Molecular interactions in one-dimensional organic nanostructures

Intermolecular interactions involving pi-pi interaction and hydrogen bonding are used to create one-dimensional molecular nanostructures of hexasubstituted aromatics. Site-selective steady state fluorescence, time-resolved fluorescence, scanning electron microscopy, and atomic force microscopy measurements detail the intermolecular interactions that drive the aromatic molecules to self-assemble in solution to form well-ordered columnar stacks. These nanostructures, formed in solution, vary in their number, size, and structure depending on the solvent used. In addition, our results indicate that the substituents/ side groups and the proper choice of the solvent can be used to tune the intermolecular interactions. The 1D stacks and their aggregates can be easily transferred by solution casting, thus allowing a simple preparation of molecular nanostructures on different surfaces.     

Molecular trapping on two-dimensional binary supramolecular networks

Molecular preferential adsorption on molecular patterned surfaces via specific intermolecular interactions provides an efficient route to construct ordered organic nanostructures for future nanodevices. Here, we demonstrate the preferential trapping of second-layer molecules atop two-dimensional binary supramolecular networks, F(16)CuPc on DIP:F(16)CuPc and 6P:F(16)CuPc systems, respectively, through intermolecular π-π interactions. The formation of the second-layer supramolecular nanostructures, individual molecular dots or linear molecular chains, can be controlled by the underlying molecular networks.     

Intermolecular interactions of 1-vinyl-1,2,4-triazole in various solvents

The solvent effect on intermolecular interactions of 1-vinyl-1,2,4-triazole was estimated by ¹H NMR spectroscopy. It was shown that 1-vinyl-1,2,4-triazole molecules form homoassociates (molecular stacks) which are broken on dilution with CCl₄. In polar solvents (dimethylacetamide-d ₆, D₂O), monomer-solvent heteroassociates prevail.     

Supramolecular structure of 6-phenyl-2-chloropyrimidine-4-carboxamide and its complexes with dioxane and ethanol

A stable 2:1 complex of 6-phenyl-2-chloropyrimidine-4-carboxamide with dioxane has been synthesized. The structure of the complex was investigated by molecular spectroscopy (chloroform solution), thermoderivatography, and XRD (crystalline phase). A supramolecular structure is formed in the crystal of the complex, which involves centrosymmetric dimer associates of amide molecules, linked by dioxane molecules and intermolecular hydrogen bonds into infinite stepwise ribbons. These ribbons are stacked via π-stacking pair interactions “amidopyrimidine-amidopyrimidine.” The complex of the same 2:1 carboxamido derivative of pyrimidine with ethanol is unstable and has a different structure. The ethanol molecules lie in the vacant voids of the stacks formed by the “amidopyrimidine-amidopyrimidine” synthon.     

Dynamic cylindrical assembly of triblock copolymers by a hierarchical process of covalent and supramolecular interactions

We have developed a hierarchical process that combines linear triblock copolymers into concentric globular subunits through strong chemical bonds and is followed by their supramolecular assembly via weak noncovalent interactions to afford one-dimensionally assembled, dynamic cylindrical nanostructures. The molecular brush architecture forces triblock copolymers to adopt intramolecular interactions within confined frameworks and then drives their intermolecular interactions in the mixtures of organic solvent and water. In contrast, the triblock copolymers, when not preconnected into the molecular brush architectures, organize only into globular assemblies.     

卟啉类L-B膜分子间相互作用的光谱研究

以无取代的meso-四-(4-N)-吡啶基卟啉及其过渡族金属(主要Cu~(2+)、Zn~(2+))络合物制备L-B膜,以近紫外-可见吸收光谱和荧光光谱为手段,研究叶啉类分子在氯仿溶液中,L-B膜状态下以及固态状态下的相互作用。探讨分子聚集体的存在对光谱性质的影响。 为了研究叶咻类分子间的相互作用及其对光谱性质的影响,我们首先分析了叶啉在CHCl_3溶液中及固态状态下的近紫外-可见吸收光谱和荧光光谱。并将其与叶啉类分子的L-B膜作比较。结果表明,卟啉类的Soret吸收带带宽及峰位置在三种状态下均不相同,L-B膜的情况介于溶液中的和固体下的情况之间,说明了在L-B膜中,卟啉分子存在着某种形式的聚集体,且在这种聚集体中分子间的相互作用程度比固体弱,可以认为L-B膜上的分子呈准晶体状态。     

