Exploring Benzothieno[3,2‐b]benzothiophene S‐Oxides for Organic Electronics, Fluorescence‐Based Applications, and Asymmetric Synthesis

A series of benzothieno[3,2-b]benzothiophene S-oxides has been efficiently synthesized via one- or two-step selective oxidation of benzothieno[3,2-b]benzothiophene (BTBT). These BTBT S-oxides form highly ordered structures that display optical anisotropy, are thermally stable up to temperatures above 210 oC, and do not show phase transitions. They exhibit long excited state lifetimes (0.181-0.869 ms) and are more resistant to oxidative degradation than their parent unoxidized BTBT. Some of these compounds demonstrate high quantum yields, exceeding 98% in solution and 71% in the solid state. As evidenced by quantum-chemical calculations, BTBT-based sulfoxides have sufficiently high pyramidal inversion energy barriers that prevent their stereomutation at room temperature. Additionally, fully S-oxidized BTBT meets the energy-splitting criterion required for the singlet fission process, with the T1 energy level that makes it suitable for device application.