Tuning UV Absorption in Imine-Linked Covalent Organic Frameworks via Methylation

Abstract

Covalent organic frameworks (COFs) are porous materials with high surface areas, making them interesting for a large variety of applications including energy storage, gas separation, photocatalysis, and chemical sensing. Structural variation plays an important role in tuning COF properties. Next to the type of the building block core, bonding directionality, and linking chemistry, substitution of building blocks provides another level of synthetic control. Thorough characterization and comparison of various substitution patterns is relevant for the molecular engineering of COFs via rational design. To this end, we have systematically synthesized and characterized multiple combinations of several methylated and non-methylated building blocks to obtain a series of imine-based COFs. This includes the experimental assignment of the COF structure by solid-state NMR. By comparing the properties of all COFs, the following trends were found: (1) upon methylation of the aldehyde nodes, COFs show increased Brunauer−Emmett−Teller surface areas, reduced pore collapse, blue-shifted absorbance spectra, and ∼0.2 eV increases in their optical band gaps. (2) COFs with dimethylated amine linkers show a lower porosity. (3) In tetramethylated amine linkers, the COF porosity even further decreases, the absorbance spectra are clearly red-shifted, and smaller optical band gaps are obtained. Our study shows that methyl substitution patterns on COF building blocks are a handle to control the UV absorbance of the resulting frameworks.

Imine-Linked 2D Conjugated Porous Organic Polymer Films for Tunable Acid Vapor Sensing

“…FTIR spectra showed the condensation between amine and aldehyde starting materials to form imine-linked 2D-C-POPs, from the attenuated aldehyde peak at 1684 cm –1 , and the formation of the imine bond at 1618–1620 cm –1 (Figures a and S5–S8). − The attenuated presence of the CO group can be attributed to the unreacted side groups or edge groups on the peripheral boundaries of the polymeric sheets, which has been commonly observed in many previous COF materials. − To further probe the linkage chemistries, Raman spectra were obtained on the POP films and their corresponding monomers (Figures S9 and S10). Based on the comparative Raman analysis, we can conclude the absence of any considerable amount of unreacted aldehyde monomers in the POP films, evinced by the absence of CO stretching modes (1688–1700 cm –1 ), as compared to the TP monomer (Figure S9).…”

Aromatic Amine-Functionalized Covalent Organic Frameworks (COFs) for CO2/N2 Separation

“…The spectrum of the newly obtained Me 3 TFB-(NH 2 ) 2 BD sample as well as its CP build-up curve were measured (Figures S10–S12). In comparison with spectra of the small model compound 2-phenylbenzimidazole (Figures S13–S15) and Me 3 TFB-BD, the linkage was found to consist of imine bonds (Figure ). In more detail, the chemical shift of the benzimidazole carbon is at 152 ppm and the shift of the imine carbon at 162 ppm (Figure A).…”

Porphyrin–anthracene covalent organic frameworks for sustainable photosterilization

“…To endow the material with good photothermal and sustained photodynamic properties, the photosensitive unit TAPP and the chemical source of 1 O 2 DPA were selected as monomers, and the required Por-DPA was constructed by the Schiff base reaction. The highly ordered crystal structure is beneficial to the transport of oxygen and the resulting 1 O 2 , 37–39 so the key factors affecting the formation of the COF, such as the reaction solvent, reaction time and reaction temperature, were optimized in detail (Fig. S1, ESI†).…”

“…To endow the material with good photothermal and sustained photodynamic properties, the photosensitive unit TAPP and the chemical source of 1 O 2 DPA were selected as monomers, and the required Por-DPA was constructed by the Schiff base reaction. The highly ordered crystal structure is beneficial to the transport of oxygen and the resulting 1 O 2 ,[37][38][39] so the key factors affecting the formation of the COF, such as the reaction solvent, reaction time and reaction temperature, were optimized in detail (Fig.S1, ESI †). As a result, the Por-DPA COF was obtained from TAPP and DPA in a mixture solution of mesitylene/n-butanol (9/1, v/v, 2.0 mL) with 6 mol L À1 aqueous acetic acid (0.2 mL) as the catalyst at 120 1C for 3 d. The as-prepared Por-DPA exhibits good photothermal and photodynamic activities under irradiation due to the existence of the TAPP unit and high crystal structure.…”