Photophysics of 7-mercapto-4-methylcoumarin and derivatives: complementary fluorescence behaviour to 7-hydroxycoumarins.

The photophysical behaviour of 7-mercapto-4-methylcoumarin (C-SH) and derivatives has been studied in different solvents. In contrast to 7-hydroxy-4-methylcoumarin, C-SH shows poor emission, but high fluorescence when the thiol is alkylated. The origin and character of the lowest singlet states are discussed, specifically proposing that the thione-like C=S resonance form plays a key role in excited state deactivation in C-SH. [ABSTRACT FROM AUTHOR]