Conjugated Covalent Organic Frameworks via Michael Addition–Elimination

Abstract

Dynamic covalent chemistry enables self-assembly of reactive building blocks into structurally complex yet robust materials, such as covalent organic frameworks (COFs). However, the synthetic toolbox used to prepare such materials, and thus the spectrum of attainable properties, is very limited. For π-conjugated COFs, the Schiff base condensation of aldehydes and amines is the only general dynamic reaction, but the resulting imine-linked COFs display only a moderate electron delocalization and are susceptible to hydrolysis, particularly in acidic conditions. Here we report a new dynamic polymerization based on Michael addition-elimination reaction of structurally diverse β-ketoenols with amines, and use it to prepare novel two-dimensional (2D) π-conjugated COFs, as crystalline powders and exfoliated micron-size sheets. π-Conjugation is manifested in these COFs in significantly reduced band gap (1.8-2.2 eV), solid state luminescence and reversible electrochemical doping creating midgap (NIR absorbing) polaronic states. The β-ketoenamine moiety enables protonation control of electron delocalization through the 2D COF sheets. It also gives rise to direct sensing of triacetone triperoxide (TATP) explosive through fluorescence quenching.

Opportunities of Covalent Organic Frameworks for Advanced Applications

“…[74] As a result of enhanced π-conjugation, the bandgap (1.8-2.2 eV) in the resultant COFs is significantly reduced in comparison with imine-linked COFs (0.2-0.3 eV), which also exhibit solid state luminescence and reversible electrochemical doping. [74] As a result of enhanced π-conjugation, the bandgap (1.8-2.2 eV) in the resultant COFs is significantly reduced in comparison with imine-linked COFs (0.2-0.3 eV), which also exhibit solid state luminescence and reversible electrochemical doping.…”

2D Poly(arylene vinylene) Covalent Organic Frameworks via Aldol Condensation of Trimethyltriazine

“…[7] Owing to their welldefined porosity and large active surface area, COFs have gained significant attention for applications in gas and energy storage,and catalysis. [10] While promising optoelectronic properties have been reported in some of these, [11] the highly polarized C-N links might limit the charge carrier delocalization (which marginalizes semiconducting applications of 1D conjugated polyazomethines). [10] While promising optoelectronic properties have been reported in some of these, [11] the highly polarized C-N links might limit the charge carrier delocalization (which marginalizes semiconducting applications of 1D conjugated polyazomethines).…”

Kovalente organische Gerüstverbindungen: chemische Ansätze für Designerstrukturen und integrierte Funktionen

“…[101] Aufgrund ihrer Schichtstruktur kçnnen COFs zu Nanoblättern exfoliert werden. Exfoliation kann durch zwei Verfahren erfolgen:U ltraschallbehandlung in Delaminationslçsungsmitteln [124][125][126][127] und mechanisches Mahlen. [128,129] So ergibt eine Suspension von boronatesterverknüpftem COF-8 (1 mg mL À1 )i nnerhalb von 15 min Ultraschallbehandlungi n wasserfreiem CH 2 Cl 2 Nanoblätter.…”