A novel 1,1,6,6-tetracyano hexatriene linked conjugated microporous polymer for high photocatalytic hydrogen evolution

Abstract

We report the synthesis of a novel 1,1,6,6-tetracyanohexatriene (TCHT) linked conjugated microporous polymer (TCHT-P), through a double [2 + 2] cycloaddition–retroelectrocyclization (CA–RE) reaction of tetracyanoethylene with tris(4-ethynylphenyl) amine. Strong D–A interactions in TCHT-P lead to broad, near-infrared (NIR) absorption extending the red-edge to ∼1230 nm and to radical character. TCHT-P, as a photocatalyst in a water splitting reaction with a Pt co-catalyst, demonstrated an exceptional hydrogen evolution rate of 32 000 µmol g⁻¹ in 12 hours. The outstanding photocatalytic performance of the polymer originates from strong D–A interactions and nitrile functional groups, which significantly enhance hydrophilicity, charge separation efficiency, and co-catalyst binding. The spatial separation of photogenerated electrons and holes at distinct donor and acceptor sites leads to effective charge accumulation and a dramatic improvement of overall solar-to-hydrogen conversion efficiency. A 1,1,4,4-tetracyanobutadiene integrated reference polymer (TCBD-P) showed a red-edge at ∼1050 nm, a band gap of 1.60 eV, and photocatalytic hydrogen production of 11 000 µmol g⁻¹ in 12 hours, highlighting the superiority of TCHT linkages. To our knowledge, these are the first examples of TCBD/TCHT-integrated polymers reported for HER studies.