Cyclodextrins (CD) are cyclic oligosaccharides consisting of six or more D-glucopyranose units, the interior of which forms a hydrophobic cavity. In the present study, we employed the CD confinement effects as a tool to suppress an electronic decoherence of guest wavefunction by reducing intermolecular interactions between a guest molecule and the surrounding environment.Effects of host/guest stoichiometry on the decoherence suppresion were investigated by comparing native -CD with trimethyl--CD that should form only a 1:1 complex. Both fluorecence and fluorecence-excitation spectra of inclusion complexes exhibited spectral narrowings only for the -CD host, suggesting that the formation of barrel-type -CD dimer plays a key role for the pronounced spectral narrowings.