Dual luminescence of dimethylaminobenzonitrile in γ-cyclodextrin. Environmental effects on twisted intramolecular charge-transfer phenomenon

Abstract

Steady-state absorption and emission spectra of p-N,N-dimethylaminobenzonitrile (DMABN) have been studied in aqueous γ-cyclodextrin (γ-CD) solutions. Two kinds of DMABN: γ-CD complexes with distinctly different excitation spectra are observed. For complexes in which the DMABN molecule is totally enclosed inside the γ-CD cavity, the twisted intramolecular charge transfer (TICT) is severely suppressed with a corresponding large enhancement of the ‘non-polar’ emission, while for partially enclosed DMABN molecules the TICT emission is only slightly enhanced. The fact that the TICT is inhibited inside the very large γ-CD cavity conclusively proves that the TICT phenomenon is polarity controlled.