Rapid self-assembly of oligo(o-phenylenediamine) into one-dimensional structures through a facile reprecipitation route

The self-assembly of oligo(o-phenylenediamine) (OPD) into 1-D nanostructures on a macroscopic length scale was found when they were transferred from N-methyl pyrrolidone to deionized water. Field emission scanning electron microscopy and confocal fluorescence microscopy were used to investigate the morphology of the precipitates. Results showed that large amounts of OPD 1-D supertructures could be obtained through the simple reprecipitation route, and the length of the fibers could be tuned from microscale to macroscale by adjusting the ratio of two solvents. X-ray diffraction patterns and UV-vis spectra revealed that pi-pi interactions between OPD molecules that facilitated the formation of 1-D structures became predominant when they were transferred from a good solvent to a bad one. Accordingly, a possible formation mechanism was proposed.     

Characterization, supramolecular assembly, and nanostructures of thiophene dendrimers

We report the synthesis and characterization of dendritic thiophene derivatives with their unique supramolecular assembly into 2-D crystals, nanowires, and nanoparticle aggregates. The structure and size of the dendrons and dendrimers have been confirmed with various techniques, such as NMR, SEC, and MALDI-TOF-MS. The mass values were consistent with the mass observed by MALDI-TOF-MS, whereas SEC measurements also gave useful information on the hydrodynamic volume of the individual dendrimers. The interesting electrooptical properties were highlighted by very broad absorption spectra and narrower fluorescence consistent with their electrochemical behavior. The self-organization of the dendrimers on the solid substrate is dependent on the nature of the substrate, preparation methods, and the molecule-molecule and molecule-substrate interactions. Thus, 14T-1 and 30T both formed globular aggregates on mica surface, while 14T-1 also formed nanowires on graphite surface. On the other hand, the larger 30T was observed to form 2-D crystalline structures. By varying the alkyl chain length attached to 14T-1, we were also able to obtain 2-D crystals on graphite. This showed that the different symmetry of packing for 30T and 14T-1 is also dependent on several factors, such as the molecular shape, size, and the presence of noncovalent intermolecular interactions. The results demonstrated the unique ability of thiophene dendrimers to form nanostructures on surfaces.     

A discrete metallocyclic complex that retains its solvent-templated channel structure on guest removal to yield a porous, gas sorbing material

A discrete rectangular metal-organic complex that stacks to form one-dimensional channels filled with acetonitrile solvent molecules is described. Removal of the solvent under relatively mild conditions proceeds via a single-crystal to single-crystal transformation that leaves the host lattice unaltered. These findings proffer a design strategy for porous materials based on the simple principle that rigid molecular rings cannot pack efficiently and would thus favor the inclusion of guest species whenever possible. Upon guest removal, an efficiently packed new phase can then only be achieved by means of bond cleavage. Thus, achieving crystal porosity by maintaining robust metal-ligand coordination bonds in such discrete cyclic systems directly parallels the strategy employed for MOFs.     

溶剂交换法制备一维有机纳米材料

利用溶剂交换法制备了几种有机小分子化合物的一维纳米材料,并分别用SEM、TEM、XRD等对其结构进行了表征.分析了纳米材料的生长过程,讨论了有关的机理,并研究了其吸收光谱和荧光光谱等光物理行为.结果显示,有机纳米结构的形貌和尺寸对分子聚集体的光谱性质具有调制作用,使得它们展示出不同于溶液和体材料的优良纳米特性.     

4‐Iodoquinoline

Nearly planar molecules of the title compound, C₉H₆IN, are packed in inclined stacks along the short crystallographic b axis and molecules in adjacent stacks are packed to form antiparallel zigzag chains. Short intermolecular N...I contacts [3.131 (3) Å] are observed between molecules in adjacent stacks. A network of C—H...π hydrogen bonds [2.821 (5) and 3.083 (3) Å] between molecules in adjacent stacks is also present. These motif‐generating interactions, including the weak C—H...π interactions, are of relevance in crystal engineering and design.     

