Porosity Enhancement of Carbazolic Porous Organic Frameworks Using Dendritic Building Blocks for Gas Storage and Separation

We report a facile synthesis of carbazolic porous organic frameworks (Cz-POFs) via FeCl₃ promoted oxidative polymerization. Using bulky, dendritic building blocks with high connectivity, the porosity of Cz-POFs was significantly enhanced. Specifically, Cz-POF-1 and Cz-POF-3 show high surface areas of 2065 and 1927 m² g^–1, respectively. These surface areas are 3.1 and 2.1 times larger than those of Cz-POF-2 and Cz-POF-4 constructed from less branched building blocks, respectively. At 1 bar and 273 K, Cz-POF-3 exhibits the highest CO₂ uptake (21.0 wt %) and CH₄ uptake (2.54 wt %), while Cz-POF-1 has the highest H₂ uptake (2.24 wt %) at 77 K. These values are among the highest reported for porous organic polymers. In addition, Cz-POFs exhibit good ideal CO₂/N₂ selectivities (19–37) and CO₂/CH₄ selectivities (4.4–7.1) at 273 K, showing great promise for gas storage and separation applications

Fine Tuning the Redox Potentials of Carbazolic Porous Organic Frameworks for Visible-Light Photoredox Catalytic Degradation of Lignin <i>β-</i>O‑4 Models

We report a facile approach to fine tune the redox potentials of π-conjugated porous organic frameworks (POFs) by copolymerizing carbazolic electron donor (D) and electron acceptor (A) based comonomers at different ratios. The resulting carbazolic copolymers (CzCPs) exhibit a wide range of redox potentials that are comparable to common transition-metal complexes and are used in the stepwise photocatalytic degradation of lignin β-O-4 models. With the strongest oxidative capability, CzCP100 (D:A = 0:100) exhibits the highest efficiency for the oxidation of benzylic β-O-4 alcohols, while the highly reductive CzCP33 (D:A = 66:33) gives the highest yield for the reductive cleavage of β-O-4 ketones. CzCPs also exhibit excellent stability and recyclability and represent a class of promising heterogeneous photocatalysts for the production of fine chemicals from sustainable lignocellulosic biomass

“π-Hole−π” Interaction Promoted Photocatalytic Hydrodefluorination via Inner-Sphere Electron Transfer

We describe a metal-free, photocatalytic hydrodefluorination (HDF) of polyfluoroarenes (FA) using pyrene-based photocatalysts (Py). The weak “π-hole−π” interaction between Py and FA promotes the electron transfer against unfavorable energetics (Δ<i>G</i>_ET up to 0.63 eV) and initiates the subsequent HDF. The steric hindrance of Py and FA largely dictates the HDF reaction rate, pointing to an inner-sphere electron transfer pathway. This work highlights the importance of the size and shape of the photocatalyst and the substrate in controlling the electron transfer mechanism and rates as well as the overall photocatalytic processes

Ultrafast Kinetic DNA Hybridization Assay Based on the Visualization of Threshold Turbidity

We report herein the development of an ultrafast kinetic DNA hybridization assay system based on the visualization of threshold turbidity associated with the assembly of polystyrene nanospheres. Initial testing of our diagnostic protocol on a sequence associated with the anthrax lethal factor indicates that a visually identifiable, turbidity-definitive, and kinetic threshold state could be reached at a time as short as 1 min. The assay scheme allows for both target concentration quantification and differentiation of single base mismatches through registry of the threshold turbidity onset time. The positively charged environment on nanospheres not only contributes to expedited signal generation but also imparts cooperative DNA binding properties. The kinetic visual protocol complements conventionally used thermodynamic strategies and provides an entry point for the circumvention of assay issues associated with ill-defined thermodynamic end points