Probing Basic Properties of Zeolites with Charge-Transfer Complexes of Aromatic Donor–Acceptor Pairs Formed Inside the Cavities

Spectroscopic properties were investigated of the charge-transfer (CT) complexes of electron-accepting 1,2,4,5-tetracyanobenzene (TCNB) with arene donors assembled inside the cavities of various alkali metal-exchanged faujasite zeolites. It was found that the peak position of the CT absorption bands blue-shifted depending on the basicity of the zeolites originating from the exchanged cations. The Stokes shift, the separation between the peak energies of absorption and emission was larger in more basic zeolites and linearly correlated with the basicity. TCNB–arene CT complexes were found to be a promising candidate for probing the basicity of the zeolites.