Controllable Self‐Assembly of Amphiphilic Zwitterionic PBI Towards Tunable Surface Wettability of the Nanostructures

Amphiphilic molecules have received wide attention as they possess both hydrophobic and hydrophilic properties, and can form diverse nanostructures in selective solvents. Herein, we report an asymmetric amphiphilic zwitterionic perylene bisimide ( AZP ) with an octyl chain and a zwitterionic group on the opposite imide positions of perylene tetracarboxylic dianhydride. The controllable nanostructures of AZP with tunable hydrophilic/hydrophobic surface have been investigated through solvent‐dependent amphiphilic self‐assembly as confirmed by SEM, TEM, and contact angle measurements. The planar perylene core of AZP contributes to strong π–π stacking, while the amphiphilic balance of asymmetric AZP adjusts the self‐assembly property. Additionally, due to intermolecular π–π stacking and solvent–solute interactions, AZP could self‐assemble into hydrophilic microtubes in a polar solvent (acetone) and hydrophobic nanofibers in an apolar solvent (hexane). This facile method provides a new pathway for controlling the surface properties based on an asymmetric amphiphilic zwitterionic perylene bisimide.     

Aggregates of poly-functional amphiphilic molecules in water and oil phases

The solvation and aggregate formation of complex amphiphilic molecules such as tetra-acids in polar and nonpolar phases are studied via Molecular Dynamics simulations. The nonpolar core of tetra-acid molecules is found to be effectively impermeable for water molecules resulting in a low solubility in the polar solvent, while nonpolar solvent molecules sufficiently solvate the amphiphilic molecules considered, enabling an open conformation of their molecular structure. The rigidity of the core region of the tetra-acid molecules has been found to play a crucial role in their behavior in both polar and nonpolar phases. In the polar phase, simulations have shown that tetra-acids form micelle-like structures with a small aggregation number, confirming previous experimental work. The identification of a case of study in which micelle-like structures can form only with a small aggregation number enables the study via Molecular Dynamics of micelle-micelle interactions. Micelle stability and dispersion in the polar phase under different conditions can be therefore investigated. In the nonpolar phase, the preferential interactions between carboxyl groups, the affinity of the tetra-acids with the solvent molecules, and the structural characteristics of the central core moiety of the tetra-acids have been found to possibly induce a web like array, or network.     

Computational study of solvent effects on the molecular self-assembly of tetrolic acid in solution and implications for the polymorph formed from crystallization

The solution behavior of a model compound, tetrolic acid (TTA), is studied via molecular dynamics simulations in four organic solvents. The results suggest that strong interactions between TTA and solvent molecules (ethanol or dioxane) prevent the formation of carboxylic acid dimers in solution and thus promote the crystallization of TTA in a catemer-based form or a solvate form. Weak interactions, however, between TTA and solvent molecules (carbon tetrachloride or chloroform) facilitate the formation of carboxylic acid dimers in solution and thus promote the crystallization of a dimer-based crystal. Detailed solvent structure plays an important role in determining the relative stability of various growth synthons in solution and also the barriers along the pathway connecting them. This work illustrates the potential of molecular simulations to aid in the rational selection of solvents to obtain desired polymorphs during crystallization.     

Effect of weak interactions on the H...H distance in stretched dihydrogen complexes

Computational and experimental results presented in this paper demonstrate that the H-H distance in stretched dihydrogen complexes can be hypersensitive to a variety of weak intra- and intermolecular interactions, including those with bulky ligands and solvent molecules, hydrogen-bonding interactions, or ion-pairing. Particularly, the complex IrH(H...H)Cl(2)(P(i)Pr(3))(2) which contains a stretched dihydrogen ligand in the crystalline form, as shown by neutron diffraction, is a trihydride in solution. The difference is due to the intermolecular Ir-Cl...H-Ir hydrogen bonding in the solid.     

Monomer and Excimer Emission in a Conformational and Stacking-Adaptable Molecular System

A design strategy that combines molecular conformation, alkyl chain length, and charge-transfer effects has been developed to obtain conformational and stacking-adaptable donor-acceptor-π type molecules for precisely regulating the monomer and excimer emission in a single luminous platform under different environments. These fluorophores can exhibit bright monomer emissions when they are in the dispersed state based on their planar conformation. However, when the luminous molecules with short alkyl side chains are in the crystalline state, their molecular conformation can become distorted, further inducing strong intermolecular interactions and staggered π-π stacking for bright excimer emission. More importantly, their dispersed and aggregated states can be reversibly regulated in a phase-change fatty acid matrix, to achieve temperature-responsive fluorescence for temperature monitoring and advanced information encryption.     

