MULTISITE PHOSPHORESCENCE OF ALPHA,BETA-ENONES - 3N-PI-STAR-3-PI-PI-STAR LEVEL INVERSION IN 6-BETA, 19-EPOXYCHOLEST-4-EN-3-ONE BY SOLVATION AND AGGREGATION

被引:4
作者
BLOK, PML [1 ]
DEKKERS, HPJM [1 ]
机构
[1] LEIDEN STATE UNIV,GORLAEUS LABS,POB 9502,2300 RA LEIDEN,NETHERLANDS
关键词
D O I
10.1111/j.1751-1097.1991.tb03652.x
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Millisecond time-resolved emission spectroscopy was used to probe the phosphorescence kinetics of the alpha-beta-enone 6-beta,19-epoxycholest-4-en-3-one (1) as a function of concentration in several paraffinic and hydroxylic glasses at 77 K. Only in methylcyclohexane/methylcyclopentane glass at low concentration (10(-4) M) does the phosphorescence decay exponentially. It is interpreted as emission from the 3n-pi* state. Upon increasing the concentration a second emission grows which is characterized by a longer lifetime, a decreased fine structure and a hypsochromically shifted S0 --> 1n-pi* excitation spectrum. This phosphorescence is ascribed to 3-pi-pi* emission of aggregates of 1. In hydroxylic glasses the phosphorescence decay is multiexponential, even at 10(-4) M concentration; from emission band shapes and lifetimes it follows that both 3n-pi* and 3-pi-pi* type emissions are present, the latter increasing with the alcohol concentration in the solvent. The two types of phosphorescence have different excitation spectra: that of the structureless and long-lived 3-pi-pi* emission is shifted to the blue in the S0 --> 1n-pi* region and to the red in the S0 --> 1-pi-pi* region. This emission is ascribed to complexes of 1 with the alcoholic solvent. The results of time-resolved measurements of the circular polarization of the luminescence are consistent with the assignments given above and indicate that in the H-bonded and possibly also in the free species 3-pi-pi* and 3n-pi* states are intermixed to a considerable extent.
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页码:421 / 429
页数:9
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