Vibrational Normal Modes of an Equilateral Triangular Mechanical Molecule

Three point-like massive particles/atoms are connected with three springs forming an equilateral triangle replicating a prototype triatomic molecule. The triangle is inscribed within a stationary frame via three additional springs confining the vibrations of the molecule to a 2D space. It is the objective of this research flavored investigation to seek the normal vibrational modes for this three-body six-spring structure. The entire analysis including symbolic, numeric, and graphics is carried out by adapting a suitable Computer Algebra System (CAS), Mathematica. For a comprehensive understanding, the frequency of the normal mode is used for a visual animation;an actual mechanical replica of the “molecule” for the scenario on hand is fabricated.

Predicting Rate Constants for Nucleophilic Reactions of Amines with Diarylcarbenium Ions Using an ONIOM Method

The rate constants of the nucleophilic reactions between amines and benzhydrylium ions were calculated using first-principles theoretical methods. Solvation models including PCM, CPCM, and COSMORS, as well as different types of atomic radii including UA0, UAKS, UAHF, Bondi, and UFF, and several single-point energy calculation methods （B3LYP, B3P86, B3PW91, BHANDH, PBEPBE, BMK, M06, MP2, and ONIOM method） were examined. By comparing the correlation between experimental rate constants and the calculated values, the ONIOM（CCSD（T）/6-311＋＋G（2df,2p）：B3LYP/6-311＋＋G（2df,2p））//B3LYP/6- 31G（d）/PCM/UFF） method was found to perform the best. This method was then employed to calculate the rate constants of the reactions between diverse amines and diarylcarbenium ions. The calculated rate constants for 65 reactions of amines with diarylcarbenium ions are in agreement with the experimental values, indicating that it is feasible to predict the rate constant of a reaction between an amine and a diarylcarbenium ion through ab initio calculation.

A Possible Pumping Mechanism for Interstellar Class Ⅱ107 GHz Methanol Masers

It is recognized that the interstellar methanol-107GHz masers and OH-4.765 GHz masers towards Class II sources are associated with each other and coexist towards ultracompact HII regions. Therefore we suggest a new pumping mechanism - methanol masers without population inversion. It can explain the formation of 107GHz methanol masers, with the 4.765 GHz OH masers acting as a driving coherent microwave field. It is argued that this mechanism is compatible with the astronomical conditions.

Strengthening and toughening styrene-butadiene rubber by mechanically interlocked cross-links

Styrene-butadiene rubber(SBR)is an indispensable material in modern society,and the necessity for enhanced mechanical properties in SBR persists,particularly to withstand the rigors of challenging environmental conditions.To surmount the limitations of conventional cross-linking modes,mechanical bonds stabilized by host-guest recognition are incorporated as the cross-linking points of SBR to form mechanically interlocked networks(MINs).Compared with covalently cross-linked network,the representative MIN exhibits superior mechanical performance in terms of elongation(1392%)and breaking strength(4.6 MPa),whose toughness has surged by 17 times.Dissociation of host-guest recognition and subsequent sliding motion provide an effective energy dissipation mechanism,and the release of hidden length is also beneficial to enhance toughness.Furthermore,the introduction of the rotaxane cross-links made the network more pliable and possess damping and elastic properties,which can return to initial state with one minute rest interval.We aspire that this direct introduction method can serve as a blueprint,offering valuable insights for the enhancement of mechanical properties in conventional commercial polymer materials.

Stretchable poly[2]rotaxane elastomers

Mechanically interlocked polymers(MIPs)are promising candidates for the construction of elastomeric materials with desirable mechanical performance on account of their abilities to undergo inherent rotational and translational mechanical movements at the molecular level.However,the investigations on their mechanical properties are lagging far behind their structural fabrication,especially for linear polyrotaxanes in bulk.Herein,we report stretchable poly[2]rotaxane elastomers(PREs)which integrate numerous mechanical bonds in the polymeric backbone to boost macroscopic mechanical properties.Specifically,we have synthesized a hydroxyfunctionalized[2]rotaxane that subsequently participates in the condensation polymerization with diisocyanate to form PREs.Benefitting from the peculiar structural and dynamic characteristics of the poly[2]rotaxane,the representative PRE exhibits favorable mechanical performance in terms of stretchability(∼1200%),Young’s modulus(24.6 MPa),and toughness(49.5 MJ/m^(3)).Moreover,we present our poly[2]rotaxanes as model systems to understand the relationship between mechanical bonds and macroscopic mechanical properties.It is concluded that the mechanical properties of our PREs are mainly determined by the unique topological architectures which possess a consecutive energy dissipation pathway including the dissociation of host−guest interaction and consequential sliding motion of the wheel along the axle in the[2]rotaxane motif.

