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Fluorescence properties of some substituted acyclic azines

Journal of Luminescence
Publication Date
DOI: 10.1016/0022-2313(86)90037-2
  • Chemistry
  • Physics


Abstract Fluorescence spectra of some acyclic azines (2,3-diazabutadienes), namely ō-hydroxybenzaldizine (1), p̄-N, N-dimethyl-amino abenzaldazine (2) and 2-hydroxy-1-naphthaldazine (3) were determined in different solvents at ambient temperature and at 77 K. The results showed that radiative and nonradiative rates are essentially controlled by the structure of the molecules. The fluorescence of compounds (1)-(3) is enhanced sufficiently by affecting the nπ∗ nature of the S 1 state in different media. The fluorescence quantum yield Φ F increases significantly as the viscosity of the homogeneous medium increases and as the temperature is lowered to 77 K. However, Φ F reaches a limiting small value, indicating the existence of an important nonradiative decay channel involving formation of different rotamers and E-Z isomers. The results of quantum chemical calculations based on the Hückel MO method, show that optical excitation decreases bond alternation in the S 1 state, leading to increasing nonradiative decay. Furthermore, the results demonstrate that the photophysical properties of these compounds in an ionic micellar system (CTAB) differ from analogous properties in homogeneous solitions. Optical excitation of azines containing a hydroxyl group ((1) and (3)) gives rise to a large increase in their acidic properties suggesting that intramolecular proton transfer in these molecules can be switched on by optical excitation. We have focussed our interest on ō-hydroxybenzaldazine (1) since preliminary studies show that it may be a useful indicator for fluorimetric determination of the microproperties of the surrounding environment.

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