Tetrazine chromophore-based metal-organic frameworks with unusual configurations: synthetic, structural, theoretical, fluorescent, and nonlinear optical studies

Chiral Wheel Anions of Copper(II)-Early Lanthanides(III) with High Optical-Limiting Properties

A new family of chiral wheel anions {CuII22LnIII4} (La, Ce, Pr, Nd and Sm) was obtained from aqueous solution by the use of tartrate anions. It provides a new perspective...

Interpenetrated Metal-Porphyrinic Framework for Enhanced Nonlinear Optical Limiting

Structural interpenetration in metal-organic frameworks (MOFs) significantly impacts on their properties and functionalities. However, understanding the interpenetration on third-order nonlinear optics (NLO) of MOFs have not been reported to date. Herein, we report two 3D porphyrinic MOFs, a 2-fold interpenetrated [Zn₂(TPyP)(AC)₂] (ZnTPyP-1) and a noninterpenetrated [Zn₃(TPyP)(H₂O)₂(C₂O₄)₂] (ZnTPyP-2), constructed from 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP(H₂)) and Zn(NO₃)₂ (AC = acetate, C₂O₄ = oxalate). ZnTPyP-1 achieves excellent optical limiting (OL) performance with a giant nonlinear absorption coefficient (3.61 × 10⁶ cm/GW) and large third-order susceptibility (7.73 × 10^-7 esu), which is much better than ZnTPyP-2 and other reported OL materials. The corresponding MOFs nanosheets are dispersed into a polydimethylsiloxane (PDMS) matrix to form highly transparent and flexible MOFs/PDMS glasses for practical OL application. In addition, the OL response optimized by adjusting the MOFs concentration in the PDMS matrix and the type of metalloporphyrin are discussed in the ZnTPyP-1 system. The theoretical calculation confirmed that the abundant π-π interaction from porphyrinic groups in the interpenetrated framework increased the electron delocalization/transfer and boosted the OL performance. This study opens a new avenue to enhance OL performance by the construction of interpenetrated structures and provides a new approach for the preparation of transparent and flexible MOF composites in nonlinear optical applications.

1,2,4,5-Tetrazine based ligands and complexes

One of the most intriguing nitrogen based aromatic heterocycles is 1,2,4,5-tetrazine or s-tetrazine (TTZ) thanks to its electron acceptor character and fluorescence properties and the possibilities of functionalization in the 3 and 6 positions allowing access to various ligands. In this review we focus on the two main families of TTZ based ligands, i.e. ditopic symmetric and monotopic non-symmetric, together with their metal complexes, with a special emphasis on their solid state structures and physical properties. After a description of the most representative complexes containing unsubstituted TTZ as a ligand, symmetric TTZ ligands and complexes derived thereof are discussed in the order: 3,6-bis(2-pyridyl)-tetrazine, 3,6-bis(3-pyridyl)-tetrazine, 3,6-bis(4-pyridyl)-tetrazine, 3,6-bis(2-pyrimidyl)-tetrazine, 3,6-bis(2-pyrazinyl)-tetrazine, 3,6-bis(monopicolylamine)-tetrazine, 3,6-bis(vanillin-hydrazinyl)-tetrazine and TTZ containing carboxylic acids. Remarkable results have been obtained in recent years for metal-organic frameworks and magnetic compounds in which magnetic coupling is enhanced when the tetrazine bridge is reduced to radical anions. Non-symmetric ligands, such as dipicolylamine-TTZ and monopicolylamine-TTZ, are comparatively more recent than the symmetric ones. They allow in principle the preparation of mononuclear complexes in a controlled manner, although binuclear complexes have been isolated as well. Moreover, in the monopicolylamine-TTZ-Cl ligand, deprotonation of the amine, thanks to the electron acceptor character of TTZ, afforded a negatively charged ligand equivalent of a guanidinate.

Auto-controlled fabrication of a metal-porphyrin framework thin film with tunable optical limiting effects

Metal-organic frameworks (MOFs) with third-order nonlinear optical (NLO) properties are still in their infancy but are very important. In this work, we first develop a layer by layer autoarm immersion method for preparing porphyrin-based MOF (PIZA-1) thin films with third-order NLO properties. By precisely controlling the thickness, the nonlinear absorption of PIZA-1 thin films can be switched continuously between reverse saturable absorption (RSA) and saturable absorption (SA) by using the Z-scan technique. In addition, the optical limiting effect could be further optimized by loading C₆₀ in the pores of the PIZA-1 thin film. These findings not only open a new route for the exploitation of third-order NLO thin film materials, but also offer an insightful understanding of porphyrin-based MOF thin films for future broad practical applications.

