Atomistic Insight Into the Host–Guest Interaction of a Photoresponsive Metal–Organic Framework

Photoresponsive functional materials have gained increasing attention due to their externally tunable properties. Molecular switches embedded in these materials enable the control of phenomena at the atomic level by light. Metal–organic frameworks (MOFs) provide a versatile platform to immobilize these photoresponsive units within defined molecular environments to optimize the intended functionality. For the application of these photoresponsive MOFs (pho-MOFs), it is crucial to understand the influence of the switching state on the host–guest interaction. Therefore, we present a detailed insight into the impact of molecular switching on the intermolecular interactions. By performing atomistic simulations, we revealed that due to different interactions of the guest molecules with the two isomeric states of an azobenzene-functionalized MOF, both the adsorption sites and the orientation of the molecules within the pores are modulated. By shedding light on the host–guest interaction, our study highlights the unique potential of pho-MOFs to tailor molecular interaction by light.     

Stability and bifurcation analysis in the delay-coupled van der Pol oscillators

In this paper, the dynamics of a system of two van der Pol equations with a finite delay are investigated. We show that there exist the stability switches and a sequence of Hopf bifurcations occur at the zero equilibrium when the delay varies. Using the theory of normal form and the center manifold theorem, the explicit expression for determining the direction of the Hopf bifurcations and the stability of the bifurcating periodic solutions are derived.     

Adsorption of a single polymer chain on a surface: A molecular dynamics simulation study

We performed simulations of the physical adsorption of a single globular chain on a surface of hemispherical shape by means of molecular dynamics simulations. For the chain, we took advantage of a united atom model. Interactions within the chain were limited to stretching, bending, and torsional as well as nonbonded interactions between the nonadjacent atoms. The interaction between each chain element and the surface formation are reigned by a Lennard–Jones potential. In this article, we focused on differences in the behavior of the adsorbed globule to the free unadsorbed one particularly in two different zones of the immediate vicinity of the surface. There were strong indications for a localized acceleration of the dynamics as compared with the bulk that appears in an increase of trans–gauche switches. For explanation we came up with an adsorption scenario. Special attention was given to the shift of the percentage of trans and gauche conformations within the globule in dependence on the strength of the adsorption potential that might be related to crystallization or glass transition. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2333–2339, 2001     

两端对称负折射率缺陷复合光子晶体:多通道滤波和光开关

采用传输矩阵法对两端对称负折射率缺陷复合光子晶体结构[D(AB)mD]N的透射特性进行了研究.结果表明:当N=2时,该结构透射谱的禁带出现两个完全共振透射峰,当N增加时,每个共振透射峰又分裂为N-1条；当复合光子晶体的层数m逐渐增加时,透射峰的品质因子逐渐提高,且分裂的共振透射峰距离逐渐减少；既为该结构实现高品质的多通...     

Supramolecular Metal Ion Sensing using Luminophoric Labels based on Ruthenium(II) Bis-terpyridine and Tris-bipyridine Scaffoldings

Two unique systems are described where modification of the photophysical properties is observed in the presence of an adventitious cation. In the first system an enhancement of the emission properties of linear ruthenium(II) bis-terpyridine bearing a central chelating centre is found. In the second system restoration of the emissive properties of the chromophore is observed due to a conformation control of intramolecular electron transfer in a calix[4]quinone bearing an appended ruthenium(II) tris-bipyridine chromophore.     

All optical switching in semiconductor microresonators based on pattern selection

We present here a method for selecting optical patterns in a passive semiconductor microresonator, by using a spatial perturbation. A pattern is spontaneously generated in the system, and a switching beam causes this pattern to rotate even if the power in the switching beam is much lower than the power in the pattern. Thus, an all optical switch is realized, that operates at low light levels.     

Modulation of photoswitching profiles by 10,11-dialkoxymethyl substituents in c(2)-symmetric dibenzosuberane-based helicenes

A series of C₂‐symmetric, 10,11‐disubstituted dibenzosuberane (DBS)‐based helicenes 6 a – c with a common 7‐bromo‐α‐tetralin‐based bottom fragment were synthesized. Their absolute stereochemistry was determined to be 10R,11R,P after reductive desulfurization of the corresponding (10R,11R,1′S)‐episulfides with complete stereospecificity. Photoisomerization of the diastereomerically pure (P)‐ 6 c in hexane led to virtually exclusive formation of the opposite M‐form diastereomer (P/M′, <1:>99) at 290 nm. The preferential return of (M′)‐ 6 c to (P)‐ 6 c was also achieved with high selectivity (P/M′, 90:10) at 330 nm. Molecular simulations of (P)‐ 6 c and (M′)‐ 6 c with both DBS conformations suggest that the selectivities of photoswitching are controlled by the conformation of the top DBS template as evidenced by their ¹H NMR spectra. Doping 6 c into a nematic liquid crystal (E7) led to a cholesteric mesophase with modulated pitches, reversible helical senses, and with a switch memory of ternary logic.