DESIGN OF MULTIPLEX DYES

Fluorescent dyes which are almost identical in their absorption and em ission spectral characteristics but differ in fluorescence lifetime (' 'Multiplex Dyes'') have been developed for analytical applications. Fi rst investigations to design such dyes were carried out with rhodamine s. In order to influence the excited state lifetime without changing t he spectral characteristics we studied rhodamines modified with non-co njugated substituents that promote non-radiative transitions. We used two different methods to control the fluorescence lifetime in rhodamin e dyes with rigidized amino groups: (A) Substitution with benzyl deriv atives of different electron acceptor strength at the amino position. (B) Substitution of the carboxyphenyl group by phenyl groups with redu ced steric requirements and varying acceptor properties.