The complexation behavior of zinc (II) tetraphenylporphyrin-viologen covalently linkedcompounds by a polymethylene chain (ZnPCnV2+; n = 4–9) withtri-O-methyl-β-cyclodextrin (TM-β-CD) was investigated by meansof 1H NMR and UV/Vis absorption spectrometry in acetonitrile-water (1:1, v/v).The 1H NMR spectra indicated that ZnPCnV2+ existed as a mixture ofa dimer and a monomer at high concentration (>1 × 10-3 M). The dimerwas degraded to the monomer upon complexation with TM-β-CD involving theformation of 1:1 and 1:2 (ZnPCnV2+: TM-β-CD) complexes, whichwas observed by UV/Vis spectrometry. Furthermore, 1H NMR spectra exhibitedthat there are at least two types of structures for these complexes, one is a fastexchanging complex, and another is a slow exchanging one. A slow exchanging complexcould be assigned as a rotaxane type structure in which the methylene chain moiety ofZnPCnV2+ penetrated into the cavity of TM-β-CD. Discrete formationconstants for these complexes were evaluated. The values were little affected by the spacermethylene chain length (n ≥ 7).