Luminescent Coordination Polymers Based on Self-Assembled Cadmium Dipyrrin Complexes

Metal Coordination Effects on the Photophysics of Dipyrrinato Photosensitizers

Within this work, we review the metal coordination effect on the photophysics of metal dipyrrinato complexes. Dipyrrinato complexes are promising candidates in the search for alternative transition metal photosensitizers for application in photodynamic therapy (PDT). These complexes can be activated by irradiation with light of a specific wavelength, after which, cytotoxic reactive oxygen species (ROS) are generated. The metal coordination allows for the use of the heavy atom effect, which can enhance the triplet generation necessary for generation of ROS. Additionally, the flexibility of these complexes for metal ions, substitutions and ligands allows the possibility to tune their photophysical properties. A general overview of the mechanism of photodynamic therapy and the properties of the triplet photosensitizers is given, followed by further details of dipyrrinato complexes described in the literature that show relevance as photosensitizers for PDT. In particular, the photophysical properties of Re(I), Ru(II), Rh(III), Ir(III), Zn(II), Pd(II), Pt(II), Ni(II), Cu(II), Ga(III), In(III) and Al(III) dipyrrinato complexes are discussed. The potential for future development in the field of (dipyrrinato)metal complexes is addressed, and several new research topics are suggested throughout this work. We propose that significant advances could be made for heteroleptic bis(dipyrrinato)zinc(II) and homoleptic bis(dipyrrinato)palladium(II) complexes and their application as photosensitizers for PDT.

Tailored Inorganic-Organic Architectures via Metalloligands

This article discusses the design principles and strategies and the structural outcome of various supramolecular architectures constructed by utilizing well-defined coordination complexes as the metalloligands. We have included selected examples of metalloligands, offering either pyridyl or arylcarboxylic acid groups as the appended functional groups, for illustrating the construction of their supramolecular architectures. Both geometrical position and the number of the appended functional groups emerging from a metalloligand were found to critically regulate the structural aspects and dimensionality of the resultant material. The article concludes by delineating the structure-directing lessions as well as the potential applications of the metalloligand-based supramolecular architectures for the generation of next-level materials.

Synthesis, Structure, and Properties of Helical Bis-Cu(II) Complex of Linear Hexapyrrolic Ligand

The chemistry of metal helical complexes has attracted wide interest not only because of their resemblance with DNA structure but also due to their unique photophysical and chiroptical properties. Linear hexapyrrolic ligand 1 has been designed and synthesized using 3-pyrrolyl BODIPY as a key precursor. The reactivity of the appended pyrrole group of 3-pyrrolyl BODIPY was taken as an advantage to synthesize bis(3-pyrrolyl BODIPY) by treating 3-pyrrolyl BODIPY with 10 equiv of acetone in CHCl₃ under acid-catalyzed conditions and afforded bis(3-pyrrolyl BODIPY) 2 in 20% yield. Bis(3-pyrrolyl BODIPY) 2, in which two 3-pyrrolyl BODIPY units were connected via sp³ meso carbon, was very stable, and its identity was confirmed by HR-MS, NMR, and X-ray crystallographic analysis. The X-ray structure revealed that the 3-pyrrolyl BODIPY moieties in bis(3-pyrrolyl BODIPY) 2 remained almost planar and arranged at an angle of 98.4° with each other, leading to a V-shaped conformation. In the next step, bis(3-pyrrolyl BODIPY) 2 was treated with AlCl₃ in acetonitrile/methanol at reflux to afford hexapyrrolic ligand 1. Hexapyrrolic ligand 1 was treated with CuCl₂ in acetonitrile at room temp for 1 h followed by crystallization to afford helical bis-Cu(II) complex 1-Cu. Bis-Cu(II) complex 1-Cu was characterized and studied by HR-MS, X-ray crystallography, ESR, absorption, and DFT/TD-DFT techniques. The X-ray structure revealed that the bis-Cu(II) complex was a double-stranded bimetallic helicate and each Cu(II) ion was coordinated to four nitrogen atoms of two dipyrrin units from two hexapyrrolic ligands in a distorted tetrahedral geometry. The crystal packing diagram showed that the bis-Cu(II) complex formed as a racemic mixture containing both M and P isomers which was unable to isolate. The ESR spectrum of bis-Cu(II) complex 1-Cu indicated the presence of two noninteracting Cu(II) ions in slightly different coordination environments. DFT and TD-DFT studies were in agreement with the experimental observations of bis(3-pyrrolyl BODIPY) 2 complex and bis-Cu(II) complex 1-Cu.