A supramolecular oligo[2]rotaxane constructed by orthogonal platinum(Ⅱ) metallacycle and pillar[5]arene-based host–guest interactions

Oligo[n]rotaxanes are one of the most extensively studied categories of mechanically bonded macromolecules.In this study,a supramolecular oligo[2]rotaxane is successfully constructed driven by platinum(Ⅱ)metallacycle and pillar[5]arene-based host–guest interactions in an orthogonal way.The supramolecular oligo[2]rotaxane is further applied in fabricating a light harvesting system.

Sequence Engineering in Tuning the Circularly Polarized Luminescence of Aggregation-Induced Emission-Active Hetero[3]rotaxanes

Based on a[2]rotaxane precursor with exchangeable pentafluorophenyl ester stoppers,a new wheelassembling approach has been successfully developed for the precise sequence control of hetero[3]rotaxanes,leading to the facile and efficient synthesis of both sequence isomers of hetero[3]rotaxanes.More importantly,taking advantage of the chirality retention along with the wheel-assembling process,corresponding sequence isomers of chiral AIEgenfunctionalized hetero[3]rotaxanes were further precisely synthesized.Impressively,the resultant hetero[3]rotaxanes revealed remarkable sequencedependent aggregation-induced emission(AIE)behavior and circularly polarized luminescence performance with large dissymmetry factors up to 0.012,highlighting the great power of the newly coined sequence engineering concept in developing novel AIE-active chiroptical materials.This proof-ofconcept study lays the foundation for investigation of the structure-property relationships of heterorotaxanes that can further direct the rational design and precise synthesis of sequence-defined heterorotaxanes with desirable properties for practical applications.

Seeing Is Believing:Directly Imaging Contractions of Artificial Molecular Muscles with Platinum Atom Markers

Artificial molecular muscles undergo well-controlled contractile and extensile motions upon external stimulation,leading to remarkable length changes.Evaluating such length changes at the molecular level is essential to the design of integrated artificial molecular muscles that mimic biological muscles.Taking advantage of the strong contrast of platinum(Pt)atoms in high-angle annular dark-field scanning transmission electron microscopy images,we imaged Pt-containing molecular[c2]daisy chains directly by employing metal atom markers.The length changes and associated conformational transformations of these newly developed artificial molecular muscles have been measured experimentally in combination with theoretical calculations.The contraction ratios of these two molecular muscles with the TEMPO or pyrene anchoring group were calculated to be 21.0%or 15.7%respectively,suggesting a substantial anchoring effect.This study demonstrates the experimental measurement of the length changes of artificial molecular muscles and provides a new avenue for investigating the motion of artificial molecular machines.

Lighting up rotaxanes with AIEgens

Aiming at the construction of novel rotaxanes with desired luminescent properties for practical applications, recently the rapid development of rotaxanes decorated with aggregation-induced emission(AIE) luminogens(i.e., AIEgens) has been witnessed. The combination of AIEgens and rotaxanes leads to the successful construction of a novel type of luminescent rotaxanes with many attractive features. In particular, the unique controllable dynamic feature of rotaxanes endows the resultant AIEgen-based rotaxanes precisely tunable emissions under external stimuli, leading to the construction of a novel type of smart luminescent materials. In this minireview, the recent progress of AIEgen-based rotaxanes has been summarized, with an emphasis on the design strategy and potential applications.

Applying reticular synthesis to the design of Cu-based MOFs with mechanically interlocked linkers

The concept of“robust dynamics”describes the incorporation of mechanically interlocked molecules(MIMs)into metal-organic framework(MOF)materials such that large amplitude motions(e.g.,rotation or translation of a macrocycle)can occur inside the free volume pore of the MOF.To aid in the preparation of such materials,reticular synthesis was used herein to design rigid molecular building blocks with predetermined ordered structures starting from the well-known MOF NOTT-101.New linkers were synthesized that have a T-shape,based on a triphenylene tetra-carboxylate strut,and their incorporation into Cu(II)-based MOFs was investigated.The single-crystal structures of three new MOFs,UWCM-12(fof),β-UWCM-13(loz),UWCM-14(lil),with naked T-shaped linkers were determined;β-UWCM-13 is the first reported example of the loz topology.A fourth MOF,UWDM-14(lil)is analogous to UWCM-14(lil)but contains a[2]rotaxane linker.Variable-temperature,^(2)H solid-state NMR was used to probe the dynamics of a 24-membered macrocycle threaded onto the MOF skeleton.

Whither Second-Sphere Coordination?

The properties of coordination complexes are dictated by both the metals and the ligands.The use of molecular receptors as second-sphere ligands enables significant modulation of the chemical and physical properties of coordination complexes.In this minireview,we highlight recent advances in functional systems based on molecular receptors as second-sphere coordination ligands,as applied in molecular recognition,synthesis of mechanically interlocked molecules,separation of metals,catalysis,and biomolecular chemistry.These functional systems demonstrate that second-sphere coordination is an emerging and very promising strategy for addressing societal challenges in health,energy,and the environment.