Kai A. I. Zhang

Surface Area Control and Photocatalytic Activity of Conjugated Microporous Poly(benzothiadiazole) Networks

P-conjugated microporous polymers, such as organic semiconductors with additional porosity in the nanorange, are versatile materials. In addition to typical applications for high-surface-area materials, such as gas separation and storage, 3] conjugated polymer networks are also potential heterogeneous catalysts and can be used in optoelectronics and for energy applications. Given the importance of surface area and porosity, a simple methodology to influence these parameters is needed. In order to use conjugated polymer networks as catalysts and catalyst supports their chemical stability needs to be improved. Therefore we designed a stable, fully conjugated network by linking benzothiadiazole as a strong electron-withdrawing moiety through three Csp Csp bonds to benzene as a weak electrondonating component. The surface area of these novel conjugated microporous polymer networks could be adjusted by a simple synthetic protocol. Benzothiadiazole monomers have proven great stability towards oxidation in photovoltaic applications. The lowband-gap character, high absorption coefficient, and suitable energy levels of benzothiadiazole result in a very strong acceptor to be used in optoelectronic materials, such as lowband-gap polymers, 8] non-fullerene acceptors, or n-type field effect transistors. The combination of weak electron donors, such as a phenyl group with benzothiadiazole, may prevent a fast recombination of excitons and increase the yield of intersystem crossing to the triplet state of the polymer, thereby rendering it suitable for photosensitizing. Conjugated linear polymers with backbones based on the poly(phenylene ethynylene) structure or the polythiophene–porphyrin dyad repeat unit can generate singlet oxygen in water upon irradiation. Singlet oxygen is used for a number of applications, such as for treatment of waste water or in the synthesis of fine chemicals. An industrial process carried out on a scale of several tons a year is the photochemical oxidation of citronellol to rose oxide. Different dyes and transition metal complexes can generate singlet oxygen upon irradiation, and these sensitizers can be used in homogeneous solution or immobilized on a solid support. Working under heterogeneous conditions allows for easy separation of the sensitizer after reaction and reusability. Traditional systems suffer however from quenching of the produced singlet oxygen by the solid support, which reduces the quantum yield. Incorporation of a photosensitizing structure into a polymer backbone is particularly attractive, because no support to immobilize the sensitizer is needed when an insoluble photoactive polymer network is used. Therefore the ability of the conjugated microporous polymer (CMP) network to act as a singlet oxygen photosensitizer was evaluated by employing the oxidation of a-terpinene to ascaridole. The pore size and structure as well as specific surface area are beneficial in providing a high accessibility of exited solid polymer for solubilized oxygen, thus resulting in high efficiency for singlet oxygen generation in dependence of the pore architecture. A series of polymer networks based on benzothiadiazole as building block was synthesized through palladium-catalyzed Sonogashira–Hagihara cross-coupling polycondensation of 4,7-dibromobenzo[c][1,2,5]thiadiazole with 1,3,5-triethynylbenzen (Scheme 1).

Conjugated polymers containing diketopyrrolopyrrole units in the main chain

Summary Research activities in the field of diketopyrrolopyrrole (DPP)-based polymers are reviewed. Synthetic pathways to monomers and polymers, and the characteristic properties of the polymers are described. Potential applications in the field of organic electronic materials such as light emitting diodes, organic solar cells and organic field effect transistors are discussed.

Molecular Structural Design of Conjugated Microporous Poly(Benzooxadiazole) Networks for Enhanced Photocatalytic Activity with Visible Light

A simple structural design principle and band position alignment of conjugated microporous polymers for enhanced photocatalytic efficiency is presented. The valence and conduction band positions of the polymer networks can be fine-tuned by altering the substitution positions on the centered phenyl unit to match the required redox potential of the catalytic reactions under visible light.

Molecular Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Production by Photosynthesis

The search for metal-free organic photocatalysts for H2 production from water using visible light remains a key challenge. Reported herein is a molecular structural design of pure organic photocatalysts, derived from conjugated polybenzothiadiazoles, for photocatalytic H2 evolution using visible light. By alternating the substitution position of the electron-withdrawing benzothiadizole unit on the phenyl unit as a comonomer, various polymers with either one- or three-dimensional structures were synthesized and the effect of the molecular structure on their catalytic activity was investigated. Photocatalytic H2 evolution efficiencies up to 116 μmol h(-1) were observed by employing the linear polymer based on a phenyl-benzothiadiazole alternating main chain, with an apparent quantum yield (AQY) of 4.01 % at 420 nm using triethanolamine as the sacrificial agent.

Modification of conjugated microporous poly-benzothiadiazole for photosensitized singlet oxygen generation in water

Water-dispersible alkyne-bearing conjugated microporous poly-benzothiadiazoles were synthesized using thiol-yne chemistry to enhance water compatibility. The water compatible polymer networks were used as heterogeneous photocatalysts to generate singlet oxygen for the conversion of furoic acid to 5-hydroxy-2(5H)-furanone.

Highly porous conjugated polymers for selective oxidation of organic sulfides under visible light

High surface area porous conjugated polymers were synthesized via the high internal phase emulsion polymerization technique and micropore engineering as efficient heterogeneous photocatalysts for highly selective oxidation of organic sulfides to sulfoxides under visible light.

Conjugated Microporous Networks on the Basis of 2,3,5,6‐Tetraarylated Diketopyrrolo[3,4‐c]pyrrole

π-Conjugated microporous networks have been prepared from the tetraarylated diketopyrrolo[3,4-c]pyrrole unit as a tetrafunctional building block. The reactions are carried out using microwave-assisted Yamamoto or Sonogashira cross-coupling. Red insoluble powders are obtained, showing intense fluorescence. The polymer networks exhibit a high gas storage capability, with BET surface areas up to about 500 m2 · g−1.

π-Conjugated polyHIPEs as highly efficient and reusable heterogeneous photosensitizers

π-Conjugated microporous polyHIPEs are synthesized via Suzuki cross-coupling. The polymeric backbone consists of electron donor and acceptor moieties with suitable energetic characteristics to promote the efficient photosensitizing ability for the activation of singlet oxygen, showing extraordinarily high stability. The reaction can be carried out in a continuous flow reaction set-up, realizing complete conversion of α-terpinene into ascaridole.

Heterophase Photocatalysts from Water-Soluble Conjugated Polyelectrolytes: An Example of Self-Initiation under Visible Light

We herein report a new design route to stable, heterophase photocatalysts, which function as highly dispersible conjugated polymer nanoparticles and porous monoliths under visible light in aqueous medium. They were constructed by attachment of the ionic-liquid species 1-alkyl-3-vinylimidazolium bromide onto the side chains of a photoactive polymer. The structure configuration allows not only photocatalysis in aqueous environment but also a unique self-initiation radical cross-linking process to transform the water-soluble photoactive polymer into a heterophase system, either as nanoparticles or a porous monolith. High photocatalytic activity and reusability of the heterophase system were demonstrated in the degradation of organic dyes and reduction of Cr(VI) into Cr(III) in water under visible-light irradiation.

Well‐Defined and Monodisperse Linear and Star‐Shaped Quaterfluorene‐DPP Molecules: the Significance of Conjugation and Dimensionality

The synthesis of three new 1,4-diketo-3,6-diphenyl-pyrrolo[3,4-c]pyrrole (DPP) macromolecules appended with two or four quaterfluorene arms is reported. The compounds absorb mainly through the oligofluorene units and emit through the DPP core. Optical gain has been observed for Linear-c, a two-armed structure in which the quaterfluorene units are conjugated through the core unit.