Saturated Linkers in Two-Dimensional Covalent Organic Frameworks Boost Their Luminescence

The development of highly luminescent two-dimensional covalent organic frameworks (COFs) for sensing applications remains challenging. To suppress commonly observed photoluminescence quenching of COFs, we propose a strategy involving interrupting the intralayer conjugation and interlayer interactions using cyclohexane as the linker unit. By variation of the building block structures, imine-bonded COFs with various topologies and porosities are obtained. Experimental and theoretical analyses of these COFs disclose high crystallinity and large interlayer distances, demonstrating enhanced emission with record-high photoluminescence quantum yields of up to 57% in the solid state. The resulting cyclohexane-linked COF also exhibits excellent sensing performance for the trace recognition of Fe3+ ions, explosive and toxic picric acid, and phenyl glyoxylic acid as metabolites. These findings inspire a facile and general strategy to develop highly emissive imine-bonded COFs for detecting various molecules.journal articl

Two-dimensional sp2 carbon–conjugated covalent organic frameworks

We synthesized a two-dimensional (2D) crystalline covalent organic framework (sp2c-COF) that was designed to be fully π-conjugated and constructed from all sp2-carbons by C=C condensation reactions of tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile. The C=C linkages topologically connect pyrene knots at regular intervals into a 2D lattice with π-conjugations extended along both x and y directions, and develop an eclipsed layer framework rather than the more conventionally obtained disordered structures. The sp2c-COF is a semiconductor with a discrete band gap of 1.9 eV and can be chemically oxidized to enhance conductivity by 12 orders of magnitude. The generated radicals are confined on the pyrene knots, enabling the formation of a paramagnetic carbon structure with high spin density. The sp2-carbon framework induces ferromagnetic phase transition to develop spin-spin coherence and align spins unidirectionally across the material

On-surface polyarylene synthesis by cycloaromatization of isopropyl substituents

Immobilization of organic molecules on metal surfaces and their coupling via thermally induced C–C bond formation is an important technique in organic and polymer synthesis. Using this approach, insoluble and reactive carbon nanostructures can be synthesized and the reactions monitored in situ using scanning probe microscopy methods. The diversity of conceivable products, however, is limited by the number and variety of known on-surface reactions. Here, we introduce the on-surface synthesis of polyarylenes by intermolecular oxidative coupling of isopropyl substituents of arenes. This [3+3] dimerization reaction forms a new phenylene ring and can be regarded as a formal cycloaromatization. The synthetic value of this reaction is proved by the synthesis of polyarylenes and co-polyarylenes, which we demonstrate by synthesizing poly(2,7-pyrenylene-1,4-phenylene). Scanning tunnelling microscopy and non-contact atomic force microscopy studies, complemented by density functional theory calculations, offer mechanistic insight into the on-surface cycloaromatization reaction

A Highly Luminescent Nitrogen-Doped Nanographene as an Acid- and Metal-Sensitive Fluorophore for Optical Imaging

Dibenzo[hi,st]ovalene (DBOV) has excellent photophysical properties, including strong fluorescence and high ambient stability. Moreover, the optical blinking properties of DBOV have enabled optical super-resolution single-molecule localization microscopy with an imaging resolution beyond the diffraction limit. Various organic and inorganic fluorescent probes have been developed for super-resolution imaging, but those sensitive to pH and/or metal ions have remained elusive. Here, we report a diaza-derivative of DBOV (N-DBOV), synthesized in eight steps with a total yield of 15%. Nitrogen (N)-bearing zigzag edges were formed through oxidative cyclization of amino groups in the last step. UV–vis and fluorescence spectroscopy of N-DBOV revealed its promising optical properties comparable to those of the parent DBOV, while cyclic voltammetry and density functional theory calculations highlighted its lower orbital energy levels and potential n-type semiconductor character. Notably, in contrast to that of the parent DBOV, the strong luminescence of N-DBOV is dependent on pH and the presence of heavy metal ions, indicating the potential of N-DBOV in sensing applications. N-DBOV also exhibited pH-responsive blinking, which enables pH-sensitive super-resolution imaging. Therefore, N-DBOV appears to be a highly promising candidate for fluorescence sensing in biology and environmental analytics

