Regulating Charge‐Transfer in Conjugated Microporous Polymers for Photocatalytic Hydrogen Evolution

Abstract

Bandgap engineering in donor–acceptor conjugated microporous polymers (CMPs) is a potential way to increase the solar‐energy harvesting towards photochemical water splitting. Here, the design and synthesis of a series of donor–acceptor CMPs [tetraphenylethylene (TPE) and 9‐fluorenone (F) as the donor and the acceptor, respectively], F0.1CMP, F0.5CMP, and F2.0CMP, are reported. These CMPs exhibited tunable bandgaps and photocatalytic hydrogen evolution from water. The donor–acceptor CMPs exhibited also intramolecular charge‐transfer (ICT) absorption in the visible region (λmax=480 nm) and their bandgap was finely tuned from 2.8 to 2.1 eV by increasing the 9‐fluorenone content. Interestingly, they also showed emissions in the 540–580 nm range assisted by the energy transfer from the other TPE segments (not involved in charge‐transfer interactions), as evidenced from fluorescence lifetime decay analysis. By increasing the 9‐fluorenone content the emission color of the polymer was also tuned from green to red. Photocatalytic activities of the donor–acceptor CMPs (F0.1CMP, F0.5CMP, and F2.0CMP) are greatly enhanced compared to the 9‐fluorenone free polymer (F0.0CMP), which is essentially due to improved visible‐light absorption and low bandgap of donor–acceptor CMPs. Among all the polymers F0.5CMP with an optimum bandgap (2.3 eV) showed the highest H2 evolution under visible‐light irradiation. Moreover, all polymers showed excellent dispersibility in organic solvents and easy coated on the solid substrates.

Sulfonated Hyper‐cross‐linked Porous Polyacetylene Networks as Versatile Heterogeneous Acid Catalysts

“…The poly(arylene ethynylene)‐type PPCs functionalized with Tröger's base ( S BET =750 m 2 ⋅ g −1 ) were prepared from 1,3,5‐triethynylbenzene and diiodinated Tröger's base monomers through direct step‐growth polymerization performed by means of Sonogashira coupling . The direct copolymerization through Suzuki‐Miyaura coupling and tetrakis(4‐bromophenyl)ethane, 2,7‐dibromo‐9‐fluorenone, and 1,4‐benzene diboronic acid comonomers were used to prepare donor‐acceptor PPCs highly efficient towards hydrogen evolution . In the case of the above‐mentioned PPCs prepared by direct polymerizations, the organometallic or heteroatomic segments of the PPCs served not only as catalytically active centres, but simultaneously participated (as the rigid network struts) in the formation of the porous texture of the PPCs.…”

“…[20] The direct copolymerization through Suzuki-Miyaura coupling and tetrakis(4-bromophenyl) ethane, 2,7-dibromo-9-fluorenone, and 1,4-benzene diboronic acid comonomers were used to prepare donor-acceptor PPCs highly efficient towards hydrogen evolution. [21] In the case of the above-mentioned PPCs prepared by direct polymerizations, the organometallic or heteroatomic segments of the PPCs served not only as catalytically active centres, but simultaneously participated (as the rigid network struts) in the formation of the porous texture of the PPCs. This positively influenced the specific surface area of PPCs.…”

Realizing high hydrogen evolution activity under visible light using narrow band gap organic photocatalysts

“…Recently, conjugated organic semiconductors have attracted much attention as photocatalysts for hydrogen generation because of their potential advantages such as flexible molecular structure, tuneable electronic property and band gap. [6][7][8][9][10][11][12] The representative organic polymer photocatalysts mainly include linear conjugated polymers (CPs), [13][14][15][16][17][18][19] graphitic carbon nitrides (g-C 3 N 4 ), 20,21 conjugated microporous polymers (CMPs), [22][23][24][25][26][27] crystalline covalent organic frameworks (COFs), [28][29][30][31][32][33] and covalent triazine-based frameworks (CTFs). [34][35][36][37][38][39] It has been proved that the selectivity of a suitable building block is important to improve the photocatalytic activity of organic polymer photocatalysts, and many studies have demonstrated that dibenzothiophene-S,S-dioxide with strong electron accepting ability is an efficient building block to generate organic polymer photocatalysts with high photocatalytic activity.…”

Bimodal Heterogeneous Functionality in Redox‐Active Conjugated Microporous Polymer toward Electrocatalytic Oxygen Reduction and Photocatalytic Hydrogen Evolution

“…Moreover, redox‐active CMPs were also found to be capable of in situ generation and stabilization of metal nanoparticles (NPs), and subsequently, such metal nanoparticle stabilized CMP (NP@CMP) materials have shown significantly improved electrocatalytic activities . Furthermore, organic porous materials have been explored recently as heterogeneous catalysts for the photochemical H 2 evolution reaction . However, improvements in both these processes in a cost‐effective manner are important challenges for the scientific community .…”

“…[22,41] Furthermore, organic porousm aterials have been exploredr ecently as heterogeneous catalysts for the photochemical H 2 evolution reaction. [48][49][50][51][52][53][54] However, improvements in both these processes in ac ost-effectivem anner are importantc hallenges for the scientificc ommunity. [55] To the best of our knowledge,C MP materials with bimodal functionality that can catalyze both the electrochemical ORR and the photochemical H 2 evolutionr eactiona re yet to be documented.…”