Conjugated Building Blocks Based on Electron-Deficient Thiaborin S-Oxides

Boron-doped pi-conjugated materials have generated interest owing to their interesting photophysical properties derived from the empty p-orbital on boron. In particular, the electron-accepting properties of triarylborane units are useful for the development of electron-deficient pi-conjugated materials such as organic n-type semiconductors. On the other hand, sulfones and sulfoxides are also electron-deficient species that can be easily prepared by oxidation of the corresponding sulfides. In this work, we prepared new thiophene-fused thiaborin conjugated building blocks with different oxidation states of the sulfur atom. The new building blocks possess distinct photophysical properties that are dependent on the oxidation state of the sulfur atom. In particular, the sulfone compound exhibits a LUMO energy level that is markedly lower than those of the corresponding dithienylborane and dithienylthiophene S,S-dioxide, suggesting that the combination of boron and sulfone enhances the electron-accepting properties. In addition, the sulfone unit can be modified by the Stille cross-coupling reaction, demonstrating its potential use in other functional p-pi* conjugated materials.