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 beta-CD with trimethyl-beta-CD that should form only a 1: 1 complex. Both fluorecence and fluorecence-excitation spectra of inclusion complexes exhibited spectral narrowings only for the beta-CD host, suggesting that the formation of barrel-type beta-CD dimer plays a key role for the pronounced spectral narrowings.