Premium
WAVELENGTH EFFECTS ON THE PHOTOCYCLOREVERSION QUANTUM YIELD OF SOME PHOTOCHROMIC ENDOPEROXIDES
Author(s) -
Brauer H.D.,
Schmidt R.
Publication year - 1985
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1985.tb03458.x
Subject(s) - wavelength , quantum yield , chemistry , excited state , photochromism , singlet state , excitation , photon energy , photochemistry , excitation wavelength , quantum , yield (engineering) , photon , atomic physics , molecular physics , fluorescence , physics , optics , quantum mechanics , thermodynamics
— The photocycloreversion quantum yields Q of the endoperoxides of anthradichromene, benzodixanthene and dimethylhomoocoerdianthrone have been investigated in the 248 ≤γ≤ 405 nm wavelength range. Two types of wavelength dependencies can be distinguished phenomenologically. For the excitation of the S n (n ≥ 3) states of dimethylhomöocoerdianthrone endoperoxide γ‐independent Q‐values have been observed throughout 365 ≥γ≥ 265 nm. The endoperoxides of anthradichromene and benzodixanthene in contrast exhibit a quite different and unusual dependence of Q on γ. For both compounds Q first increases with photon energy until a fairly sharp maximum in Q is reached at 302 nm. With further increasing energy Q falls off and approaches a wavelength independent plateau between 280 and 248 nm. The S 1 ‐states of the endoperoxides investigated are inactive for photocycloreversion, which is generally found in endoperoxide photochemistry. The wavelength dependencies observed reveal that the photocycloreversion of endoperoxides deviates remarkably from the commonly accepted generalization that photochemical reactions in solution phase should only occur from the lowest excited singlet or triplet states.