THE ISTED-INTRAMOLECULAR-CHARGE-TRANSFER-STATE-FORMING COMPOUND AS A GUEST FOR CYCLODEXTRINS

Spectral luminescence behaviour of N-methyl-p-(p-dimethylaminophenyl)- pyridinium (APP) iodide in aqueous alpha- and beta-cyclodextrin (CD) s olutions has been studied. The inclusion complex formation of most pro bably 1:1 constitution was established with binding constant K of abou t 400 M-1 for beta-CD. The inclusion of APP is far less favourable for alpha-CD (K=7 M-1) than for beta-CD. The data obtained confirm the su ggestion that the APP cation is able to form the twisted intramolecula r charge transfer (TICT) state upon excitation. The inclusion host-gue st complex formation of APP with alpha- and beta-CD is inferred to cau se the non-TICT fluorescence quantum yield enhancement by factors of 1 .3 and 3.33 respectively, and to hamper the TICT state formation mainl y through spatial restriction experienced by the guest molecule within the CD cavity. The ability of the CD complexation to assist in indent ifying the guest's excited state nature has thus been demonstrated.