Designed synthesis of stable light-emitting two-dimensional sp2 carbon-conjugated covalent organic frameworks

Topological connection of organic chromophores is an attractive way to design light-emitting covalent organic frameworks but the synthesis of stable light-emitting frameworks remains challenging. Here the authors report the designed synthesis of sp2 carbon conjugated frameworks that combine stability with light-emitting activit

Highly crystalline polyimide covalent organic framework as dual-active-center cathode for high-performance lithium-ion batteries

Polyimide covalent organic framework (PI-COF) materials that can realize intrinsic redox reactions by changing the charge state of their electroactive sites are considered as emerging electrode materials for rechargeable devices. However, the highly crystalline PI-COFs with hierarchical porosity are less reported due to the rapid reaction between monomers and the poor reversibility of the polyimidization reaction. Here, we developed a water-assistant synthetic strategy to adjust the reaction rate of polyimidization, and PI-COF (COFTPDA-PMDA) with kgm topology consisting of dual active centers of N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine (TPDA) and pyromellitic dianhydride (PMDA) ligands was successfully synthesized with high crystallinity and porosity. The COFTPDA-PMDA possesses hierarchical micro-/mesoporous channels with the largest surface area (2669 m2/g) in PI-COFs, which can promote the Li+ ions and bulky bis(trifluoromethanesulfonyl)imide (TFSI-) ions in organic electrolyte to sufficiently interact with the dual active sites on COF skeleton to increase the specific capacity of cathode materials. As a cathode material for lithium-ion batteries, COFTPDA-PMDA@50%CNT which integrated high surface area and dual active center of COFTPDA-PMDA with carbon nanotubes via π-π interactions gave a high initial charge capacity of 233 mAh/g (0.5 A/g) and maintains at 80 mAh/g even at a high current density of 5.0 A/g after 1800 cycles.This work was supported by the Jilin Province Science and Technology Development Plan (20210101112JC and 20220101048JC), the National Natural Science Foundation of China (21871104, 21621001, 22288101, and 22133005), the Natural Science foundation of Shanghai (20ZR1427600), and the Opening Project of State Key Laboratory of High Performance Ceramics and Superfine Microstructure (SKL202105SIC)

9‑Arylidene‑9<i>H</i>‑Fluorene-Containing Polymers for High Efficiency Polymer Solar Cells

9-Arylidene-9<i>H</i>-fluorene containing donor–acceptor (D–A) alternating polymers <b>P1</b> and <b>P2</b> were synthsized and used for the fabrication of polymer solar cells (PSCs). High and low molecular weight <b>P1</b> (<b>HMW-P1</b> and <b>LMW-P1</b>) and high molecular weight <b>P2</b> were prepared to study the influence of molecular weight and the position of alkoxy chains on the photovoltaic performance of PSCs. <b>HMW-P1</b>:PC₇₁BM-based PSCs fabricated from 1,2-dichlorobenzene (DCB) solutions showed a power conversion efficiency (PCE) of 6.26%, while <b>LMW-P1</b>:PC₇₁BM-based PSCs showed poor photovoltaic performance with a PCE of only 2.75%. PCE of <b>HMW-P1</b>:PC₇₁BM-based PSCs was further increased to 6.52% with the addition of 1,8-diiodooctane (DIO) as the additive. Meanwhile, PCE of only 2.51% was obtained for <b>P2</b>:PC₇₁BM-based PSCs. The results indicated that the position of alkoxy substituents on the 9-arylidene-9H-fluorene unit and the molecular weight of polymers are very crucial to the photovoltaic performance of PSCs