derivatives. This is due to the o rthogonal arrangement of the nitrogen lone pair and the aromatic pi or bitals in this cage amine and the exclusive appearance of long wavelen gth TICT fluorescence. Spectral and photophysical properties of CBQ ar e investigated by stationary and time-resolved fluorescence spectrosco py as a function of solvent polarity. The results are discussed in the context of conformational analysis studies performed for CBQ and benz quinuclidine by X-ray crystallography as well as by semiempirical calc ulations. It is shown that only one singlet excited state is emissive. Fluorescence spectra and intersystem crossing rates can be modeled as charge recombination processes, and excellent agreement between simul ated and measured data is found. Rehybridization of the amino group, w hich leads to a less pyramidal geometry, and torsional vibration about the bond linking the donor group and the benzonitrile moiety contribu te essentially to intramolecular charge separation and recombination p rocesses.