Kang Yeol Lee

Anisotropic Assembly of Ag Nanoprisms

The Ag nanoprisms with controlled arrangements show distinct optical, crystallographic, and surface-enhanced Raman scattering properties depending on their orientation in the assemblies, demonstrating that the controlled assembly of anisotropic nanostructures can be utilized as a powerful tool for studying their physicochemical properties and for the creation of new classes of functional materials.

Fabrication of nanoporous superstructures through hierarchical self-assembly of nanoparticles†

Highly-extended self-supporting nanoporous Au and Au–Ag alloy thin films can be successfully prepared by a self-assembly method with metal nanoparticles as starting building blocks. The size, structure, and composition distribution of the synthesized nanoporous films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction. The experimental results revealed that thermal activation and photoinduced attractive force of nanoparticles cause the particles to be assembled at the air–water interface. The pore size of this new nanoporous material can be controlled by varying the nanoparticle size.

γ-CuI Nanocrystals from Self-Assembled Coordination Polymers

The architectural control of nanocrystals has attracted remarkable attention because of intriguing size-, shape-, and special orientation-dependent properties. Understanding of the properties of individual nanocrystals will enable us to exploit them, making it possible to design and build novel electronic, magnetic, and photonic devices and other functional materials based on these nanostructures. The utilization of coordination compounds as both precursor and template is one of the versatile ways for the preparation of nanomaterials. There are few reports which utilize coordination polymers to synthesize metal oxides, sulfides, and nanowires. Despite these advances, it is still a challenge to develop a synthetic approach which can predict the size and shape of the nanomaterials with respect to the reactants. The preparation of CuI has been carried out by several different methods, such as liquid-phase reaction, laser deposition, vacuum evaporation, and solvothermal techniques. Herein we report the syntheses of two self-assembled Cu coordination polymers 1 and 2, crystal transformation from 1 and 2 into an intermediate Cu coordination polymer 3 with g-CuI nanocrystals and 1,4-bis(2-methylthioethoxy)benzene L by heating the polymers. We also describe that thermal decomposition of the Cu polymer 3 results in g-CuI nanocrystals and L. Scheme 1 shows the syntheses of microcrystals of the two copper(I) coordination polymers [Cu4I4L ACHTUNGTRENNUNG(MeCN)2]n (1) and [Cu8I8L3ACHTUNGTRENNUNG(MeCN)2]n (2) by the self-assembly of CuI and L. Heating both 1 and 2 near 105 8C resulted in [Cu4I4L2]n (3) and g-CuI nanocrystals known as a p-type semiconductor with a band gap of about 3.1 eV. The polymer 3 decom-

Non-Phase-Transition Luminescence Mechanochromism of a Copper(I) Coordination Polymer

A copper(I) coordination polymer, [Cu2I2L2]n (CP 1), shows luminescence mechanochromism with a color change from greenish-blue to yellow upon the application of pressure. Powder X-ray diffraction and Raman studies reveal that the changes in the bond lengths in crystalline CP 1 are the main cause of luminescence mechanochromism. The luminescence mechanochromic process of CP 1 preserves its crystallinity with a small lattice distortion, despite very high pressure, and it is a non-phase-transition process. After the addition of several drops of acetonitrile to the ground and compressed samples, the original greenish-blue emissive and crystalline states are restored. Therefore, the luminescence color conversion processes are fully reversible.

Novel surfactant-free multi-branched gold stars characterized by inverse photocurrent

Multi-branched gold stars were spontaneously formed on a semiconductor (Ge) substrate in high yield via a surfactant-free galvanic displacement method at room temperature using a DMF–water (9/1) mixed solvent. The average length of the branches was estimated to be 561 nm, and the size and shape of the multi-branched gold stars can be controlled by varying the reaction time of the Ge wafer and gold precursor. A high volume ratio of DMF was found to be crucial for the formation of these multi-branched gold stars. Interestingly, the photocurrent of the prepared gold stars decreased by 10% upon irradiation with a 532 nm visible laser. The photocurrent was switched on and off >10 times without significant degradation, indicating high reproducibility and reliability of the inverse photoresponse of the gold stars under visible light.

Reversible Crystal Transformations and Luminescence Vapochromism by Fast Guest Exchange in Cu(I) Coordination Polymers

Six Cu(I) coordination polymers (CPs)-[Cu2I2L2]n (1), {[Cu2I2L2]·2MeCN}n (2), [Cu4I4L2]n (3), {[Cu4I4L2]·CH2Cl2}n (4), {[Cu4I4L2]·CHCl3}n (5), and {[Cu4I4L2]·C6H6}n (6)-were synthesized by self-assembly reactions of CuI and the flexible mixed N/S donor ligand 4-(2-(cyclohexylthio)ethoxy)pyridine (L). Single-crystal X-ray diffraction analyses reveal that these 1D CPs form sets of supramolecular isomers; 1 and 2 are based on Cu2I2 rhomboids, while 3-6 are based on cubane Cu4I4 clusters. Crystal-to-crystal transformations of CPs 1-6 were reversible under heat or in an appropriate solvent (acetonitrile, dichloromethane, chloroform, or benzene). In addition, crystal transformations between CPs 1 and 3 occurred through addition of L or CuI. Moreover, CPs 3-6 exhibited reversible guest exchange and crystal transformations on exposure to the vapor of volatile organic compounds and heat. Remarkably, a guest molecule was exchanged by other guest molecules in the vapor phase within very short times and without the use of acetonitrile as a solvent, which normally plays a key role in trapped solvent exchange experiments.