GORNER, H and FISCHER, C and DAUB, J (1995) PHOTOREACTION OF DIHYDROAZULENES INTO VINYLHEPTAFULVENES - PHOTOCHROMISM OF NITROPHENYL-SUBSTITUTED DERIVATIVES. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 85 (3). pp. 217-224. ISSN 1010-6030,
Full text not available from this repository.Abstract
The photophysical and photochemical properties of five nitro-substituted dihydroazulene (DHA) derivatives, 1,8a-dihydro-2-(R-phenyl)-1,1-azulenedicarbonitrile, where R is 2-NO2, 3-NO2, 4-NO2, 2,4-(NO2), and 3,5-(NO2)(2) (2-, 3-, 4-, 2,4- and 3,5-D respectively) were studied in solvents of different polarity at various temperatures. Irradiation of the DHAs in fluid solution leads to the corresponding vinylheptafulvenes (VHFs) which show neither emission nor photoreactivity. At room temperature, the quantum yield of the DHA-->VHF photoreaction depends on the substitution and solvent; Phi(D-->V) is substantial for 4-D (approximately 0.5) and very small (0.02-0.005) for 2- and 2,4-D, while for 3- and 3,5-D Phi(D-->V) decreases with increasing solvent polarity. Fluorescence from the excited singlet state of 4-, 3- and 3,5-D is observed at low temperatures; the quantum yield is largest for 4-D (Phi(i) greater than or equal to 0.5 at -196 degrees C) and much smaller (0.002 or less) for 2- and 2,4-D. At room temperature, Phi(f) is very low throughout. The absorption spectrum of the triplet state is observed at room temperature for those cases, e.g. 2- and 2,4-D, for which Phi(D-->V) is small, and enhanced triplet-triplet absorption is found in all cases using sensitizers, e.g. xanthone in acetonitrile. The DHA triplet energy was estimated from energy transfer measurements to be about 220 kJ mol(-1). The triplet state is not involved in the photochromism of the nitro-substituted DHAs. The effects of nitro groups at different positions in the phenyl ring on the photophysical and photochemical behaviour are discussed.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | TRANS->CIS PHOTOISOMERIZATION; REVERSIBLE PHOTOCHEMISTRY; CHARGE SEPARATION; EXCITED-STATES; SYSTEM; PERSPECTIVES; FLUORESCENCE; SOLVENT; TICT; DIHYDROAZULENES; VINYLHEPTAFULVENES; PHOTOCHROMISM |
| Depositing User: | Dr. Gernot Deinzer |
| Last Modified: | 19 Oct 2022 08:38 |
| URI: | https://pred.uni-regensburg.de/id/eprint/52788 |
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