Run Li

Structural Design Principle of Small‐Molecule Organic Semiconductors for Metal‐Free, Visible‐Light‐Promoted Photocatalysis

Herein, we report on the structural design principle of small-molecule organic semiconductors as metal-free, pure organic and visible light-active photocatalysts. Two series of electron-donor and acceptor-type organic semiconductor molecules were synthesized to meet crucial requirements, such as 1) absorption range in the visible region, 2) sufficient photoredox potential, and 3) long lifetime of photogenerated excitons. The photocatalytic activity was demonstrated in the intermolecular C-H functionalization of electron-rich heteroaromates with malonate derivatives. A mechanistic study of the light-induced electron transport between the organic photocatalyst, substrate, and the sacrificial agent are described. With their tunable absorption range and defined energy-band structure, the small-molecule organic semiconductors could offer a new class of metal-free and visible light-active photocatalysts for chemical reactions.

A fixed-bed photoreactor using conjugated nanoporous polymer-coated glass fibers for visible light-promoted continuous photoredox reactions

Here, we report on a fixed-bed photoreactor containing conjugated nanoporous polymer-coated glass fibers for visible light-promoted, heterogeneous photoredox reactions in a continuous flow system. A thin film of nanoporous polybenzothiadiazole with a thickness of ca. 80 nm was fabricated directly on the glass fiber with an effective catalyst content of ca. 3.2 wt%. The photocatalytic dehalogenation reaction of α-bromoacetophenones and the enantioselective α-alkylation of aldehydes were carried out in the fixed-bed photoreactor with comparable efficiencies to the state-of-art transition metal-based photocatalysts.

Asymmetric Covalent Triazine Framework for Enhanced Visible-Light Photoredox Catalysis via Energy Transfer Cascade

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.

Nanostructured Porous Polymers for Metal-Free Photocatalysis

The direct utilization of sunlight, especially the visible light part of solar spectrum as a clean and abundant energy source to activate organic reactions is a great challenge in organic chemistry and materials science. Beside the well-developed metal-based photocatalysts such as inorganic semiconductors or transition metal complexes, pure organic photocatalytic systems have gained much attention currently. Among metal-free photocatalysts, nanostructured and highly porous conjugated polymers are of particular interest due to their flexible tunability of optical and electronic properties. In this chapter, an overview on the development of this new class of functional materials is given. Various structural design methods such as donor–acceptor combination on the molecular level, band positions modification, and p/n character variation are shown, and porosity, morphology control and their impact on the photocatalytic efficiency are also described.