The formation of
aldehydes and ketones via selective oxidation
of alcohols is an essential transformation in organic synthesis. However,
the usually harsh reaction conditions using toxic metal catalysts
or corrosive reagents lead to undesired side products and wastes.
Environmentally friendly and mild reaction conditions using metal-free
catalysts remain a huge challenge. Herein, we report the use of a
thiophene-based covalent triazine framework (CTF) as pure organic
and visible-light-active photocatalyst for the selective oxidation
of alcohols at room temperature. Molecular oxygen was activated as
a clean and selective oxidant. The high selectivity and efficiency
of the pure organic photocatalyst could be demonstrated and were comparable
to those of the state-of-art metal or nonmetal catalytic systems reported.
Conjugated polymers have emerged as promising candidates for photocatalytic H2 production owing to their structural designability and functional diversity. However, the fast recombination of photoexcited electrons and holes limits their H2 production rates. We have now designed molecular heterostructures of covalent triazine frameworks to facilitate charge‐carrier separation and promote photocatalytic H2 production. Benzothiadiazole and thiophene moieties were selectively incorporated into the covalent triazine frameworks as electron‐withdrawing and electron‐donating units, respectively, by a sequential polymerization strategy. The resulting hybrids exhibited much improved charge‐carrier‐separation efficiency as evidenced by photophysical and electrochemical characterization. An H2 evolution rate of 6.6 mmol g−1 h−1 was measured for the optimal sample under visible‐light irradiation (λ>420 nm), which is far superior to that of most reported conjugated‐polymer photocatalysts.
Complex multiple-component semiconductor photocatalysts can be constructed that display enhanced catalytic efficiency via multiple charge and energy transfer, mimicking photosystems in nature. In contrast, the efficiency of single-component semiconductor photocatalysts is usually limited due to the fast recombination of the photogenerated excitons. Here, we report the design of an asymmetric covalent triazine framework as an efficient organic single-component semiconductor photocatalyst. Four different molecular donor-acceptor domains are obtained within the network, leading to enhanced photogenerated charge separation via an intramolecular energy transfer cascade. The photocatalytic efficiency of the asymmetric covalent triazine framework is superior to that of its symmetric counterparts; this was demonstrated by the visible-light-driven formation of benzophosphole oxides from diphenylphosphine oxide and diphenylacetylene.
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