Synthesis and Acid-Responsive Properties of a Highly Porous Vinylene-Linked Covalent Organic Framework

Abstract

The recently emerging vinylene-linked covalent organic frameworks (VCOFs) stand out from other COFs with exceptional chemical stability and favorable light-emitting properties, promising sensing applications for acids/bases or in strong acidic/basic conditions. Here we systematically investigated the reversible color and fluorescent response of a VCOF functionalized with pyridyl groups to acids/pH. The COF was synthesized with a record surface area for VCOFs and shows reversible hydrochromic and acidochromic behaviors and concomitant fluorescence quenching. The mechanisms were probed with systematical experimental comparison with relevant COFs and model molecules in combination with orbital analysis. The response is related to significant electronic changes in the ground and photoexcited states as a result of protonation or hydrogen bonding at pyridyl sites. The COF in aqueous dispersion displays a reversible fluorescence transition with pH change, which follows the Hill equation for multisite protonation. The COF-modified test paper shows immediate and remarkable color change and fluorescence turn-off/on when alternately exposed to HCl and NH3 gases. The work illustrates the great potential of developing highly robust sensory COFs through the vinylene approach.

Enhanced surface area and reduced pore collapse of methylated, imine-linked covalent organic frameworks

“… 8 Several studies report on COF-based chemosensors for the detection of gaseous hydrochloric acid, 25,26 and a series of aqueous Brønsted acids. 26,27 Recently, Yang et al have studied the effect of imine-protonation on the optical properties of three imine-linked COFs. It was found that all COFs showed a bathochromic shift after acid exposure due to the protonation of the imine bond.…”

A cobalt covalent organic framework: a dual-functional atomic-level catalyst for visible-light-driven C–H annulation of amides with alkynes

“…Accordingly, to achieve ideal metallaphotoredox catalytic activities, [2,2′-bipyridine]-5,5′-dicarbaldehyde, possessing two suitable metal coordination sites and long π conjugated 4,4′,4′′,4′′′-(1,9-dihydropyrene-1,3,6,8-tetrayl)tetraaniline were chosen to assemble the organic backbone of the MCOF. Although similar frameworks 20 have previously been reported, and several pioneering studies on utilizing them to coordinate transition metals for classical cross couplings 21 have been developed, the introduction of cobalt onto it towards uncovering new photo reactivities for visible-light-driven C–H annulation is still the first attempt.…”

Recent trends in fluorescent aptasensors for mycotoxin detection in food: Principles, constituted elements, types, and applications

“…Others such as OTA‐intrinsic fluorescence and fluorescent polymer dots in Table 3 are not specifically described herein because these fluorescent probes are rarely used in mycotoxin fluorescent aptasensors. In addition, metal–organic frameworks (MOFs) and covalent–organic frameworks (COFs) show outstanding fluorescent properties, which can be used as fluorescent probes for sensing (Bu et al., 2021; Yang et al., 2021). However, there are few reports of applying MOFs or COFs as fluorescent probes to prepare fluorescent aptasensors for mycotoxin detection.…”