The redox chemistry of supramolecular nanotubes self-assembled from amphiphilic cyanine dye 3,3′-bis(2-sulfopropyl)-5,5′,6,6′- tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) in aqueous solution was investigated by spectroelectrochemistry. The absorption spectra during the redox-reaction were analyzed by singular value decomposition (SVD) and semiempirical quantum mechanical calculations. Previously unavailable absorption spectra were modeled for each species of the reaction at every point throughout the oxidation and reduction process. The expected peak absorption wavelengths of these species present throughout the electrochemical cycles were calculated using the semiempirical method ZINDO/S (Zerner method of intermediate neglect of differential overlap for spectroscopy). The spectral assignments from the proposed species derived from the SVD analysis were confirmed with the ZINDO/S calculations, supporting the assignment of the key species as well as the intermediates in the proposed redox-reaction scheme. The oxidized species have spectral signatures that agree with the calculated spectral maxima of isolated species, indicating that the resulting products are not electronically perturbed by aggregation, in strong contrast to the unoxidized dye.