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Crown ether can bind the alkali metal ions, and the binding is related to numerous factors. In present work, we investigated the effect of the species and number of heteroatom on the interaction energy and charge transfer between crown ether and alkali metal ions in the three complexes (12C4O-Li+, 15C5O-Na+ and 18C6O-K+) using density functional method. Our results show that the N- or S-substitution is more favorable to the enhancement of charge transfer between the alkali metal ions and crown ethers than P-substitution; furthermore, the interaction energy of N- or S-substitution is also higher than that of P-substitution. The 12C4O has strongest affinity for Li+ in the three complexes from the perspective of the variation of the species and the number of heteroatom. Thus, take 12C4O for example, it is concluded that the number of N-substitution has slight influence on the interaction energy; however, as the number of P- or S-substitutions increases, the interaction energy values decrease sharply.

In this work, [26]hexaphyrin (1.1.1.1.1.1) and corresponding [28]hexaphyrin (1.1.1.1.1.1) with different structures have been investigated using density functional theory (DFT) and time-dependent DFT. The frontier molecular orbitals (FMOs), aromaticity, electronic spectra and nonlinear optical properties were systematically investigated. Significantly, thienyls groups on the meso -carbon have great influence on the electronic properties. Based on an analysis of orbital composition, contribution of the thienyls to FMOs concentrates primarily on HOMO and third highest occupied molecular orbital (HOMO−2) to aromatic molecules, and focuses on second highest occupied molecular orbital (HOMO−1) to antiaromatic molecules. In addition, the first hyperpolarizability ( β 0 ) values of dumbbell-shape and rectangular-shape molecules are significantly lower than those of the other three molecules. For the other three molecules with both aromatic molecules and antiaromatic molecules, their β 0 values have the same regularities that are in the orders of triangular-shape β 0 value of antiaromatic molecules is greater than that of aromatic molecules because of their different transition properties. We hope that this work will provide valuable information for adjusting electro-optical properties by changing substituent group on the meso -carbon, aromaticity and configuration.

The similar molecules [2.2]paracyclophane (22PCP) and 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane (8F22PCP) have both generated considerable synthetic interest since they were first prepared. In this work, the nonlinear optical properties of 22PCP, 8F22PCP, and the related Li-doped systems 22PCP-Li and 8F22PCP-Li (which have a Li atom above 22PCP and 8F22PCP, respectively) were investigated. An analysis of natural bond orbital charges showed that there is greater charge transfer from the Li atom to the benzene rings in 8F22PCP-Li than in 22PCP-Li. The variation in the calculated nucleus independent chemical shift (NICS) value as a function of the distance from the lower benzene ring towards the upper benzene ring was found to be W-shaped for both 22PCP and 22PCP-Li. Moreover, whereas all of the NICS values of 22PCP and 22PCP-Li were markedly negative, all of the NICS values of 8F22PCP and 8F22PCP-Li were either positive or only moderately negative. Calculations of the electro-optical properties of these systems showed that the first hyperpolarizability of 22PCP-Li was noticeably larger than that of 8F22PCP-Li. According to the two-level model, the larger first hyperpolarizability of 22PCP-Li is due to its smaller transition energy.

A series of hexaphyrins with different meso-carbon atoms and their protonated structures were investigated using density functional theory (DFT) and time-dependent DFT. Frontier molecular orbitals (FMOs), aromaticity, and electronic spectra were investigated systematically before and after protonation. The FMO energy gaps before and after protonation were different for the antiaromatic molecules, while they were only slightly different for the aromatic molecules. By analyzing the electronic spectra of the aromatic molecules, the absorption peaks in the Q-like and B-like bands were not significantly different before and after protonation. However, the absorption peaks of the antiaromatic molecules were clearly different before and after protonation in both the Q-like and B-like bands. [24]Hexaphyrin (1.0.1.0.1.0) has 24 π-electrons and is Huckel antiaromatic. However, the absorption spectrum of protonated [24]hexaphyrin (1.0.1.0.1.0) showed aromaticity. In addition, these conclusions were generally consistent with the FMOs, nucleus-independent chemical shifts, harmonic oscillator model of aromaticity, and absorption spectra. Although protonated [24]hexaphyrin (1.0.1.0.1.0) has 24 π-electrons and is Huckel antiaromatic, it has Mobius aromaticity because of the single-sided Mobius topological structure. This explains why [24]hexaphyrin (1.0.1.0.1.0) has diatropic ring currents in solvent. To the best of our knowledge, this system is the smallest Mobius aromatic molecule among the many uncoordinated extended porphyrins.