Ratiometric Fluorescent pH Sensor Based on a Tunable Multivariate Covalent Organic Framework

Abstract

Ratiometric detection of pH is always significant in environmental regulation, medical diagnosis, synthetic chemistry, and beyond. The construction of practical ratiometric pH sensors with reusability is still challenging. Herein, by exploiting a multivariate strategy, we first synthesized and reported a series of novel three-component covalent organic frameworks (COF-COOH X , X = 33, 50, and 67) through Schiff base reaction between 2-hydroxybenzene-1,3,5-tricarbaldehyde (HTA), 4,4′-diamino-3,3′biphenyldicarboxylic acid (DBA), and 5,5′-diamino-2,2′-bipyridine (BPY) at various molar ratios (X = [DBA]/([BPY] + [DBA]) × 100 = 33, 50, and 67). COF-COOH X (X = 33, 50, and 67) displayed ratiometric pH sensing performance in acidic conditions with selectivity and repeatability. By tuning the molar ratio of DBA and BPY, the fluorescent properties, linear pH responsive ranges, and pK a values of COF-COOH X (X = 33, 50, and 67) can be regulated. Meanwhile, the two-component COF-COOH 0 and COF-COOH 100 did not exhibit ratiometric pH detection ability. Moreover, the constructed three ratiometric sensors can be applied to detect pH in drug solutions and carbonated drinks with satisfactory results. This work sheds new light on the design and fabrication of innovative ratiometric fluorescent sensors using COFs.

Recent advances of stimuli-responsive viologen-based nanocomposites

“…115 As mentioned above, the layered structure of COFs can be adjusted by introducing viologen groups, and the photoelectric sensing performance of COFs can be enhanced using the photoelectric activity of viologen groups. 116 Therefore, viologenbased COFs possess great potential to be applied in diverse fields, such as photoelectric catalysis, pollutant detection, biosensing, energy storage, heterogeneous catalysis, 117 pH fluorescence sensing, 118 and luminescence thermometry. 119 However, the research on viologen-based COFs is still in its infancy.…”

Tetrazine‐Linked Covalent Organic Frameworks With Acid Sensing and Photocatalytic Activity

“…[11][12][13] In particular, COFs containing reactive nitrogen or basic building blocks have demonstrated significant potential as acid sensors thanks to their ability to undergo structural variations in response to changes in pH. [14][15][16][17] COFs can be used to detect the presence of acidic gases, such as hydrochloric acid, [18] nitric oxide, [19] or nitrogen dioxide [20] in the atmosphere. The use of COFs for acid sensing offers several advantages over conventional sensing materials, including being lightweight, recyclable, and having higher sensitivity, selectivity, and durability.…”

Trifluoromethyl-Functionalized 2D Covalent Organic Framework for High-Resolution Separation of Isomers

“…Chromatographic column is the core component of GC, and introduction of novel stationary phases is vital for chromatographic separation. , Covalent organic frameworks (COFs), composed of light elements such as C, O, N, H, and B, are a class of porous materials connected by dynamic covalent bonding. COFs have drawn widespread attention for various applications in adsorption, − catalysis, , sensing, − and separation − due to their excellent features such as high stability, abundant pore channels, and large surface area . The designability of COFs endows them the potential to introduce various forces to improve selectivity as the stationary phase. − Functional groups such as hydroxyl and amino groups are usually introduced to COFs to improve the separation performance .…”