Intersystem crossing rate constants of rhodamine dyes: influence of the amino-group substitution

A time-resolved laser-scanning-microscopy technique is described. Using this technique we measured intersystem crossing rate constants of structurally related rhodamine dyes. Although rhodamine dyes are distinguished by a low probability of intersystem crossing (<1%), the results can be presented with high accuracy. The relationship between the triplet quantum yield and molecular structure was investigated. In contrast to the fluorescence quantum yield, the rate constant of intersystem crossing is not influenced by the substitution of the amino groups.