Auxiliary ligand-induced structural diversities of octacyanometalate-based heterobimetallic coordination polymers towards diverse magnetic properties

Three octacyanometalate-based bimetallic coordination polymers (CPs), {[μ₄-M^V(CN)₈][Co(DMF)₄]₂(ClO₄)}_n (M = W CP-1, Mo CP-2) and {[μ₄-W^IV(CN)₈]Co₂(azpy)₄}_n CP-3, were synthesized in the absence (for CPs 1 and 2) or presence (for CP-3) of auxiliary ligand 4,4'-azopyridine (azpy), respectively. CPs 1 and 2 exhibit the same three-dimensional (3D) polymeric cation frameworks with [ClO₄]^- as the counterions, while CP-3 displays a porous 3D framework in an unusual 2-nodal (4,6)-connected 4,6T155 topology with point symbol as {4²·6⁴}{4⁶·6⁴·7·8⁴}₂. Notably is that octacyanometalate [W^V(CN)₈]^3- has been reduced into [W^IV(CN)₈]^4- during the synthetic process of CP-3. The magnetic investigations indicate that CP-1 exhibits the typical ferromagnetic property due to the ferromagnetic coupling between W(v) and Co(ii) spin centers, while CP-3 displays the weak ferromagnetic interaction at low temperature, which is consistent with the valence change of W center in CP-3.

A thiazolo[5,4-d]thiazole-bridged porphyrin organic framework as a promising nonlinear optical material

We report a porous thiazolo[5,4-d]thiazole-bridged porphyrin organic framework, Por-TzTz-POF, with promising nonlinear optical (NLO) activity.

Coordination polymers built up from an s-tetrazine derived ligand and rare-earth ions: from a sequential dimensional expansion to organic-inorganic energy transfer

Coordination polymers were prepared from a luminescent s-tetrazine ligand (OTz) and various rare-earth ions. Both the radii of the Ln ions and the synthetic conditions (especially pH) drive the formation of the product, and three crystalline phases were finally identified. Using a two-step process, it was possible to increase the dimensionality of one of these compounds from 1-D (MIL-165) to 2-D (MIL-166). The luminescence properties of these coordination polymers were studied. Whereas for Ln = La, Pr, Eu, Tb, the emission characteristic of the s-tetrazine core was observed, such emission was not detected for Ln = Nd, while the emission typical for the Nd ion was present, due to energy transfer from the tetrazine ligand to the Nd³⁺ ion.

Network Formation via Anion Coordination: Crystal Structures Based on the Interplay of Non-Covalent Interactions

We describe the synthesis and the structural characterization of new H₂L(CF₃CO₂)₂ (1) and H₂L(Ph₂PO₄)₂ (2) compounds containing the diprotonated form (H₂L²⁺) of the tetrazine-based molecule 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine. X-ray diffraction (XRD) analysis of single crystals of these compounds showed that H₂L²⁺ displays similar binding properties toward both anions when salt bridge interactions are taken into account. Nevertheless, the different shapes, sizes and functionalities of trifluoroacetate and diphenyl phosphate anions define quite different organization patterns leading to the peculiar crystal lattices of 1 and 2. These three-dimensional (3D) architectures are self-assembled by a variety of non-covalent forces, among which prominent roles are played by fluorine–π (in 1) and anion–π (in 2) interactions.

Solvatochromism as a probe to observe the solvent exchange process in a 1-D porous coordination polymer with 1-D solvent accessible channels

A one-dimensional porous coordination polymer possessing pleochroic and solvatochromic properties produces an unexpected double V-shaped discolouration of the crystal upon solvent exchange with acetonitrile and nitromethane. Modelling shows that the origin of this effect is preferential sorption at two faces of the crystal.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

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 function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

Ammonium-crown ether supramolecular cation-templated assembly of an unprecedented heterobicluster-metal coordination polymer with enhanced NLO properties

An ammonium-crown ether host-guest supramolecular cation-templated synthetic methodology has been developed to construct a structurally unprecedented heterobicluster-metal coordination polymer (HCM-CP 1) based on tetranuclear clusters [WS4Cu3](+) with different connection environments, pentanuclear clusters [WS4Cu4](2+), and Cu(+) building metal ions. HCM-CP 1 exhibits enhanced NLO properties, which may be ascribed to the incorporation of diverse building cluster components.

Three Zn(ii)/Cd(ii)/Mn(ii) coordination polymers based on a 2-hydroxy-N-(1H-tetrazol-5-yl) benzamide ligand: structures, and magnetic and photoluminescence properties

Three transition metal complexes of the amide decorated tetrazolate are reported that include an interdigitated 3-D structure with 1-D channels.