The term nonlinear optics (NLO) was coined to describe the nonlinear relationship between dielectric polarization P and electric field E in optical media. NLO is a cornerstone of the emerging field of photonics, in which photons instead of electrons are used for signal transmission and processing. The vision of photonic signal transmission, processing, and storage has attracted a great deal of attention from both the engineering and the scientific communities because of its great impact in many of the existing and future information technologies. The first step toward realization of these revolutionary technologies is to develop tools to manipulate photons. For example, it is desirable to develop materials with the ability to alter the frequency of light, to amplify light signal, and to modulate light intensity or phase factors. NLO phenomena can be the key to achieving these important functions. One of the most common NLO behaviors is second-harmonic generation (SHG), in which a NLO material mediates the “adding-up” of two photons to form a new one with twice the frequency. The SHGphenomenonwas first demonstrated by Franken et al. in 1961. In their pioneering work, a laser beam with a wavelength of 694.2 nm was irradiated through a quartz crystal and an output ultraviolet radiation with a wavelength of 347.1 nm (double frequency) was detected. After this discovery, numerous nonlinear optical phenomena have been studied and a number of NLO-active materials have been developed. Second-harmonic generation can be quantitatively described by the second-order nonlinear optical susceptibility χ, a third-rank tensor with 27 components. The tensor elements are related to each other tomeet the requirements of both inherent and structural symmetries, which greatly reduces the number of independent components of the susceptibility tensor. Only crystals in noncentrosymmetric crystal classes can have nonvanishing χ. Moreover, for material crystallizing in the noncentrosymmetric 422, 622, and 432 crystal classes, the second-order NLO response might also vanish due to structural symmetry as well as Kleinman’s symmetry. Many inorganic compounds crystallize in noncentrosymmetric space groups and have been found to be SHG active. Some important examples are potassium dihydrogen phosphate (KDP = KH2PO4), lithium niobate (LiNbO3), and barium sodium niobate (Ba2NaNb5O15). 7 New inorganic compounds have been explored for NLO applications including but not limited to metal borates 12 and metal oxides. Recent structural studies on the inorganic systems have led to a better understanding of crystal growth/packing, paving the way for potentially manipulating their crystallization tendency to form noncentrosymmetric structures. Since the 1970s molecular NLO materials, including organic, organometallic, and inorganic complexes, have been of increasing interest to synthetic chemists. 19 The existing library of organic compounds was first screened, and the urea crystal has become a SHG standard because of its high SHG efficiency and usual availability. In a microscopic view, the second-order NLO susceptibility χ is related to the first hyperpolarizability β of a molecule. According to the classical two-level model, β is enhanced by a large transition moment and a large dipole moment difference between the ground and the charge transfer excited state. A donor acceptor type of molecule often possesses both a large transition moment and a large excited state dipole moment. As a result, most of the organic SHG chromophors belong to this category. However, most of the molecules with large β values also possess a large dipole moment, which induces formation of centrosymmetric assemblies of molecules due to dipole dipole interactions. One of the methods to avoid the centrosymmetric alignment of molecular dipoles is to trap them inside the channels of asymmetric porous host structures. 28 Other methods include formation of poled polymers in which the required asymmetry is imposed by the external electric field 35 and the Langmuir Blodgett (LB)

Rational synthesis of noncentrosymmetric metal-organic frameworks for second-order nonlinear optics.

Four novel highly connected metal–organic frameworks (MOFs) based on d10 metals and triangular ligands, namely, [Ag7(4,4′-tmbpt)(HL)2(L)(H2O)] (1), [NaCd3(4,4′-tmbpt)(L)2(OH)]·H2O (2), [Cd3(3,3′-tmbpt)2(L)2(H2O)2]·3.5H2O (3), and [Cd3(3,4′-tmbpt)2(L)2(H2O)]·1.5H2O (4) (H3L = 5-(4-carboxybenzyloxy)isophthalic acid, 4,4′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(4-pyridyl)-1,2,4-triazole, 3,3′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(3-pyridyl)-1,2,4-triazole, and 3,4′-tmbpt = 1-((1H-1,2,4-triazol-1-yl)methyl)-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole) have been synthesized under hydrothermal conditions. Compound 1 features a three-dimensional (3D) (3,12)-connected net based on heptanuclear [Ag7(COO)7] units. Compound 2 displays a 3D (3,4,10)-connected net constructed by tetranuclear [NaCd3(μ3-OH)(COO)5]+ units. Compound 3 exhibits a 3D (3,4,8)-connected net based on binuclear [Cd2(COO)2] units. Compound 4 is a 3D binodal (3,9)-connected framework constructed by trinuclear [Cd3(COO)4] unit...

