Dual-Response Photofunctional Covalent Organic Framework for Acid Detection in Various Solutions

The detection of acid in different solution environments plays a significant role in chemical, environmental and biological fields. However, reducing the constraints of detecting environment, such as aqueous, organic solvents and mixed phases of aqueous and organic phases, remains a challenge. Herein, by combining N, N, N ', N '-tetrakis(4-aminophenyl)-1,4-phenylenediamine (TPBD) and terephthalaldehyde (TA) via Shiff-base condensation, we constructed a covalent organic framework (COF) TPBD-TA COF. The COF exhibits color change from red to dark red as well as fluorescence quenching with the increase of acid contents in either aqueous or organic solvents, or a mixture of aqueous and organic solvents, due to the weak donor-acceptor interactions within the COF as well as the weak proton ionization ability of the solutions. Therefore, regardless of the detection environment, TPBD-TA COF can realize color and fluorescence dual-response to acid with the detection limit as low as 0.4 mu mol/L and 58 nmol/L, respectively, due to the protonation of the nitrogen atoms on imine bonds of the COF.

Automated summary

The detection of acid in different solution environments is crucial in chemical, environmental, and biological fields. However, the challenge lies in detecting acid in various environments such as aqueous, organic solvents, and their mixtures. To address this, a covalent organic framework (COF) called TPBD-TA COF was created by combining TPBD and TA. This COF exhibited color change and fluorescence quenching in response to increasing acid contents, regardless of the detection environment. The detection limit for acid using TPBD-TA COF was found to be 0.4 μmol/L and 58 nmol/L, respectively.