Michael addition of thiols to an electron deficient alkene functional
group in reagents (1)-(3) give rise to fluorescence quantum yield enha
ncements. In the absence of the thiol, photoinduced electron transfer
(PET) takes place from the fluorophore to the alkene moiety. Such elec
tron transfer is suppressed after the thiol reaction. (C) 1998 Elsevie
r Science Ltd. All rights reserved.