Molecular interaction between 1,4-benzenedithiol and 1,4-diethynylbenzene

Molecular interactions of 1,4-benzenedithiol (BDT) and 1,4-diethynylbenzene (DEB) were studied in hexane or in toluene at 23–25°C by a UV-spectroscopy to elucidate the mechanism for the polyaddition of BDT to DEB. The solution containing both BDT and DEB showed a broad absorption at 280–380 nm. The magnitude of the absorbance gradually increased during storage of the solution. Both BDT and DEB may have molecular interactions in solution and also in the solid state to make complexes of the charge–transfer (CT) type. The equilibrium constant (K) and extinction coefficient (e) were tentatively estimated to be about 40 and 8000–15000 at 310 nm in hexane or 5:8 and 8000 in toluene, respectively, at 5 s after mixing the component solutions. As a model system, spectroscopic investigation was also made with systems of thiophenol (TP)–phenylacetylene (PA), TP–DEB and BDT–PA in hexane. These systems exhibited a large equilibrium constant and large extinction coefficient as well as BDT and DEB. Consequently, CT interactions seem to control the polyaddition of BDT to DEB in solution and also in solid state.