Solvatochromic covalent organic frameworks

Abstract

Covalent organic frameworks (COFs) are an emerging class of highly tuneable crystalline, porous materials. Here we report the first COFs that change their electronic structure reversibly depending on the surrounding atmosphere. These COFs can act as solid-state supramolecular solvatochromic sensors that show a strong colour change when exposed to humidity or solvent vapours, dependent on vapour concentration and solvent polarity. The excellent accessibility of the pores in vertically oriented films results in ultrafast response times below 200 ms, outperforming commercially available humidity sensors by more than an order of magnitude. Employing a solvatochromic COF film as a vapour-sensitive light filter, we demonstrate a fast humidity sensor with full reversibility and stability over at least 4000 cycles. Considering their immense chemical diversity and modular design, COFs with fine-tuned solvatochromic properties could broaden the range of possible applications for these materials in sensing and optoelectronics.

Synthesis of Two‐Dimensional Covalent Organic Frameworks in Ionic Liquids

“…The diffraction peak positions of both COFs are the same as those synthesized under solvothermal conditions. The crystalline structure of TFPPy‐PDA‐COF and TFPPy‐PyTTA‐COF has been reported to be monoclinic C 2/ m and P 2/ m space groups, respectively, which are different from those our proposed orthorhombic Cmm 2 and Pmm 2 space groups. However, our calculations indicate that the energies of both COFs in orthorhombic space group are slightly lower than those in monoclinic space group, revealing that the orthorhombic space group structure for both COFs is more stable (Supporting Information).…”

“…In this work, for the first time, we report the synthesis of two‐dimensional (2D) COFs by exploring ILs as reaction media. We demonstrated this method for the synthesis of imine‐linked 2D COFs; one is mesoporous TFPPy‐PDA‐COF by polycondensation of 1,3,6,8‐tetrakis(4‐formylphenyl)pyrene (TFPPy) with p ‐phenylenediamine (PDA), and another is microporous TFPPy‐PyTTA‐COF by condensation of TFPPy with 4,4′,4′′,4′′′‐(pyrene‐1,3,6,8‐tetrayl)tetraaniline (PyTTA) (Figure , Supporting Information). As control, these COFs were also prepared under solvothermal conditions.…”

Dual‐Function Fluorescent Covalent Organic Frameworks: HCl Sensing and Photocatalytic H2 Evolution from Water

“…These hydrogen bonds would enhance the stability of the excited states of the COFs and, thus, accelerate intramolecular charge-transfer processes-a well-established solvent relaxation phenomenon and decrease the energy required for photoexcitation. [49][50][51][52][53] We ascribe the greater red-shifting of the signal for the PyTA-BC-Ph COF relative to that of the PyTA-BC COF to the longer conjugated length in the former. The fluorescence lifetime of the PyTA-BC COF was 3.56 ns, while that of the PyTA-BC-Ph COF was 3.89 ns.…”

Solution‐Processable Carbon Nitride Polymers for Photoelectrochemical Applications

“…Moreover, we found that the optical properties of the PAH‐CNs are sensitive to the polarity of the solvent; the changes are especially prominent for NapCN, AnCN, and PyCN, with a blue shift that is more pronounced in THF than in the more polar DMSO (Figure f; Figure S24b, Supporting Information). This positive solvatochromism means that the excited state is more stabilized than the ground state due to better solvation . The solvatochromic effect in the new PAH‐CNs enables the tunability of photophysical properties of CNs, as shown in Figure d; Figure S25, Supporting Information.…”