UV/vis-absorption and fluorescence spectroscopic study of some new 4-hydroxy-7-methoxycoumarin derivatives. Part 2. Effect of esterification by a diphenylphosphatidic acid

4-Hydroxycoumarin (1a) and a polysubstituted derivative (2a) were treated with chlorodiphenylphosphate to give the corresponding diphenylphosphatidylcoumarins, lc and 2c, respectively. For the sake of comparison, the hydroxycoumarins 1a and 2a were also esterified by acetic acid to yield 1b and 2b, respectively. These compounds were studied by UV/vis-absorption and fluorescence spectroscopy. In the 4-hydroxycou-marin series, fluorescence was quenched after substitution by the phosphate group, which is reminiscent of the behaviour of 4-methyl-umbelliferyl-phosphate (4-MUP). In contrast, for the polysubstituted compounds, the fluorescence quantum yield of the phosphate derivative was much higher than that of the corresponding hydroxycoumarin. For both series, the phosphate-bearing derivatives were markedly less emissive than the acetyl ester analogues (1b and 2b).