Redox and Coordination Chemistry of Chalcogenophenes

Chalcogenophene is a five membered aromatic ring containing group 16 elements, and widely used for the design of small molecule or polymer based organic devices. In this work, we report a thorough discussions on the electrochemical redox chemistry of chalcogenophenes, with special emphasis on tellurophene (N. Shida, H. Nishiyama, F. Zheng, S. Ye, D. S. Seferos, I. Tomita, S. Inagi, Communications Chemistry, 2019, 2, 124.). 2,5-Diphenyl tellurophene (PT) was first chosen as a model molecule for this study (Figure). By employing spectroelectrochemstry, electroorganic synthesis and quantum simulations techniques, it was revealed that PT change their redox behavior in two different modes: one electron oxidation to generate radical cation in weakly coordinating electrolyte or two electron oxidation with coordination of anions and solvents onto tellurium in coordinating electrolyte. The strong interaction between anions (ClO4, BF4, PF6) or neutral donor (MeCN) with tellurium in oxidized tellurophenes became evident for the first time, which implies that the positive charge is not delocalized in the conjugated π-system as is usually expected for the conjugated molecules. By using analogous molecule with larger π-system, i.e., 2,5-(9,9-dimethylfluorene)tellurophene (FT), coordinated species and radical cation were generated simultaneously. These finding will lead further understanding of the fundamental redox chemistry of chalcogenophenes. Figure 1