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Steady-state and time-resolved studies on the emission properties of three 7-(diethy1amino)coumarin laser dyes in aqueous y-cyclodextrin (7-CD) solutions are reported. On addition of y-CD, fluorescence maxima of all the three dyes shift to higher energy, with a huge enhancement of the yield of intramolecular charge transfer (ICT) emission for the flexible ones (I and 11) and a very slight enhancement for the rigid analogue 111. The results are explained in terms of the concept of polarity-dependent twisted ICT rates. It is proposed that twisted ICT, the main nonradiative process in the excited ICT states of these dyes, is severely restricted inside the y-cyclcdextrin cavity because of the reduced polarity. This is responsible for the enhancement of fluorescence from the ICT state.

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