Second-Order Nonlinear Optical Responses and Concave–Convex Interactions of Size-Selective Fullerenes/Corannulene Recognition Pairs: The Effect of Fullerene Size

The size-selective formation of eight molecular recognition pairs between the host corannulene and fullerene guest of various size have been studied by taking advantage of concave–convex π–π interactions. Herein, the structures, binding interactions, electronic absorption spectra, and first hyperpolarizabilities have been explored using density functional theory calculations. It is found that with the aim to maximize the concave–convex shape complementarity, the base of fullerene can be modified at certain angles with the central ring plane of C₂₀H₁₀ (0° for complexes <b>1</b>–<b>4</b> and 46°, 34°, 19°, and 5° for complexes <b>5</b>–<b>8</b>, respectively). The interaction energies depend linearly on the convex surface area and the size of the fullerene sphere. Further, the results of first hyperpolarizabilities show that the shape of the fullerene is the dominant factor for complexes <b>1</b>–<b>4</b> because of the intramolecular charge transfer (CT) within fullerene cage. Among them, complex <b>4</b> presents the largest β_tot value as 5.64 × 10^–30 esu because of the more obvious intramolecular CT from the upper part to the bottom part of the C₇₀ cage, derived from the larger height of the cage. On the other hand, low-lying CT character accounts for a large part of the first hyperpolarizability. The achieved understanding provides the prospect of size-selective strategy for enhancing the concave–convex interaction and second order nonlinear optical response in the recognition of fullerenes

Third-Order Nonlinear Optical Properties of Endohedral Fullerene (H₂)₂@C₇₀ and (H₂O)₂@C₇₀ Accompanied by the Prospective of Novel (HF)₂@C₇₀

In view of the experimental observation of (H₂)₂@C₇₀ and (H₂O)₂@C₇₀, it has been suggested that hydrogen fluoride (HF) dimer can be completely localized within the sub-nanospace inside the fullerene C₇₀ cage. With the aim of quantum chemical prospective of (HF)₂@C₇₀, electronic structure calculations of C₆₀ hosting H₂, HF, and H₂O monomers, as well as C₇₀ hosting H₂, HF, and H₂O monomers and dimers, were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population, and interaction energy calculation. The F–H···F bonding energy inside C₇₀ was estimated at −13.25 kcal/mol, which is smaller than that of free dimer in the gas phase (−8.37 kcal/mol). Exploration of various featured properties suggests that (HF)₂@C₇₀ may be also regarded as a unique system composed of both inter- and intramolecular interactions like (H₂)₂@C₇₀ and (H₂O)₂@C₇₀. In addition, absorption spectroscopy and linear and nonlinear optical coefficients of C₆₀ hosting H₂, HF, and H₂O monomers, as well as C₇₀ hosting H₂, HF, and H₂O monomers and dimers, have also been forecasted. The results show that there is almost no influence of embedded H₂, HF, and H₂O monomers and dimers on the peak wavelength of absorption spectra for C₆₀ and C₇₀. Endohedral C₇₀ possesses the larger second hyperpolarizabilities with respect to that of endohedral C₆₀, indicating that the effect of cage size is effective in the second hyperpolarizabilities of endohedral fullerenes. The study will benefit not only the designation and the syntheses of the novel molecular (HF)₂@C₇₀ but also the understanding of the structures and properties of endohedral fullerenes

Self-Assembled Donor–Acceptor Chromophores: Evident Layer Effect on the First Hyperpolarizability and Two-Dimensional Charge Transfer Character

Self-assembled donor–acceptor chromophores have extensive applications in photofunctional devices owing to their unique charge transport properties. To explore the possibility of improving nonlinear optical (NLO) properties by self-assembly to multilayer complexes, we theoretically investigated the geometric and electronic structures, interlayer weak interactions, absorption spectra, charge transfer properties, polarizabilities (α), and first hyperpolarizabilities (β) of naphthalimide, -phenyl, and -naphthyl monomers, dimers, and trimers by increasing the layer number <i>n</i> (<i>n</i> = 1, 2, 3). Different stacking patterns of their dimers were also taken into account. These show that parallel stacking patterns are conducive to maximizing overlap with respect to antiparallel ones due to the concept of optimal π-orbital overlap is more vast than purely maximizing cofacial overlap to improve charge transport. The decreases in band gap for the di/trimeric versus monomeric naphthalimide, -phenyl, and -naphthyl monomers indicate the possibility of more favorable photoinduced electron transition in the aggregate when compared to the monomer. The linear and second-order NLO properties of these complexes are investigated in detail. The α values increase linearly as the increased number <i>n</i> of the layer (<i>n</i> = 1, 2, and 3), providing a new kind of tendency forecast method for the linear optical properties. Along with the increasing electron donating ability of the donor, the β_tot values of monomers increased, revealing the general rule of designing NLO molecular materials. The dependence of β_tot value on the layer number shows that the β_tot value increased with the increased number of layer, which can be rationalized by considering the enhancement of interlayer electronic transition and two-dimensional NLO character with the two charge transfer axes. We hope this work may evoke one’s attention to design new, highly efficient second-order NLO materials with excellent building blocks: multilayer complexes

Nanoscale Polysulfides Reactors Achieved by Chemical Au–S Interaction: Improving the Performance of Li–S Batteries on the Electrode Level

In this work, the chemical interaction of cathode and lithium polysulfides (LiPSs), which is a more targeted approach for completely preventing the shuttle of LiPSs in lithium–sulfur (Li–S) batteries, has been established on the electrode level. Through simply posttreating the ordinary sulfur cathode in atmospheric environment just for several minutes, the Au nanoparticles (Au NPs) were well-decorated on/in the surface and pores of the electrode composed of commercial acetylene black (CB) and sulfur powder. The Au NPs can covalently stabilize the sulfur/LiPSs, which is advantageous for restricting the shuttle effect. Moreover, the LiPSs reservoirs of Au NPs with high conductivity can significantly control the deposition of the trapped LiPSs, contributing to the uniform distribution of sulfur species upon charging/discharging. The slight modification of the cathode with <3 wt % Au NPs has favorably prospered the cycle capacity and stability of Li–S batteries. Moreover, this cathode exhibited an excellent anti-self-discharge ability. The slight decoration for the ordinary electrode, which can be easily accessed in the industrial process, provides a facile strategy for improving the performance of commercial carbon-based Li–S batteries toward practical application

Second-Order Nonlinear Optical Properties of Carboranylated Square-Planar Pt(II) Zwitterionic Complexes: One-/Two-Dimensional Difference and Substituent Effect

Zwitterionic complexes have been the subject of great interest in the past several decades due to their multifunctional application in supramolecular chemistry. Herein, a series of internally stable charge-compensated carboranylated square-planar Pt­(II) zwitterionic complexes have been explored by density functional theory aim to assessing their structures, the first hyperpolarizabilities, first hyperpolarizability densities, and electronic absorption spectra. It is found that the first hyperpolarizabilities of two-dimensional (2D) structure complexes are much larger with respect to the one-dimensional complex. It is ascribed to the lower transition energy and more obvious charge transfer, which can be further illustrated by their large amplitude and separate distribution of first hyperpolarizability density. In addition, the first hyperpolarizabilities of 2D complexes can be further significantly modified by introducing electron-donating/withdrawing groups on the carborane cage. As a consequence, we believe that these 2D zwitterionic complexes can behave as novel second-order nonlinear optical chromophore with a promising future