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2 Polish Journal of Chemistry

2 2008

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The Excited State Relaxation Path of N,N-Diethyl-5-cyanopyridine and N,N-Diethylbenzaldehyde

Dobkowski J., Sazanovich I.

Polish Journal of Chemistry

2008

Vol. 82, nr 4

831-845

The molecules which possess, as electron donors, dialkylamino groups linked by a single bond with the acceptor subunits undergo fast excited state intramolecular charge transfer (ICT), emitting dual fluorescence in polar solvents. The short and the long-wave length fluorescence bands are traditionally assigned as Fb and Fa, respectively. The nature of the excited state from which the Fa emission originates, as well as the mechanism of energy degradation have been the subject of many controversies. As the objects of this study, 2-(N,N-di ethyl)-5-cyanopyridine (PEC) and p-N,N-diethylaminoacetophenone (DEABA) were selected. For these molecules different sequence of the two low-lying pi pi* La and Lb states was postulated, which can help to verify the excited state mechanisms of the charge separation. The experimental results obtained by stationary and time-resolved spectroscopy show that the anomalous Fa emission originates from the ICT state generated by the mutual twist of the donor and acceptor group (TICT model).

Hydrogen Bonding and Protonation Effects on Excited-state Electron Transfer in meta and para-Dialkylaminopyridines

Szydłowska I., Nowacki J., Zielińska A., Herbich J.

Polish Journal of Chemistry

2008

Vol. 82, nr 4

847-864

Synthetic, spectral and photophysical investigations were performed for a series of dialkylaminopyridines (DAAPs) representing electron donor-acceptor systems. 4-Dimethyl aminopyridine and its analogues, substituted by an electron donor at the para position of the acceptor ring, show solvent-dependent dual luminescence from the substrate (primary excited state) and the product (TICT state) of the photoinduced electron transfer process. The investigations in mixed solvents (n-hex ane + 1-butanol) allow us to prove that dual luminescence is observed for 1:1 complexes of 4-DAAPs with the alcohol molecule hydrogen-bonded to the pyridine nitrogen atom. Contrary to 4-DAAPs, the electronic structure and geometry of the fluorescent CT state of 3-diisopropyl amino-pyridine are solvent-dependent (this 1CT state does not correspond to a full separation of charges). The spectroscopic and photophysical properties of the protonated forms of DAAPs are also presented. It is note worthy that the monocations of 4-diisopropyl-aminopyridine exhibit TICT fluorescence.