Iodine passivation facilitates on-surface synthesis of robust regular conjugated two-dimensional organogold networks on Au(111).

Two-dimensional conjugated organogold networks with anthra-tetrathiophene repeat units are synthesized by thermally activated debrominative coupling of 2,5,9,12-tetrabromoanthra[1,2-b:4,3-b':5,6-b'':8,7-b''']tetrathiophene (TBATT) precursor molecules on Au(111) surfaces under ultra-high vacuum (UHV) conditions. Performing the reaction on iodine-passivated Au(111) surfaces promotes formation of highly regular structures, as revealed by scanning tunneling microscopy (STM). In contrast, coupling on bare Au(111) surfaces results in less regular networks due to the simultaneous expression of competing intermolecular binding motifs in the absence of error correction. The carbon-Au-carbon bonds confer remarkable robustness to the organogold networks, as evidenced by their high thermal stability. In addition, as suggested by density functional theory (DFT) calculations and underscored by scanning tunneling spectroscopy (STS), the organogold networks exhibit a small electronic band gap in the order of 1.0 eV due to their high π-conjugation.

Sulfide-Bridged Covalent Quinoxaline Frameworks for Lithium-Organosulfide Batteries.

The chelating ability of quinoxaline cores and the redox activity of organosulfide bridges in layered covalent organic frameworks (COFs) offer dual active sites for reversible lithium (Li)-storage. The designed COFs combining these properties feature disulfide and polysulfide-bridged networks showcasing an intriguing Li-storage mechanism, which can be considered as a lithium-organosulfide (Li-OrS) battery. The experimental-computational elucidation of three quinoxaline COFs containing systematically enhanced sulfur atoms in sulfide bridging demonstrates fast kinetics during Li interactions with the quinoxaline core. Meanwhile, bilateral covalent bonding of sulfide bridges to the quinoxaline core enables a redox-mediated reversible cleavage of the sulfursulfur bond and the formation of covalently anchored lithium-sulfide chains or clusters during Li-interactions, accompanied by a marked reduction of Li-polysulfide (Li-PS) dissolution into the electrolyte, a frequent drawback of lithium-sulfur (Li-S) batteries. The electrochemical behavior of model compounds mimicking the sulfide linkages of the COFs and operando Raman studies on the framework structure unravels the reversibility of the profound Li-ion-organosulfide interactions. Thus, integrating redox-active organic-framework materials with covalently anchored sulfides enables a stable Li-OrS battery mechanism which shows benefits over a typical Li-S battery.

Vinylene-Linked 2D Conjugated Covalent Organic Frameworks by Wittig Reactions.

Vinylene-linked two-dimensional covalent organic frameworks (V-2D-COFs) have shown great promise in electronics and optoelectronics. However, only a few reactions for V-2D-COFs have been developed hitherto. Besides the kinetically low reversibility of C=C bond formation, another underlying issue facing the synthesis of V-2D-COFs is the attainment of high (E)-alkene selectivity to ensure the appropriate symmetry of 2D frameworks. Here, we tailor the E/Z selectivity of the Wittig reaction by employing a proper catalyst (i.e., Cs2 CO3 ) to obtain more stable intermediates and elevating the temperature across the reaction barrier. Subsequently, the Wittig reaction is innovatively utilized for the synthesis of four crystalline V-2D-COFs by combining aldehydes and ylides. Importantly, the efficient conjugation and decent crystallinity of the resultant V-2D-COFs are demonstrated by their high charge carrier mobilities over 10 cm2  V-1 s-1 , as revealed by non-contact terahertz (THz) spectroscopy.

Combination of Knoevenagel Polycondensation and Water-Assisted Dynamic Michael-Addition-Elimination for the Synthesis of Vinylene-Linked 2D Covalent Organic Frameworks.

