N-heterocyclic carbene boranes as electron-donating and electron-accepting components of π-conjugated systems.

Give and take: The introduction of NHC-borane moieties to thiophene-based π skeletons endows a zwitterionic character, which makes the π system electron-donating, while the NHC ring acts as an electron-accepting moiety. The NHC-borane-substituted thiophene underwent a clean photoisomerization with a drastic color change, however, the expanded bithiophene derivatives were inert to this photoreaction, showed low oxidation potentials, and formed a slipped π-stacked array in the crystal.