The phenyl acetylene and benzyl azide cycloaddition reaction in water in the presence of β-cyclodextrin (β-CD) as a phase transfer catalyst (PTC) can get a better yield in a shorter time. The interaction between β-CD and phenyl acetylene or benzyl azide plays an important role in this reaction. This paper studies the complexes of β-CD with phenyl acetylene and benzyl azide using density functional theory (DFT) method. In order to find out the orientations of guests in the cavity of β-CD, binding energy and deformation energy are investigated, and the calculated results are confirmed by ¹H nuclear magnetic resonance (¹HNMR). The data from single point energy indicate that the inclusion complexes can improve the solubilities of phenyl acetylene and benzyl azide in water. The ¹³C and ¹⁵N spectra show that the most obvious variation concentrates on C₆ and C₈ of phenyl acetylene and N₁₅ of benzyl azide in complexes. Mulliken charge and frontier orbital are employed for revealing the charge distribution. The effect of β-CD is discussed in terms of the calculated parameters. Copyright © 2014 John Wiley & Sons, Ltd.

Three derivatives of alkyl anthracene covalently bonded to aza-18-crown-6 at the nitrogen position, anthracene(CH₂)_n, (n = 1–3) which act as an on–off fluorogenic photoswitch have been theoretically studied using a computational strategy based on density functional theory at B3LYP/6-31 + G(d,p) method. The fully optimized geometries have been performed with real frequencies which indicate the minima states. The binding energies, enthalpies and Gibbs free energies have been calculated for aza-18-crown-6 (L) and their metal complexes. The natural bond orbital analysis is used to explore the interaction of host–guest molecules. The absorption spectra differences between L and their metal ligands, the excitation energies and absorption wavelength for their excited states have been studied by time-dependent density functional theory with the basis set 6-31 + G(d,p). These fluorescent sensors and switchers based on photoinduced electron transfer mechanism have been investigated. The PET process from aza-crown ether to fluorophore can be suppressed or completely blocked by the entry of alkali metal cations into the aza-crown ether-based receptor. Such a suppression of the PET process means that fluorescence intensity is enhanced. The binding selectivity studies of the aza-crown ether part of L indicate that the presence of the alkali metal cations Li⁺, Na⁺ and K⁺ play an important role in determining the internal charge transfer and the fluorescence properties of the complexes. In addition, the solvent effect has been investigated. Copyright © 2014 John Wiley & Sons, Ltd.

A novel fluorescent switchable chemosensor 1, which is composed of an anthracene-modified calix[4]crown in the 1,3-alternate conformation, was calculated by density functional theory and time-dependent density functional theory method. Geometries, molecular orbitals and binding thermal energies were evaluated at the restricted hybrid Becke's three-parameter exchange functional using 6-31 G(d) basis set and relativistic effective core potentials. The metal–ligand and cation–π interactions were investigated acting as two main types of driving force. Our calculations clearly show that solvent effects strongly influence cation selectivity, and K⁺ selectivity is recovered when even a few waters of hydration are considered. The calculations indicate that because of the photoinduced electron transfer effect, the addition of alkali metal ions have hardly any effect on the fluorescence of ligand 1 under neutral or basic conditions. Also, the high selectivity of ligand 1 for K⁺ and Rb⁺, under acidic conditions, the complexed metal ion can result in ammonium ion deprotonation, which leads to quenching of fluorescence of 1•H⁺. Copyright © 2012 John Wiley & Sons, Ltd.

The binding interactions of bis-3-benzo-15-crown-5 ethers and bis-3-benzo-18-crown-6 ethers (neutral hosts) with a series of alkali metal cations Na⁺, K⁺, Rb⁺ and Cs⁺ (charged guests) were investigated using quantum chemical density functional theory. Different optimized structures, binding energies and various thermodynamic parameters of free crown ethers and their metal cation complexes were obtained based on the Becke, three-parameter, Lee–Yang–Parr functional using mixed basis set (C, H, O, Na⁺ and K⁺ using 6-31 g, and the heavier cation Rb⁺ and Cs⁺ using effective core potentials). Natural bond orbital analysis is conducted on the optimized geometric structures. The main types of driving force host–guest interactions are investigated. The electron donating O offers a lone pair of electrons to the contacting LP* (1-center valence antibond lone pair) orbitals of metal cations. The bis-3-benzocrown ethers are assumed to have sandwich-like conformations, considering the binding energies to gauge the exact interactions with alkali cations. It is found that there are two different types of complexes: one is a tight ion pair and the other is a separated ion pair. Copyright © 2011 John Wiley & Sons, Ltd.

A series of ring-contracted (14-crown-5, 17-crown-6) and ring-enlarged (16-crown-5, 17-crown-5, 19-crown-6, 20-crown-6) crown ethers and their complexes with alkali-metal cations Na⁺ and K⁺ had been explored using density functional theory (DFT) at B3LYP/6-31G* level in order to reveal the effects of the methylene-chain length in a crown ether. The nucleophilicity of all crown ethers had been investigated by the Fukui functions. The quantum chemistry parameters, such as the energy gap (ΔE), the highest occupied molecular orbital energy (E_HOMO) and the lowest unoccupied molecular orbital energy (E_LUMO) for less-symmetrical crown ethers and symmetrical frameworks (15-crown-5, 18-crown-6) had been calculated. In addition, the thermodynamic energies of complexation reactions had also been studied. The results of the DFT calculations show that the methylene-chain length plays an important role in determining the structure characters of the crown ethers and also strongly influences the properties of the ethers. Some of the calculated results are in a good agreement with the experimental values.

The polycarbazoles have been proved to efficiently suppress the keto defect emission. Three carbazole-based conjugated polymers, poly[9-methyl-3-(4-vinylstyryl)-9H-carbazole] (PBC), poly[9-methyl-3-(2-(5-vinylthiophen-2-yl)vinyl)-9H-carbazole] (PBT) and poly[9-methyl-3-(2-(5-vinylfuran-2-yl)vinyl)-9H-carbazole] (PBF), were investigated by quantum-chemical techniques, and gain a detailed understanding of the influence of carbazole units and the introduction of electron-donating on the electronic and optical properties. The electronic properties of the neutral molecules, HOMO-LUMO gaps (ΔE), in addition to ionization potential (I_p) and electron affinity (E_a), are studied using B3LYP density functional theory. The lowest excitation energies (E_g) and the absorption wavelength are studied using the time dependent density functional theory (TDDFT). The calculated results show that all three series of polymers have good planarity. And the highest-occupied molecular orbital (HOMO) energies lift about 0.36–0.61 eV and thus the I_P decrease about 0.01–0.19 eV compared to polycarbazole, suggesting the significant improved hole-accepting and transporting abilities. By introducing the electron-donating 1,4-divinylphenylene or 2,5-divinylthiophene or 2,5-divinylfuran units in the backbone, and the lowest-unoccupied molecular orbital (LUMO) energies decrease 0.20–0.39 eV. In addition, PBC, PBT and PBF have longer maximal absorption wavelengths than polycarbazole. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 706–714, 2009