A Series of Highly Connected Metal–Organic Frameworks Based on Triangular Ligands and d10 Metals: Syntheses, Structures, Photoluminescence, and Photocatalysis

Using bis-pyridyl-bis-amide ligands N,N′-bis-(4-pyridyl)phthalamide (L1), N,N′-bis-(4-pyridyl)iso -phthalamide (L2), hexanedioic acid bis-pyridin-4-ylamide (L3), and carboxylates, six metal(II) complexes formulated as Cd2(1,4-chdc)(L1)2·4H2O (1,4-H2chdc = 1,4-cyclohexanedicarboxylic acid) (1), Cd2(L1)2(in)4·3DMF (Hin = isonicotinic acid) (2), Zn(L1)(1,4-bdc) (1,4-H2bdc = 1,4-benzenedicarboxylic acid) (3), Cd(L2)(1,4-chdc) (4), Zn2(L2)2(tdc)2·DMF (H2tdc = thiophene-2,5-dicarboxylic acid) (5), and Zn(2,6-ndc)0.5(L3)0.5(SO4)·(CH3NHCH3) (2,6-H2ndc = 2,6-naphthalene- dicarboxylic acid) (6) have been hydro(solvo)thermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 is a uninodal 6-connected noninterpenetrated three-dimensional (3D) network with {44.610.8}-mab topology, complex 2 exhibits a uninodal 6-connected 2-fold interpenetrated 3D framework with {412.63}-pcu topology, complex 3 shows a uninodal 8-fold interpenetrated 3D diamondoid framework, complexes 4 and 5 p...

Metal(II) Coordination Polymers Derived from Bis-pyridyl-bis-amide Ligands and Carboxylates: Syntheses, Topological Structures, and Photoluminescence Properties

Seven new Zn(II) metal−organic frameworks [Zn(tib)2(H2O)](ClO4)2 (1), [Zn4(tib)2(PBDA)3(OH)2]·4H2O (2), [Zn(tib)(HPBDA)]ClO4 (3), [Zn2(tib)(PBDA)Cl2]·2H2O (4), [Zn4(tib)2(PBDA)3Cl2] (5), [Zn2(tib)2(PBDA)](NO3)2·2H2O (6), and [Zn2(tib)(PBDA)I2]·2H2O (7) [tib = 1,3,5-tris(1-imidazolyl)benzene, H2PBDA = p-benzenedicarboxylic acid] have been prepared and characterized by elemental, IR, thermogravimetric and X-ray diffraction analyses. Complexes 1 and 4 are two-dimensional (2D) networks with different topologies, which are further linked together to three-dimensional (3D) frameworks by hydrogen bonds. For 3, partial deprotonated HPBDA− is terminally coordinating to Zn(II) to form a 2D network. Complexes 2, 5, and 7 are 2-fold interpenetrated 3D frameworks, while 6 has a self-penetrating 3D structure. The influences of reaction temperature and counteranion on the structures of the complexes are discussed. The photoluminescence and nonlinear optical properties are investigated.

Interpenetrating and Self-Penetrating Zinc(II) Complexes with Rigid Tripodal Imidazole-Containing Ligand and Benzenedicarboxylate

Aliphatic and aromatic carboxylate divalent metal coordination polymers incorporating the kinked and hydrogen-bonding capable tethering ligand 4,4′-dipyridylamine

A new multicarboxylate ligand, 3,5-bis-oxyacetate-benzoic acid (H3BOABA), was designed and introduced to construct novel metal−organic framework materials with potential luminescent properties. Fou...

Syntheses, Structures, and Photoluminescence of Four d10 Metal−Organic Frameworks Constructed from 3,5-Bis-oxyacetate-benzoic Acid

Highly thermal stable zinc complex with unusual (4,8)-connected topology

The absorption spectra and frequency-dependent polarizabilities of Si n ( n  = 3–10) clusters have been calculated using time-dependent density functional theory (TDDFT) with 6-311+G ∗ basis set and frequency-dependent coupled perturbed Hartree–Fock (CPHF) method within DFT/6-311+G ∗ level, respectively. Four hybrid functionals (B3LYP, B3P86, B3PW91 and BHandHLYP) have been used to calculate the dynamic polarizabilities. With the input photon energy ( E inp ) ranging from 0.0 to 1.1 eV, several behaviors of the static polarizabilities hold for the dynamic values. The polarizabilities of all considered clusters exhibit the obvious anisotropic behavior and the near-resonance of E inp enhances the anisotropic behavior. The electronic origin of resonant polarizabilities of Si 3 and Si 4 clusters has been investigated using sum-over-states (SOS) method. The electronic transitions of π →  σ and σ →  n make a significant contribution to the dynamic polarizabilities of Si 3 and Si 4 cluster at E inp  = 1.612 and 1.488 eV, respectively.

Yi-Hang Wen

Papers

Syntheses, Structures, and Photoluminescence of Four d10 Metal−Organic Frameworks Constructed from 3,5-Bis-oxyacetate-benzoic Acid

Highly thermal stable zinc complex with unusual (4,8)-connected topology

Absorption spectra and frequency-dependent polarizabilities of small silicon clusters: A density functional study

Unusual 2D assembly of the paddle wheel Cd2(COO)4 units in a luminescent complex

Dynamic second-order hyperpolarizabilities of Si3 and Si4 clusters using coupled cluster cubic response theory