Two methoxycarbonyl-substituted 2,5-di(1,3-dithiol-2-ylidene)-1,3-dithiolane-4-thione derivatives with alkylsulfanyl groups of different sizes were synthesized, and their redox and electronic properties and crystal structures were investigated. The difference in the solid-state absorption spectra occurs because of differences in the intermolecular interactions caused by their molecular packings.

N-propylsulfanyl and isopropylsulfanyl substituted 2,5-di(1,3-dithiol-2-ylidene)-1,3-dithiolane-4-thione derivatives with methoxycarbonyl groups were synthesized, and their redox and electronic properties and crystal structures were investigated. Solid-state absorption spectra showed that both derivatives absorb almost all visible light. Furthermore isopropylsulfanyl-substituted derivatives absorb near-infrared light and the absorption edge reaches around 1320 nm. The crystal structures show that both derivatives are stacked in one dimension to form a columnar structure, but the molecular arrangements of their columns were quite different from each other. The stacked n-propylsulfanyl derivatives kept their orientation of thiocarbonyl groups in the same direction and the one molecule of the isopropylsulfanyl derivatives were rotated in relation to each other by an angle of 56° about their longer molecular axis. The TD-DFT calculation of stacked molecules suggests that the molecular arrangement among the stacked molecules affects the maximum absorption in near-infrared region.