Cyanines with unsymmetric donor groups are investigated by steady state and
time-resolved fluorescence measurements. Several chemically ridigized deri
vatives are compared, and their synthesis is described. In several cases, r
igidization leads to an increase of the nonradiative decay rate constants.
This unusual behaviour is explained within a model of multiple emissive sta
tes. (C) 1999 Elsevier Science S.A. All rights reserved.