Vinylene-linked two-dimensional conjugated covalent organic frameworks (V-2D-COFs), belonging to the class of two-dimensional conjugated polymers, have attracted increasing attention due to their extended π-conjugation over the 2D backbones associated with high chemical stability. The Knoevenagel polycondensation has been demonstrated as a robust synthetic method to provide cyano (CN)-substituted V-2D-COFs with unique optoelectronic, magnetic, and redox properties. Despite the successful synthesis, it remains elusive for the relevant polymerization mechanism, which leads to relatively low crystallinity and poor reproducibility. In this work, we demonstrate the novel synthesis of CN-substituted V-2D-COFs via the combination of Knoevenagel polycondensation and water-assisted dynamic Michael-addition-elimination, abbreviated as KMAE polymerization. The existence of C=C bond exchange between two diphenylacrylonitriles (M1 and M6) is firstly confirmed via in situ high-temperature NMR spectroscopy study of model reactions. Notably, the intermediate M4 synthesized via Michael-addition can proceed the Michael-elimination quantitatively, leading to an efficient C=C bond exchange, unambiguously confirming the dynamic nature of Michael-addition-elimination. Furthermore, the addition of water can significantly promote the reaction rate of Michael-addition-elimination for highly efficient C=C bond exchange within 5 mins. As a result, the KMAE polymerization provides a highly efficient strategy for the synthesis of CN-substituted V-2D-COFs with high crystallinity, as demonstrated by four examples of V-2D-COF-TFPB-PDAN, V-2D-COF-TFPT-PDAN, V-2D-COF-TFPB-BDAN, and V-2D-COF-HATN-BDAN, based on the simulated and experimental powder X-ray diffraction (PXRD) patterns as well as N2 -adsorption-desorption measurements. Moreover, high-resolution transmission electron microscopy (HR-TEM) analysis shows crystalline domain sizes ranging from 20 to 100 nm for the newly synthesized V-2D-COFs.

Control of Crystallinity of Vinylene-Linked Two-Dimensional Conjugated Polymers by Rational Monomer Design.

The interest in two-dimensional conjugated polymers (2D CPs) has increased significantly in recent years. In particular, vinylene-linked 2D CPs with fully in-plane sp2 -carbon-conjugated structures, high thermal and chemical stability, have become the focus of attention. Although the Horner-Wadsworth-Emmons (HWE) reaction has been recently demonstrated in synthesizing vinylene-linked 2D CPs, it remains largely unexplored due to the challenge in synthesis. In this work, we reveal the control of crystallinity of 2D CPs during the solvothermal synthesis of 2D-poly(phenylene-quinoxaline-vinylene)s (2D-PPQVs) and 2D-poly(phenylene-vinylene)s through the HWE polycondensation. The employment of fluorinated phosphonates and rigid aldehyde building blocks is demonstrated as crucial factors in enhancing the crystallinity of the obtained 2D CPs. Density functional theory (DFT) calculations reveal the critical role of the fluorinated phosphonate in enhancing the reversibility of the (semi)reversible C-C single bond formation.

Thiophene-Based Conjugated Acetylenic Polymers with Dual Active Sites for Efficient Co-Catalyst-Free Photoelectrochemical Water Reduction in Alkaline Medium.

Although being attractive materials for photoelectrochemical hydrogen evolution reaction (PEC HER) under neutral or acidic conditions, conjugated polymers still show poor PEC HER performance in alkaline medium due to the lack of water dissociation sites. Herein, we demonstrate that tailoring the polymer skeleton from poly(diethynylthieno[3,2-b]thiophene) (pDET) to poly(2,6-diethynylbenzo[1,2-b:4,5-b']dithiophene (pBDT) and poly(diethynyldithieno[3,2-b:2',3'-d]thiophene) (pDTT) in conjugated acetylenic polymers (CAPs) introduces highly efficient active sites for water dissociation. As a result, pDTT and pBDT, grown on Cu substrate, demonstrate benchmark photocurrent densities of 170 µA cm-2 and 120 µA cm-2 (at 0.3 V vs. RHE; pH 13), which are 4.2 and 3 times higher than that of pDET, respectively. Moreover, by combining DFT calculations and electrochemical operando resonance Raman spectroscopy, we propose that the electron-enriched Cß of the outer thiophene rings of pDTT are the water dissociation active sites, while the -C≡C- bonds function as the active sites for hydrogen evolution.

Synthesis of Vinylene-Linked Two-Dimensional Conjugated Polymers via the Horner-Wadsworth-Emmons Reaction.

