Minimalist Design for Solar Energy Conversion: Revamping the π-Grid of an Organic Framework into Open-Shell Superabsorbers

Abstract

We apply a versatile reaction to a versatile solid: the former involves the electron-deficient alkene tetracyanoethylene (TCNE) as the guest reactant; the latter consists of stacked 2D honeycomb covalent networks based on the electron-rich βketoenamine hinges that also activate the conjugated, connecting alkyne units. The TCNE/alkyne reaction is a [2 + 2] cycloaddition−retroelectrocyclization (CA-RE) that forms strong push− pull units directly into the backbone of the framework�i.e., using only the minimalist "bare-bones" scaffold, without the need for additional side groups of alkynes or other functions. The ability of the stacked alkyne units (i.e., as part of the honeycomb mass) to undergo such extensive rearrangement highlights the structural flexibility of these covalent organic framework (COF) hosts. The COF solids remain porous, crystalline, and air-/water-stable after the CA-RE modification, while the resulting push−pull units feature distinct open-shell/free-radical character, are strongly light-absorbing, and shift the absorption ends from 590 nm to around 1900 nm (band gaps from 2.17−2.23 to 0.87−0.95 eV), so as to better capture sunlight (especially the infrared region which takes up 52% of the solar energy). As a result, the modified COF materials achieve the highest photothermal conversion performances, holding promise in thermoelectric power generation and solar steam generation (e.g., with solar-vapor conversion efficiencies >96%).

Regulating the Tautomerization in Covalent Organic Frameworks for Efficient Sacrificial Agent-Free Photocatalytic H2O2 Production

“…Both COFs possessed sufficient driving force for the 2e – ORR toward H 2 O 2 production based on thermodynamic consideration. As shown in the photoluminescence (PL) spectrum (Figure S15a), while DHAA-Tp COF exhibited fluorescence intensities, TCNAQ-Tp COF showed nonemissive under the light excitation at 400 nm, which was probably caused by nonradiative transition . We further investigated the behavior of excitons by time-resolved fluorescence decay.…”

Easy but Efficient: Facile Approach to Molecule with Theoretically Justified Donor–Acceptor Structure for Effective Photothermal Conversion and Intravenous Photothermal Therapy

“…[ 24 ] Very recently, He et al reported facile modification of the main skeleton of alkynes on COF to give a framework holding persistent radicals for high PCE together with solar‐vapor conversion efficiencies > 96%. [ 25 ] However, there are few studies on the application of D–A structured motifs prepared from CA–RE reactions for photothermal conversion while most of the studies focus on non‐linear optics and photoluminescent materials. [ 26 ] Even though the aforementioned COFs bearing D–A junctions have been adopted for photothermal conversion, these COFs are not nanoscale or insoluble to be utilized for PTT.…”