Computational insights into the mechanism of formaldehyde detection by luminescent covalent organic framework

Luminescent covalent organic frameworks (COFs) as fluorescent sensor materials provide a distinct advantage over other materials. In this work, we investigated the hydrogen bonding between the luminescent COF Ph-An-COF and formaldehyde in its excited electronic state by using density functional theory and time-dependent density functional theory to determine whether this type of COF can be used for formaldehyde detection. Hydrogen bonding significantly changed the nature of the frontier orbital and the luminescent properties. Our study reveals that the hydrogen bonding was strengthened in the excited state and the fluorescence rate coefficient was significantly reduced, which is not favorable for the luminescence of this type of COF and would lead to a luminescence decrease or quenching phenomenon. Therefore, this type of luminescent COF can be used as a potential chemical sensor to detect formaldehyde. This work provides an insight into the design of luminescence covalent organic frameworks.