We present an in-depth investigation of cyclodextrin complexes with guest compounds featuring complexation-induced room temperature phosphorescence (RTP) in aqueous solution. Very interestingly, only the complexed regioisomers bearing lateral substituents on meta-position show RTP, whereas the stronger host-guest systems with para-substituted dyes show no RTP features. The reported systems were investigated regarding their complexation behavior in water using isothermal titration calorimetry and mass spectrometry. In the case of γ-CD very strong 1 : 1 inclusion complexes (Ka up to 5.13×105 M-1 ) were unexpectedly observed. It was found that not only a strong binding to the cyclodextrin cavity is needed to restrict motion, inducing the emission, but also the conformation inside the cavity plays a pivotal role - as supported by an extensive NMR study and MD simulations.
Keywords: cyclodextrins; host-guest systems; isothermal titration calorimetry; room temperature phosphorescence; supramolecular chemistry.
© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.