PHOTOPHYSICAL PROPERTIES OF SOME HIGHLY FLUORESCENT DERIVATIVES OF VITAMIN-B-1 - SOLVENT EFFECT

The influence of the solvent on the photophysical properties of some h ighly fluorescent vitamin B-1 derivatives (the products of the reactio n of N-methylated vitamin B-1 with cytidine (I), adenosine (II) and 2- amino-4-methylpyridine (III)) was studied using absorption and fluores cence techniques (both steady state and time resolved). For II and III , the photophysical properties do not change significantly in various solvents. For I, a large decrease in the fluorescence quantum yield an d lifetime of the singlet state is observed on going from acetonitrile to alcohol. These large changes in the photophysical parameters of I occur in spite of the small changes in the absorption spectrum and the shape of the fluorescence spectrum. No evidence for a specific solute -solvent interaction, i.e. a complex of I with alcohols, is found in p ure (including deuterated solvents) or mixed solvents. The measured va lues of the intersystem crossing (ISC) quantum yield of I in acetonitr ile and methanol (in the region of 10(-2)) indicate that the ISC proce ss is not responsible for the observed solvent effect. Possible explan ations for the influence of the solvent on the photophysical propertie s of I in its first excited singlet state are discussed.