Substituent and environmental effects on the picosecond lifetimes of the polymethine cyanine dyes

Using the synchronously operated streak camera, the fluorescence lifetimes of polymethines of the cyanine family have been examined under low power CW picosecond dye laser excitation. The effects of steric hindrance on the lifetimes and of atomic substitution within the dyes have been measured, with lifetimes ranging from 14 ps to ∼ 2 ns. The strong viscosity-dependent fluorescence lifetime exhibited by these dyes has also been investigated. In addition, deviation from a Single exponential decay was recorded for several of the dyes.