Effect of Controlling Thiophene Rings on D-A Polymer Photocatalysts Accessed via Direct Arylation for Hydrogen Production.

Conjugated polymer photocatalysts for hydrogen production have the advantages of an adjustable structure, strong response in the visible light region, adjustable energy levels, and easy functionalization. Using an atom- and step-economic direct C-H arylation method, dibromocyanostilbene was polymerized with thiophene, dithiophene, terthiophene, and fused thienothiophene and dithienothiophene, respectively, to produce donor-acceptor (D-A)-type linear conjugated polymers containing different thiophene derivatives with different conjugation lengths. Among them, the D-A polymer photocatalyst constructed from dithienothiophene could significantly broaden the spectral response, with a hydrogen evolution rate up to 12.15 mmol h-1 g-1. The results showed that the increase in the number of fused rings on thiophene building blocks was beneficial to the photocatalytic hydrogen production of cyanostyrylphene-based linear polymers. For the unfused dithiophene and terthiophene, the increase in the number of thiophene rings enabled more rotation freedom between the thiophene rings and reduced the intrinsic charge mobility, resulting in lower hydrogen production performance accordingly. This study provides a suitable process for the design of electron donors for D-A polymer photocatalysts.

Tunable Donor-Acceptor Linear Conjugated Polymers Involving Cyanostyrylthiophene Linkages for Visible-Light-Driven Hydrogen Production.

In this paper, an atom- and step-economic direct C-H arylation polymerization (DArP) strategy was developed to access cyanostyrylthiophene (CST)-based donor-acceptor (D-A) conjugated polymers (CPs) used for photocatalytic hydrogen production (PHP) from water reduction. The new CST-based CPs CP1-CP5 with varied building blocks were systematically studied by X-ray single-crystal analysis, FTIR, scanning electron microscopy, UV-vis, photoluminescence, transient photocurrent response, cyclic voltammetry measurements, and a PHP test, which showed that the phenyl-cyanostyrylthiophene-based CP3 exhibits a superior hydrogen evolution rate (7.60 mmol h-1 g-1) compared to other conjugated polymers. The structure-property-performance correlation results obtained in this study will provide an important guideline for the rational design of high-performance D-A CPs for PHP applications.

Terpolymerization strategy to achieve high-efficiency organic solar cells via construction of D1-A-D1-D2-type polymer donors.

Novel terpolymers were developed with ester group incorporation (BDT-2EST). DM1 with 5% BDT-2EST possesses suitable crystallinity and miscibility matching with Y6 acceptor to offer an excellent power conversation efficiency up to 17.21%. Moreover, the intertwined random features in DM1 offer robust photovoltaic performances with a broad molecular weight tolerance.

Tunable cyano substituents in D-A conjugated polymers accessed via direct arylation for photocatalytic hydrogen production.

2-Styrylthiophene-based donor-acceptor linear conjugated polymers with tunable cyano substituents are atom-economically obtained via direct C-H arylation for platinum-free photocatalytic hydrogen production, affording a HER of up to 9.79 mmol h-1 g-1.

C-H Direct Arylation: A Robust Tool to Tailor the π-Conjugation Lengths of Non-Fullerene Acceptors.

Facile synthesis without involvement of toxic reagents is of great significance in the practical application of photovoltaic materials. In this work, four acceptor-donor-acceptor (A-D-A) type unfused-ring acceptors (UFRAs) with stepwise extension in π-conjugation, i. e., CPFB-IC-n (n=1-4), involving cyclopentadithiophene (CPDT) and 1,4-difluorobenzene (DFB) as cores, are facilely synthesized by an atom-, step-economic and labor-saving method through direct arylation of C-H bond (DACH). Among them, CPFB-IC-4 has the longest conjugation lengths among the molecular UFRA ever reported. The dependence of optoelectronic properties and photovoltaic performances of CPFB-IC-n (n=1-4) on conjugation length were systematically investigated. CPFB-IC-2 with near zero highest occupied molecular orbital (HOMO) offsets (ΔEHOMO =0.06 eV) achieves the highest power conversion efficiency (PCE), due to the significantly enhanced open voltage (VOC ) and short current (JSC ) caused by the balanced frontier molecular orbitals (FMOs) and complementary light absorption. Our work demonstrates that the optical properties and FMOs of UFRAs can be finely tuned by the stepwise elongation of conjugation lengths. Meanwhile, DACH coupling as a powerful tool here established will be a promising candidate for synthesizing high-performance oligomeric UFRAs.

