Non-radiative decay in rhodamines: Role of 1:1 and 1:2 molecular complexation with β-cyclodextrin

The radiationless rate constants in both 1:1 complexes with either rhodamine reflect essentially the activated charge transfers which are enhanced to kA = (1.1-1.4) × 109 s−1 as compared to 1:2 complexes of kA = (7.5-7.8) × 107 s−1. The difference in one order of magnitude is assigned to the specificity of the binding sites and geometry constraints in each case.