Electron transfer in a radical ion pair: quantum calculations of the solvent reorganization energy

Results are presented for an investigation of intermolecular electron transfer (ET) in solution by means of quantum calculations. The two molecules that are involved in the ET reaction form a solvent-separated radical ion pair. The solvent plays an important role in the ET between the two molecules. In particular, it can give rise to specific solute-solvent interactions with the solutes. An example of specific interactions is the formation of a hydrogen bond between a protic solvent and one of the molecules involved in the ET. We address the study of this system by means of quantum calculations on the solutes immersed in a continuum solvent. However, when the solvent can give rise to hydrogen bond formation with the negatively charged ion after ET, we explicitly consider solvent molecules in the solute cavity, determining the hydrogen bond energetic contribution to the overall interaction energy. Solute-solvent pair distribution functions, showing the different arrangement of solvent molecules before and after ET in the first solvation shell, are reported. We provide results of the solvent reorganization energy from quantum calculations for both the two isolated fragments and the ion pair in solution. Results are in agreement with available experimental data.     

基于四联苯臂星型小分子凝胶剂的TNT薄膜荧光传感器

基于具有三苯胺中心核、咔唑外围和四联苯连接臂的星型荧光小分子三(4″″-(3, 6-二叔丁基-咔唑-9氢-9-基)-(1, 1': 4', 1″':4″', 1?:4?, 1″″-四苯基)-4-基)胺(N5), 采用溶液旋涂的方法制备了用于检测三硝基甲苯(TNT)饱和蒸汽的高效荧光传感薄膜。 不同于具有单苯连接臂的模型化合物三(4'-(3, 6-二叔丁基-咔唑-9氢-9-基)-(1, 1'-二苯基)-4-基)胺(N2), N5由于长共轭臂的存在, 容易在苯类溶剂中通过π-π相互作用组装形成凝胶。 同时, 其旋涂薄膜具有细小纳米级纤维状的组装形貌, 表面出现一定的多孔结构, 有利于气体分子的渗透。 因此, 应用于TNT蒸汽的检测, 化合物N5薄膜表现出比N2薄膜更快的荧光淬灭响应速度和更高的淬灭效率。 特别是TNT传感特性几乎不受化合物N5膜厚的影响, 当膜厚为94 nm时, 在1和30 min的淬灭程度仍然可以达到44%和90%。     

Exciplex fluorescence as a diagnostic probe of structure in coordination polymers of Zn2+ and 4,4'-bipyridine containing intercalated pyrene and enclathrated aromatic solvent guests

Coordination polymers based on Zn(II)-4,4'-bipyridine (Zn-bipy) frameworks containing pyrene intercalated between adjacent layers and aromatic solvent molecules enclathrated within the framework cavities have been prepared and characterized for the first time. These compounds are highly fluorescent, and show broad, featureless emission spectra significantly red-shifted relative to pyrene monomer fluorescence; this has been assigned to pyrene-bipy exciplex emission. Single-crystal X-ray structural analysis shows that the presence of the aromatic solvent molecule within the cavities has a profound effect on the architecture of these frameworks: in the case of benzene, toluene, p-xylene, and chlorobenzene, the Zn-bipy framework consists of 1-D ladders, whereas in the case of o-dichlorobenzene (the largest solvent guest), the framework was based on a 2-D square grid. This difference in stoichiometry and architecture was also reflected in significant differences in the fluorescence of these coordination polymers, with three of the four compounds with 1-D ladder geometries having similar fluorescence maxima (ca. 520 nm) and lifetimes (ca. 70 ns), whereas the compound with square grid topology had a significantly blue-shifted maximum (ca. 460 nm) and shorter lifetime (ca. 42 ns). It is proposed that exciplexes form upon excitation of ground-state complexes, involving face-to-face bipy/pyrene complexes (pi-pi stacking interactions) in the case of the 1-D ladder structures, but edge-to-face bipy/pyrene and pyrene/o-dichlorobenzene complexes (C-H...pi interactions) in the case of the 2-D square grid structure.     

Ordered arrays of semi-crown ligands on an Au(111) electrode surface: in situ STM study

Self-organized systems have attracted much at-tention due to their potential applications in nano- technology as a bottom-up?approach for the con-struction of molecule-scale devices and nanostruc-tures[1—4]. Beyond the self-assembly of small molecu-lar building blocks, Schnherr et al. recently suc-ceeded in arranging the rosette supramolecular nanos-tructures in two dimensions on HOPG[5,6]. Moreover, interest has tremendously increased in the su-pramolecular structures via coordination-dr…