Nanostructured Lateral Boryl Substitution Conjugated Donor–Acceptor Oligomers for Visible‐Light‐Driven Hydrogen Production

Abstract

Poor charge separation is the main factor that limits the photocatalytic hydrogen generation efficiency of organic conjugated polymers. In this work, a series of linear donor–acceptor (D–A) type oligomers are synthesized by a palladium‐catalyzed Sonogashira–Hagihara coupling of electron‐deficient diborane unit and different dihalide substitution sulfur functionalized monomers. Such diborane‐based A unit exerts great impact on the resulting oligomers, including distinct semiconductor characters with isolated lowest unoccupied molecular orbital (LUMO) orbits locating in diborane‐containing fragment, and elevated LUMO level higher than water reduction potential. Relative to A‐A type counterpart, the enhanced dipole polarization effect in D–A oligomers facilitates separation of photogenerated charge carriers, as evidenced by notably prolonged electron lifetime. Owing to π–π stacking of rigid backbone, the oligomers can aggregate into an interesting 2D semicrystalline nanosheet (≈2.74 nm), which is rarely reported in linear polymeric photocatalysts prepared by similar carbon–carbon coupling reaction. Despite low surface area (30.3 m2 g−1), such ultrathin nanosheet D–A oligomer offers outstanding visible light (λ > 420 nm) hydrogen evolution rate of 833 µmol g−1 h−1, 14 times greater than its A‐A analogue (61 µmol g−1 h−1). The study highlights the great potential of using boron element to construct D–A type oligomers for efficient photocatalytic hydrogen generation.

Arylboron functional covalent organic frameworks for synergistic photocatalytic hydrogen evolution

“…Recently, our group reported a series of D–A type oligomers or polymers embedded with arylboron acceptors, which exhibited high photocatalytic performance under visible light irradiation ( λ > 420 nm) because of the positive influence of arylboron units. 29–31 This aroused our interest in studying triarylboron as a functional group of COFs for photocatalytic HER.…”

Molecular Hyperpolarization-Directed Photothermally Enhanced Melanin-Inspired Polymers

“…People are calling for the development of renewable energy technologies to reduce the pressure on our living environment and energy supply. − As an inexhaustible clean energy, solar energy has received widespread attention. − To efficiently convert solar energy into other kinds of usable energy, the design of conversion materials is the key issue, and increasing the light absorption capacity of materials is always highly desirable. − Constructing the donor–acceptor (D–A) conjugate structures is a common molecular design strategy in the field of organic optoelectronics. The chemical connection between strong acceptor and donor building blocks can significantly offer numerous types of D–A pairs, which would greatly change the polarizability and dipole moment of the local molecule structures and induce the re-hybridization of molecular orbitals. − Molecular orbital re-hybridization could further lead to the decrease of the lowest unoccupied molecular orbital (LUMO) as well as the increase of the highest occupied molecular orbital (HOMO) within the system, thereby reducing the molecular optical bandgap. The migration of electrons would tend to move from a higher HOMO to lower LUMO, which will induce the red shift of the total light absorption spectrum.…”

Effect of D/A Ratio on Photocatalytic Hydrogen Evolution Performance of Conjugated Polymer Photocatalysts

“…However, it critically relies on efficient photocatalyst semiconductor materials for proton reduction. Most previously developed photocatalysts are inorganic semiconductor materials, which often suffer from large band gaps, low visible light utilization, difficulty in precise tuning by rational structural design, etc. − Recently, organic conjugated polymers have attracted great attention due to their unique advantages, such as tunable optical absorption and electronic properties, easily tunable skeleton structure and porosity, and high photostability and strong economic applicability, mainly including the family of g-C 3 N 4 , − conjugated microporous polymers (CMPs), − covalent triazine-based frameworks (CTFs), − covalent organic frameworks (COFs), − and linear conjugated polymers. − However, most organic photocatalysts still face low photocatalytic activity and low apparent quantum yield (AQY) due to the rapid recombination of photogenerated electrons/holes. To further improve the photocatalytic activity of organic polymer systems, it is necessary to develop new organic photocatalysts and fine-tune their electronic properties to obtain better photocatalytic activity.…”