A radical cation, generated from an extended it-conjugated thiophene 6-mer composed of four ethynylene-thienylene and two vinylene-thienylene units, was observed to form a stable three-dimensional pi-dimer containing 70 pi-electrons. The pi-dimer prepared in solution was investigated by using magnetic circular dichroism (MCD), ESR spectroscopy, and UV-vis-NIR absorption spectroscopy. Probing the individual NIR absorption bands showed that the MCD signals can be assigned to the pseudo Faraday A term, indicating that the absorption bands are comprised of nearly degenerate electronic transitions. X-ray crystallographic analysis revealed that the pi-dimer has a three-dimensional face-to-face and continuous pi-conjugated donutlike structure. Analysis of the UV-vis-NIR and ESR spectra of the pi-dimer in the solid state confirmed that it possesses the dimer structure. The prediction made by using TD-DFT calculations that the dimer would have a 70 pi-electron diatropic nature was confirmed by using solid state NMR spectroscopy.