Triazoles and tetrazoles: Prime ligands to generate remarkable coordination materials

The building block modular approach that lies behind coordination polymers (CPs) and metal–organic frameworks (MOFs) results not only in a plethora of materials that can be obtained but also in a vast array of material properties that could be aimed at. Optical properties appear to be particularly predetermined by the character of individual structural units and by the intricate interplay between them. Indeed, the “design principles” shaping the optical properties of these materials seem to be well explored for luminescence and second-harmonic generation (SHG) phenomena; these have been covered in numerous previous reviews. Herein, we shine light on CPs and MOFs as optical media for state-of-the-art photonic phenomena such as multi-photon absorption, triplet–triplet annihilation (TTA) and stimulated emission. In the first part of this review we focus on the nonlinear optical (NLO) properties of CPs and MOFs, with a closer look at the two-photon absorption property. We discuss the scope of applicability of most commonly used measurement techniques (Z-scan and two-photon excited fluorescence (TPEF)) that can be applied for proper determination of the NLO properties of these materials; in particular, we suggest recommendations for their use, along with a discussion of the best reporting practices of NLO parameters. We also outline design principles, employing both intramolecular and intermolecular strategies, that are necessary for maximizing the NLO response. A review of recent literature on two-, three- and multi-photon absorption in CPs and MOFs is further supplemented with application-oriented processes such as two-photon 3D patterning and data storage. Additionally, we provide an overview of the latest achievements in the field of frequency doubling (SHG) and tripling (third-harmonic generation, THG) in these materials. Apart from nonlinear processes, in the next sections we also target the photonic properties of MOFs that benefit from their porosity, and resulting from this their ability to serve as containers for optically-active molecules. Thus, we survey dye@MOF composites as novel media in which efficient upconversion via triplet energy migration (TEM) occurs as well as materials for stimulated emission and multi-photon pumped lasing. Prospects for producing lasing as an intrinsic property of MOFs has also been discussed. Overall, further development of the optical processes highlighted herein should allow for realization of various photonic, data storage, biomedical and optoelectronic applications.

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Nonlinear optical properties, upconversion and lasing in metal–organic frameworks

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the functi...

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation.

A fluorescent ratiometric Hg2+ ion sensor RMS, based on a coumarin platform coupled with a tetraamide receptor, is presented. This sensor, employing the ICT mechanism, could be used to specifically detect Hg2+ ions in a neutral buffered water solution with an approximately 100-nm blue shift in emission spectra.

Detecting Hg2+ ions with an ICT fluorescent sensor molecule: remarkable emission spectra shift and unique selectivity.

Four novel cadmium−btx (btx = 1,4-bis(triazol-1-ylmethyl)benzene) coordination polymers [Cd(btx)2(NO3)2]n (1), [Cd(btx)2Cl2]n (2), [Cd(btx)(SO4)(H2O)2]n (3), and [Cd(btx)(S2O7)(H2O)]n (4) have been prepared by hydrothermal reaction (140 or 180 °C) and characterized. Both 1 and 2 have two-dimensional rhombohedral grid structures, 3 possesses a two-dimensional rectangular grid structure, and 4 displays a three-dimensional framework, which is formed by btx bridging parallel layers. To the author's best knowledge, polymer 4 is the first Cd(II) polymer in which the Cd(II) ion is eight-coordinated in a hexagonal bipyrimidal geometry. In addition, we studied the effects of temperature on the hydrothermal reaction system of btx and CdSO4 and found that different products can be obtained at different temperatures. Furthermore, polymer 3 possesses a very strong third-order NLO absorptive effect with an α2 value of 1.15 × 10-9 m W-1. Polymers 2−4 display strong fluorescent emissions in the solid state at room temper...

Hydrothermal Syntheses, Crystal Structures, and Characteristics of a Series of Cd-btx Coordination Polymers (btx = 1,4-Bis(triazol-1-ylmethyl)benzene)

Three novel coordination polymers [Pb(bbbm)2(NO3)2]n (bbbm = 1,1‘-(1,4-butanediyl)bis-1H-benzimidazole) 1, [Zn(bbbt)(NCS)2]n (bbbt = 1,1‘-(1,4-butanediyl)bis-1H-benzotriazole) 2, and [Zn(pbbt)(NCS)2]n (pbbt = 1,1‘-(1,3-propylene)bis-1H-benzotriazole) 3 were synthesized and structurally characterized. Polymer 1 exhibits a two-dimensional rhombohedral grid network structure, the dimensions of the grid are 14.274 × 14.274 A, and the diagonal-to-diagonal distances are 24.809 × 14.125 A. Polymer 2 possesses a concavo-convex chain structure different from those of the known one-dimensional polymers, which are linear chain, zigzag chain, helical chain, double-stranded chain, and ladder chain. Polymer 3 exhibits a one-dimensional zigzag chain structure, and these chains were packed as an ...ABAB... layered structure. The third-order nonlinear optical (NLO) properties of polymers 1, 2, and 3 were determined with a 7-ns pulsed laser at 532 nm. 1 shows strong third-order NLO absorptive and refractive properties, and...

Novel pb and zn coordination polymers: synthesis, molecular structures, and third-order nonlinear optical properties.

Three novel ferrocenyl complexes [Zn(4-PFA)2(NO3)2](H2O) (1), [Hg2(OAc)4(4-BPFA)2](CH3OH) (2), and [Cd2(OAc)4(4-BPFA)2] (3) (4-PFA = [(4-pyridylamino)carbonyl]ferrocene, 4-BPFA = 1,1‘-bis[(4-pyridylamino)carbonyl]ferrocene) were prepared, and complexes 1 and 2 were structurally characterized by means of X-ray single-crystal diffraction. In complex 1, the zinc(II) atom is coordinated at a distorted tetrahedral environment by two nitrogen atoms from two 4-PFA moieties and two oxygen atoms from two nitrate anions; [Zn(4-PFA)2(NO3)2] units are linked by hydrogen bonds N−H···O and O−H···O forming one-dimensional chains. Complex 2 is a tetranuclear macrocycle compound consisting of two 4-BPFA moieties and two Hg atoms; [Hg2(OAc)4(4-BPFA)2] units form 1-D chains by hydrogen bonds N−H···O as complex 1. Some complexes with 1,1‘-bisubstituted pyridine-containing ferrocene ligands have been described, but their crystal data are limited. Compound 2 is the first example of a macrocyclic pyridine-containing ferrocenyl ...

Gang Li

Papers

Novel pb and zn coordination polymers: synthesis, molecular structures, and third-order nonlinear optical properties.

Synthesis, crystal structures, and third-order nonlinear optical properties of a series of ferrocenyl organometallics.