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A Schiff base compound 6-amino-5-(((2-hydroxynaphthalen-1-yl)methylene)amino)-2-mercaptopyrimidin-4-ol (AHM) in acetonitrile solvent is found to show "OFF–ON type" mode upon addition of Al3+ ion and successfully applied for selective recognition of Al3+ ion. In this work, the reconsideration of excited state intramolecular proton transfer (ESIPT) and twisted intramolecular charge transfer (TICT) has been explored in detail based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. In the absence of Al3+, the lone pair electrons are transferred from –C = N to –OH forming a hydrogen-bonding configuration, and AHM shows weak fluorescence. When AHM is coordinated with metal ion, the TICT state is eliminated, and emission is significantly enhanced. Thus, in this paper, the origination of the non-emissive behavior of AHM has been explained in detail. The frontier molecular orbitals (MOs) and hole-electrons are used to analyze the charge distribution, providing strong evidence for the possibility of ESIPT and TICT processes occurring. [ABSTRACT FROM AUTHOR]

Understanding the internal mechanism of CO2 adsorption and separation of COF adsorbent materials is of great significance for high-efficiency carbon capture and storage (CCS). Herein, polyarylether-based covalent organic frameworks (PAE-COFs) structures with functionalized –CN, –COOH, and –C(NH2)NOH groups were evaluated for CO2 adsorption and separation over N2 by using grand canonical Monte Carlo (GCMC) simulation and density functional theory (DFT). Our calculation results showed that the adsorption and separation performance of CO2 in COF frameworks was related to the physical characteristics of pores, the types of gas molecules, and the interaction between COFs and gas molecules. JUC-505 modified by –CN functional group provided a feasible microporous environment with moderate specific surface area and porosity, presenting a high CO2 adsorption capacity of 5.14 mmol/g at 273 K and 1 bar. The PAE-COFs structures had good CO2/N2 separation performance, in which the CO2/N2 selectivity of JUC-505-COOH reached up to 90 at 273 K and 1 bar. Interactions analysis showed that the van der Waals and Coulomb interactions between CO2 and the framework were significantly stronger than those between N2 and the framework. Therefore, CO2 had a higher adsorption heat, which led to the larger adsorption capacity and the high selectivity of CO2 over N2. The gas radial distribution functions and 2D density distribution displayed that the CO2 adsorption corresponded to a multi-layer adsorption in frameworks, leading to the high performances of PAE-COFs for CO2 capture and separation. [ABSTRACT FROM AUTHOR]