A 2D covalent organic framework as a sensor for detecting formaldehyde.

Formaldehyde is the main cause of indoor pollution. In this research, we investigated the mechanism that the covalent organic framework (COF) identifies formaldehyde applying density functional theory (DFT) and time-dependent (TD) DFT approaches. On one hand, the calculation results of the geometric parameters, IR spectra, as well as 1H-NMR chemical shifts for protons that associated with the hydrogen bonding formation together with the electronic transition energies verified that the furcate hydrogen bonding formed between the COF and formaldehyde is enhanced in the excited S1 state and it is not beneficial to luminescence of the COF. On the other hand, excitingly, our further calculation results of the fluorescence rate coefficients also revealed that the strengthened hydrogen bonding behavior in S1 state caused an efficiently weakened luminescent phenomenon compared with that of the COF. Therefore, this analysis method, which qualitative collaborates with quantitative theoretically, demonstrates the possibility that the COF could be served as a sensor to detect formaldehyde. Graphical Abstract The luminescence of the Covalent Organic Framework can be greatly weakened after the addition of formaldehyde.