Fluorescence Characteristics of 3-Aminoisocarbostyril Derivatives (1)

Fluorescent characteristics of 3-aminoisocarbostyril derivatives were examined from the viewpoint of the substituent effect in comparison with 3-aminoisocarbostyril (Ia) as a parent compound. 3-Amino-(Ib-f, IIIa, b) and 3-substituted aminoisocarbostyril derivatives (IIa-e) gave larger fluorescence quantum yields in ethanol than that of Ia. The fluorescence quantum yield of Ia was increased by the replacement of methoxy and alkylamino groups at C7 and C3, respectively. It was suggested that the basicity of C3-amino group may play an important part for the enhancement of their fluorescence. On the other hand, the fluorescence quantum yields of 2-amino-3-hydrazinoisocarbostyril derivatives (IVa-f) were negligibly small. On the basis of the consideration of the fluorescence and phosphorescence spectral data, it was assumed that the decrease in the fluorescence quantum yields of IVa-f was attributed to the intersystem crossing from 1(ππ*) to 3(ππ*).