Excited -state hydrogen bonding: Detecting ammonia using an HHTP-DPB covalent organic framework

The hydrogen bonding between ammonia (NH3) and a two-dimensional material 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP)-4,4′-diphenyl-butadiynebis (boronic acid) (DPB) covalent organic framework (HHTP-DPB COF) in its electronically excited state was investigated using density functional theory and time-dependent density functional theory. The formation of the hydrogen bonding changed the luminescence mechanism of the material, which was confirmed by analysis of the frontier molecular orbitals and the corresponding electronic configurations. The comparison of the properties of hydrogen bonds in the ground state (S0) and excited state (S1) revealed that in the S1 state the hydrogen bonds were strengthened, which was adverse to the radiation transition process, and resulting in the weakening of the fluorescence intensity. After the introduction of NH3, the fluorescence rate constant of the COF was decreased and the internal conversion rate constant was increased. Therefore, these findings indicated that HHTP-DPB COF has great application prospects for detecting the indoor air pollutant NH3. © 2020