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The interaction between a luminescent covalent organic framework (COF) and the indoor pollutant NH3 was investigated based on density functional theory and time-dependent density functional theory. The frontier molecular orbitals and electronic configuration showed that the luminescence mechanism of the COF was strongly affected by the hydrogen bond between the COF and NH3. In addition, the calculated hydrogen bond length, infrared (IR) spectra, and proton nuclear magnetic resonance (1H NMR) spectroscopy analysis indicated that the hydrogen bond in the S1 state was enhanced, which is identical to the calculated results of electronic excitation energies. The fluorescence rate coefficient of the COF was reduced when interacting with NH3. The hydrogen bond between the COF and NH3 in the S1 state is critical for the COF luminescence properties, which means that the COF shows potential application in the detection of NH3. [ABSTRACT FROM AUTHOR]

The interaction between a luminescent covalent organic framework (COF) and the indoor pollutant NH3 was investigated based on density functional theory and time-dependent density functional theory. The frontier molecular orbitals and electronic configuration showed that the luminescence mechanism of the COF was strongly affected by the hydrogen bond between the COF and NH3. In addition, the calculated hydrogen bond length, infrared (IR) spectra, and proton nuclear magnetic resonance (1H NMR) spectroscopy analysis indicated that the hydrogen bond in the S1 state was enhanced, which is identical to the calculated results of electronic excitation energies. The fluorescence rate coefficient of the COF was reduced when interacting with NH3. The hydrogen bond between the COF and NH3 in the S1 state is critical for the COF luminescence properties, which means that the COF shows potential application in the detection of NH3. [ABSTRACT FROM AUTHOR]

This article presents a recognition mechanism for nitro-explosives by the luminescent metal-organic framework 1 (LMOF-1) with the aid of density functional theory (DFT) and time-dependent density functional theory (TDDFT). The behavior of hydrogen bonding between the LMOF-1 and nitro-explosives in the S 1 state is closely associated with the fluorescence properties of the LMOF-1. In our research, we calculated the geometric configuration, 1 H NMR and IR spectra of the Complex 2 formed by LMOF-1 and nitrobenzene in the S 0 and S 1 states. The results showed that the hydrogen bond in the S 1 state was increased, which was unfavorable for the luminescence of LMOF-1. Furthermore, the fluorescence rate of LMOF-1 decreased after encapsulating nitrobenzene into it. These calculated results collectively suggest that LMOF-1 is a potential fluorescence sensor for the detection of nitro-explosives. This research was aiming to provide a better understanding of the recognition mechanism by LMOFs for nitro-explosives. [ABSTRACT FROM AUTHOR]

The fluorescence quenching mechanism of the HPHN-CQDs in the presence of Cu2+ ions. • HPHN-CQDs are prepared using pure HPHN with known molecular and crystal structures. • HPHN-CQDs exhibit an excellent luminescent recognition toward Cu2+ ions with a detection limit of 4.8 nM. • The orbital interaction diagram indicated that the presence of Cu2+ can affect the luminescence behavior of HPHN. • The electron is transferred from the excited HPHN to the 3d orbital of Cu2+. • The fluorescence rate constant of HPHN-Cu2+ was substantially decreased compared with that of HPHN. A combination of experimental and computational methods was used to study the Cu2+ ions recognition by 9-hydroxyphenal-1-one carbon quantum dots (HPHN-CQDs). HPHN-CQDs were proved to be an efficient fluorescent probe that can detect Cu2+ ions with high selectivity and sensitivity, and the detection limit was 4.8 nM. We performed a detailed analysis of the fluorescence quenching mechanism of HPHN-CQDs by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT). The orbital interaction diagram indicated that the presence of Cu2+ can affect the luminescence behavior of HPHN by changing its orbital distribution. In addition, the electron was transferred from the excited HPHN to the 3d orbital of Cu2+, which would hinder the recombination of electron-hole pairs and promote the fluorescence quenching of HPHN-CQDs. The photophysical process revealed that the fluorescence rate constant of HPHN-Cu2+ was substantially decreased compared with that of HPHN, which is consistent with the experimental results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]