Yizhong Yuan

Micellization coupled with facilitation of J-aggregation for poly(1,3-cyclohexadiene)-based amphiphilic block copolymers

Amphiphilic PS-b-sPCHD copolymers can associate to form micelles with PS blocks as the core surrounded by sPHCD blocks in aqueous media. J-Aggregation of the chromophores in sPCHD blocks is significantly facilitated by the micellization, resulting in a remarkable change in the photophysical properties of PS-b-sPCHD.

Spirooxazine-based multifunctional molecular switches with tunable photochromism and nonlinear optical response

A new type of organic photochromic spirooxazine has been synthesized, incorporating increasing numbers of thiophene units by vinyl bridges. These compounds exhibit tunable photochromic properties that are sensitive to low-energy visible light compared with traditional UV. Furthermore, the ring-opening mechanism is put in relation to the interaction of fragment molecular orbitals. The result shows that the effective excitation with significant intensity is centred mainly on the naphthoxazine part and vinyl thiophene plays a crucial role in the photochemical and photophysical process. Density functional calculations are performed to rationalize the “on and off” switching nonlinear optical behaviors of compounds, showing the potential for applying the materials in nonlinear optical switches.

Theoretical studies on molecular and structures of mono- and binuclear chromium carbazole derivatives for optoelectronics.

Studies on the molecular geometries, electronic properties and second-order nonlinearities of a series of mono- and binuclear chromium carbazole complexes: (N-vinylcarbazole)Cr(CO)(3) (M1), (N-vinylcarbazole)Cr(CO)(2)PPh(3) (M2), (CO)(3)Cr(N-vinylcarbazole)Cr(CO)(3) (B1), and (CO)(3)Cr(N-vinylcarbazole)Cr(CO)(2)PPh(3) (B2) were carried out, using the density functional theory (DFT) at the B3LYP//LanL2DZ/6-31G(d) level. The experimental singlet metal-to-ligand charge transfer ((1)MLCT) spectra of these complexes can also be well simulated and discussed by the time-dependent DFT (TDDFT) at the B3LYP//LanL2DZ/6-311+G(d) level associated with the polarizable continuum model (PCM). The computational results show that an unusual characteristic of chromium carbazole structures is explained in terms of interaction between frontier molecular orbitals of the metal and its ligands. The highest occupied molecular orbitals (HOMOs) of these complexes are composed of a set of distorted degenerated Cr 3d orbitals, whereas the lowest unoccupied molecular orbitals (LUMOs) are predominantly the N-vinylcarbazole ligand π* orbitals. The HOMO-LUMO energy gaps decrease in the order NVC > M1 > B1 > M2 > B2. The considerable coupling between the carbazole and (CO)(3) in M1 creates an asymmetric environment about the chromium atom, leading to modest second-order responses. The PPh(3) ligand is acting as a donor which increases the donating strength of the d(π) orbitals in chromium carbazole species, resulting in the large electronic asymmetry in M2. As for the binuclear chromium carbazole chromophores, a wide-range (1)MLCT band and large oscillator strength are found, allowing for the electronic interactions between two metal centers which can be modified by altering the ligand bound to the metals to induce peculiar asymmetry. Essentially, Cr(CO)(3) acceptor and Cr(CO)(2)PPh(3) donor units in B2 make significant contribution to the charge-transfer process or NLO responses via conventional push-pull chromophoric architecture.

Preparation of starch-g-PMMA, starch-g-P(MMA/BMA) and starch-g-P(MMA/MA) nanoparticles and their reinforcing effect on natural rubber by latex blending: a comparative study

Nanoparticles including starch-graft-methylmethacrylate, starch-graft-(methylmethacrylate/methyl acrylate), starch-graft-(methyl methacrylate/butyl methacrylate) were synthesized via emulsifier-free emulsion polymerization and were blended with natural rubber latex at various mass ratios. Chemical structure of graft copolymers was confirmed by Fourier transform infrared. Transmission electron microscopy demonstrated the core-shell structures of the nanoparticles distributed uniformly around the natural rubble particles. The tensile strength of blend films was significantly enhanced by addition of graft copolymers. Besides, scanning electron microscopy and atomic force microscopy showed the blend film had smooth surface.

Assessment of range‐separated exchange functionals and nonempirical functional tuning for calculating the static second hyperpolarizabilities of streptocyanines

DFT method can severely overestimate the response properties for π‐conjugation systems. The range‐separated exchange and recently developed optimal IP‐tuning process are evaluated on the prediction of static second hyperpolarizabilities of streptocyanines of increasing molecular length. The finite field results have shown that the exact exchange at midium and long distance can relieve only a part of the overshooting but still beyond satisfaction. The exact exchange at short distance has the oppsite effects showing the failure of converntional hGGA. The optimal tuned range‐separated exchange functionals show little improvements performing worse than the default ones. Importantly, the electronic structure–property relationship, bond order alternation‐γ, is not well established with DFT method.

Recognition of halides and Y-shaped oxoanions by carbonylchromium-based urea-like molecules: A theoretical analysis of hydrogen bonding modes

One of the major challenges in anion recognition is to design hosts that can be used to distinguish between anions of different shapes. Urea-based molecules are widely used in anion recognition because the pair of -NH groups acts as an electron acceptor. Although these hosts can bind to both spherical anions (halides) and Y-shaped anions (oxoanions), experimental evidence to date does not provide a clear picture of what differences in the nature of the hydrogen bonding interactions could be used to distinguish between anions of different shapes. Here, we use several computational topology analyses to study the non-covalent interactions between Cr(CO)3-based organometallic urea-like hosts and halides and Y-shaped oxoanions. Our results suggest that the F(-) and AcO(-) anions are recognized experimentally due to a combination of strong interaction and large infrared (IR) shifts upon complexation, verifying the remarkable IR-reporting ability of the Cr(CO)3 moiety and its potential applications in anion recognition. The lone pairs of the oxygen atom in Y-shaped oxoanions directly interact with the -NH groups of the hosts, while all the shell electrons of the halides participate as a group in the interaction; however, the relative contributions of electrostatic and charge-transfer interactions are quite similar for the two types of anions. This insight into the nature of the anion-host interactions can be used to provide guidance for the design of hosts that differentiate between anions.

Studies of latex blends of natural rubber/poly(methyl methacrylate-co-2-ethylhexyl methacrylate) and their comparison with incompatible natural rubber/poly(methyl methacrylate)

Poly(methyl methacrylate-co-2-ethylhexyl methacrylate) copolymers with 0.6–49.2 mol% of 2-ethylhexyl methacrylate were synthesized and blended with natural rubber at three different blend ratios (i.e. 5/95, 10/90, 15/85) on the latex stage. Chemical structure of the copolymer was confirmed by FTIR and 1H NMR spectroscopy. Mechanical strength of the blend (rubber/copolymer) containing 7.76 mol% of 2-ethylhexyl methacrylate showed the higher values than the incompatible blend natural rubber/PMMA. According to water absorption and ATR-FTIR measurements, the amount of dispersed particles of obtained blends on the surface decreases sharply compared to rubber/PMMA blend. Scanning electron microscopy and atomic force microscopy also showed that surface and cross-section morphologies of the studied were more homogeneous than those of incompatible blend. The miscibility of studied blend was further reflected by DSC analysis.

Design of single-molecular logical devices based on multistable photochromatic spirooxazine

The transition condition and performance of tristate photochromatic spirooxazine have been studied. The characteristics of different photochromatic spirooxazine absorption spectra have been used to construct three kinds of logic devices. These molecular logic devices not only can be controlled by photochemical bistable states but also exhibit excellent photon resistance.