Tuning the activity of the inert MoS2 surface via graphene oxide support doping towards chemical functionalization and hydrogen evolution: a density functional study.

The basal plane of MoS2 provides a promising platform for chemical functionalization and the hydrogen evolution reaction (HER); however, its practical utilization remains challenging due to the lack of active sites and its low conductivity. Herein, using first principles simulations, we first proposed a novel and effective strategy for significantly enhancing the activity of the inert MoS2 surface using a graphene oxide (GO) support (MoS2/GOs). The chemical bonding of the functional groups (CH3 and NH2) on the MoS2-GO hybrid is stronger than that in freestanding MoS2 or MoS2-graphene. Upon increasing the oxygen group concentration or introducing N heteroatoms into the GO support, the stability of the chemically functionalized MoS2 is improved. Furthermore, use of GOs to support pristine and defective MoS2 with a S vacancy (S-MoS2) can greatly promote the HER activity of the basal plane. The catalytic activity of S-MoS2 is further enhanced by doping N into GOs; this results in a hydrogen adsorption free energy of almost zero (ΔGH = ∼-0.014 eV). The coupling interaction with the GO substrate reduces the p-type Schottky barrier heights (SBH) of S-MoS2 and modifies its electronic properties, which facilitate charge transfer between them. Our calculated results are consistent with the experimental observations. Thus, the present results open new avenues for the chemical functionalization of MoS2-based nanosheets and HER catalysts.

A multifunctionalized strategy of indoles to C2-quaternary indolin-3-ones via a TEMPO/Pd-catalyzed cascade process.

A method for combinative oxidative homo dimerization and cyanomethylation of free indole derivatives catalysed by TEMPO and Pd(OAc)2 was demonstrated for the first time. This new methodology is both atom and step efficient and is applicable to a broad scope of substrates, allowing the synthesis of a range of synthetically valuable 2-(2-(1H-indol-3-yl)-3-oxoindolin-2-yl)acetonitriles in moderate to excellent yields.

Highly efficient synthesis of 2,5-disubstituted pyrazines from (Z)-ß-haloenol acetates.

A highly efficient synthesis of a wide range of 2,5-disubstituted pyrazines from (Z)-ß-haloenol acetates is described. The reactions are conducted under convenient conditions and provide products with excellent regioselectivity in moderate to excellent yields with a broad substrate scope, including a variety of aromatic and aliphatic haloenol acetates.

(Z)-1,4-Diphenyl-but-1-en-3-ynyl acetate.

The title compound, C(18)H(14)O(2), is almost planar with a dihedral angle of 1.24 (2)° between the phenyl-ethynyl and styryl groups. The acet-oxy group is tilted by 82.46 (2) and 82.26 (3)° with respect to the benzene ring planes.

A general and simple diastereoselective reduction by L-Selectride: efficient synthesis of protected (4S,5S)-dihydroxy amides.

A general approach to (4S,5S)-4-benzyloxy-5-hydroxy-N-(4-methoxybenzyl) amides 10 based on a diastereoselective reduction of (5S,6RS)-6-alkyl-5-benzyloxy-6-hydroxy-2-piperidinones 6 and their tautomeric ring-opened keto amides 7 is described. The reduction with L-Selectride at -20 degrees C to room temperature afforded the products 10 in excellent yields and moderate to high syn-diastereoselectivities.