Tunable Conjugated Organoborane Oligomers for Visible-Light-Driven Hydrogen Evolution

A series
of linear conjugated organoborane oligomers are synthesized
here by introducing electron-deficient borole units to the well-explored
thiophene unit of variable length. It is found that the photophysical
properties, particularly the band structures of products, alter regularly
with the extension of thiophene. Interestingly, such oligomers exhibit
high activity for photocatalytic hydrogen evolution under visible
light (λ > 420 nm), outperforming most of the reported linear
polymers. The enhanced performance is possibly attributed to the strong
electron-accepting nature of the borole group, as well as the good
electron donor and light-harvesting properties of the thiophene group.
The combination of these two units facilitates charge separation of
oligomers, thus allowing the participation of as many photogenerated
charge carriers as possible in the desired water reduction reaction.
The results indicate the success of our strategy and the importance
of rational molecular design for developing conjugated (oligo)­polymers
for efficient photocatalytic hydrogen evolution.