Researchers at Kyushu University and The University of Tokyo developed an ionic photocatalytic system using a novel counteranion, BBcat, which captures basic substrates and holds them near a ruthenium complex. Published on Oct. 8, 2026, in Chemical Science, the innovation maintains high yields in dilute solutions.
Researchers at Kyushu University, working alongside The University of Tokyo, have developed a photocatalytic system that uses a newly created counteranion called BBcat to capture reacting molecules and hold them close to active energy-absorbing sites. Published on Oct. 8, 2026, the work addresses a fundamental limitation in light-driven chemistry: maintaining high reaction rates when reactants are scarce in dilute solutions.
BBcat Counteranion Captures Reactants
Photocatalysis uses light to drive chemical reactions. In standard systems, energy transfer depends entirely on collisions between an excited photocatalyst and reacting molecules.
When those molecules are present at low concentrations, collisions happen less frequently, causing reactions to slow down.
Professor Takanori Iwasaki led a team from Kyushu University’s Faculty of Engineering in pairing a light-absorbing ruthenium complex with BBcat. Counteranions are negatively charged ions that accompany positively charged ions in ionic compounds, traditionally valued for their electron-donating abilities. However, BBcat functions simultaneously as a Lewis acid and an anion, meaning it can accept electron pairs. Instead of repelling basic molecules, the BBcat-based counteranion binds them.
Imparting strong acidity to an anion makes it possible to move beyond the conventional view of anions as bases and use the photocatalyst’s counteranion itself as a substrate-recognition site.
Comparing Yields in Dilute Conditions
Under standard test conditions, the BBcat-based catalyst achieved a 76% yield, compared to just 24% for a conventional catalyst paired with a different counteranion when tested by the research team using [2+2] photocycloaddition, a reaction where light helps two molecules form a four-membered carbon ring.
| Catalyst System | Standard Yield | Dilute Yield |
|---|---|---|
| BBcat-based catalyst | 76% | 75% |
| Conventional catalyst | 24% | 9% |
The conventional catalyst’s yield dropped sharply to 9% under dilution, while the BBcat system maintained a 75% yield.
Extending BBcat to Other Transition Metal Catalysts
According to Iwasaki, introducing BBcat requires only simple mixing, allowing the selective transformation and reaction rate acceleration functions driven by BBcat to be readily combined with other transition metal catalysis.