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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 influence of oxygen molecule on the luminescent properties of a cyclometalated Pt(II) complex Lxp1, was investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. Analysis of frontier molecular orbitals and electronic configuration indicated that the highest-occupied molecular orbital of the Lxp1 has a significant mixture of metal Pt (d) as well as 2-phenylpyridine and acetyl acetone( π ). The lowest-unoccupied orbital of the Lxp1 primarily locates on π * of 2-phenylpyridineligands. The emission mechanism of the cyclometalated Pt(II) complex Lxp1 is assigned to the mixing of ligand-to-metal charge transfer and ligand-to-ligand charge transfer. The emission mechanism of the Lxp1–O 2 complex can be attributed to the charge transfer from the oxygen molecule to the luminescent material Lxp1. Our study showed that intermolecular hydrogen bonding between the Lxp1 and oxygen molecule was strengthened by the calculation of electronic excitation, leading to a luminescence-decreasing phenomenon. The calculation of the radiative and non-radiative decay rate constants of the Lxp1 and the Lxp1–O 2 complex demonstrates that the phosphorescence from T 1 -S 0 of the Lxp1 would alter to the internal conversion from T 1 -T 0 of the Lxp1–O 2 complex. This alteration further explains the luminescence quenching phenomenon of the cyclometalated Pt(II) complex Lxp1 after interacting with oxygen molecule. [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]

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.The luminescence of the Covalent Organic Framework can be greatly weakened after the addition of formaldehyde. [ABSTRACT FROM AUTHOR]