In this work, we demonstrate the first synthesis of vinylene-linked 2D CPs, namely, 2D poly(phenylenequinoxalinevinylene)s 2D-PPQV1 and 2D-PPQV2, via the Horner-Wadsworth-Emmons (HWE) reaction of C2 -symmetric 1,4-bis(diethylphosphonomethyl)benzene or 4,4'-bis(diethylphosphonomethyl)biphenyl with C3 -symmetric 2,3,8,9,14,15-hexa(4-formylphenyl)diquinoxalino[2,3-a:2',3'-c]phenazine as monomers. Density functional theory (DFT) simulations unveil the crucial role of the initial reversible C-C single bond formation for the synthesis of crystalline 2D CPs. Powder X-ray diffraction (PXRD) studies and nitrogen adsorption-desorption measurements demonstrate the formation of proclaimed crystalline, dual-pore structures with surface areas of up to 440 m2 g-1 . More importantly, the optoelectronic properties of the obtained 2D-PPQV1 (Eg =2.2 eV) and 2D-PPQV2 (Eg =2.2 eV) are compared with those of cyano-vinylene-linked 2D-CN-PPQV1 (Eg =2.4 eV) produced by the Knoevenagel reaction and imine-linked 2D COF analog (2D-C=N-PPQV1, Eg =2.3 eV), unambiguously proving the superior conjugation of the vinylene-linked 2D CPs using the HWE reaction.

Aromatic Phosphonates: A Novel Group of Emitters Showing Blue Ultralong Room Temperature Phosphorescence.

In recent years, there has been a growing interest in purely organic materials showing ultralong room-temperature phosphorescence with lifetimes in the range of seconds. Still, the longest known phosphorescence lifetimes are only achieved with crystalline systems so far. Here, a rational design of a completely new family of halogen-free organic luminescent derivatives in amorphous matrices, displaying both conventional fluorescence and phosphorescence is reported. Hydrogen bonding between the newly developed emitters and an ethylene-vinyl alcohol copolymer (Exceval) matrix, which efficiently suppresses vibrational dissipation, enables bright long-lived phosphorescence with lifetimes up to 2.6 s at around 480 nm. The importance of the chosen matrix is shown as well as the implementation in an organic programmable luminescent tag.

Biobased chiral semi-crystalline or amorphous high-performance polyamides and their scalable stereoselective synthesis.

The use of renewable feedstock is one of the twelve key principles of sustainable chemistry. Unfortunately, bio-based compounds often suffer from high production cost and low performance. To fully tap the potential of natural compounds it is important to utilize their functionalities that could make them superior compared to fossil-based resources. Here we show the conversion of (+)-3-carene, a by-product of the cellulose industry into ε-lactams from which polyamides. The lactams are selectively prepared in two diastereomeric configurations, leading to semi-crystalline or amorphous, transparent polymers that can compete with the thermal properties of commercial high-performance polyamides. Copolyamides with caprolactam and laurolactam exhibit an increased glass transition and amorphicity compared to the homopolyamides, potentially broadening the scope of standard polyamides. A four-step one-vessel monomer synthesis, applying chemo-enzymatic catalysis for the initial oxidation step, is established. The great potential of the polyamides is outlined.

New Bio-Polyamides from Terpenes: α-Pinene and (+)-3-Carene as Valuable Resources for Lactam Production.

The synthesis and polymerization of two ß-lactams and two ε-lactams derived from the terpenes α-pinene and (+)-3-carene are reported. The new biopolymers can be considered as polyamide 2 (PA2) and polyamide 6 (PA6)-types with aliphatic stereoregular side chains, which lead to remarkable new properties. The macromolecules are investigated by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and infrared (IR). The (+)-3-carene-derived PA6-type is of particular interest, since it reaches a molecular weight of over 30 kDa, which is the highest value for lactam-based polyamides derived from terpenes reported to date. Additionally, a glass transition temperature (Tg ) of 120 °C is observed, surpassing the glass transition temperature of PA6 by 60 °C. The absence of a melting point (Tm ) indicates high amorphicity, another novelty for terpene-based polyamides, which might give transparent bio-polyamides access to new fields of application.