Luminescence from open-shell, first-row transition metal dipyrrin complexes

Several first-row transition metal complexes of the 1,9-bis(2',4',6'-triphenylphenyl)-5-mesityl dipyrrinato ligand and its tetrahalogenated analogues have been synthesized and their luminescence spectra obtained. The protonated ligands, as well as the Li(i), Mn(ii), Cu(i), Cu(ii), and Zn(ii) chelates show appreciable luminescence, despite the paramagnetism of the Mn(ii) and Cu(ii) ions. Fluorescence quantum yields (ΦF) as high as 0.67 were observed for the zinc complex. Luminescence was partially quenched by the introduction of heavy halogens to the backbone of the ligand, as well as by the introduction of paramagnetic metal ions. Room-temperature, solution state phosphorescence was observed from the halogenated dipyrrinato lithium salts, as well as from the non-halogenated Mn(ii) complex.

Recent developments in dipyrrin based metal complexes: Self-assembled nanoarchitectures and materials applications

While dipyrrin-boron complexes (BODIPYs) and their derivatives have attracted much attention, dipyrrin-based metal complexes recently appeared as a novel luminescent material. So far, dipyrrin-metal complexes have been regarded as non-luminescent or weakly luminescent. Interestingly, introduction of steric hindrance at the meso-position and the development of heteroleptic complexes with proper frontier orbital ordering are two recent strategies that have been developed to improve their luminescent ability. Compared with BODIPYs, one of the distinctive advantages of dipyrrin-metal complexes is that they can form a series of self-assembled supramolecules and polymer assemblies via facile coordination reactions. In recent times, several supramolecular, coordination polymers and Metal-Organic Frameworks (MOFs) have been developed, [Formula: see text] by spontaneous coordination reactions between dipyrrin ligands and metal ions. As a novel luminescent material, dipyrrin-metal complexes have been applied in many fields. This review article summarizes recent developments in dipyrrin-metal complexes from the viewpoint of the improvement of luminescent ability, the formation of supramolecular and coordination polymers and their potential applications.

Functional Supramolecular Architectures of Dipyrrin Complexes

Dynamic formation of self-assemblies from molecular components is a useful and efficient way to produce molecular and supramolecular architectures with sophisticated functions. The labile coordination bond and dynamic covalent bond as a reversible bond have often been used to create a well-organized supramolecular self-assembly. In order to realize sophisticated novel functions of the supramolecular self-assemblies, dipyrrin complexes have recently been employed as a functional unit and incorporated into the supramolecular architectures because of their outstanding properties and functions such as a high photostability and strong light absorption/emission. This review article summarizes recent development in functional supramolecular architectures of the dipyrrin complexes produced by coordination to a metal ion and dynamic covalent bond formation. We first describe the synthesis and unique functions of a series of discrete supramolecular architectures: helicates, macrocycles, and cages. The polymeric supramolecular self-assemblies with 1D, 2D, and 3D structures are then introduced as a functional infinite supramolecular architecture.

Coordination nanosheets (CONASHs): strategies, structures and functions

Nanosheets, which are two-dimensional polymeric materials, remain among the most actively researched areas of chemistry and physics this decade. Generally, nanosheets are inorganic materials created from bulk crystalline layered materials and have fascinating properties and functionalities. An emerging alternative is molecule-based nanosheets containing organic molecular components. Molecule-based nanosheets offer great diversity because their molecular, ionic, and atomic constituents can be selected and combined to produce a wide variety of nanosheets. The present article focuses on coordination nanosheets (CONASHs), a class of molecule-based nanosheets comprising organic ligand molecules and metal ions/atoms in a framework linked with coordination bonds. Following the Introduction, Section 2 describes CONASHs, including their definition, design, synthetic procedures, and characterisation techniques. Section 3 introduces various examples of CONASHs, and Section 4 explores their functionality and possible applications. Section 5 describes an outlook for the research field of CONASHs.

Symmetrical and dissymmetrical 2,2′-bis-dipyrrin ligands and Zn(ii) binuclear helicates

A series of amide functionalized symmetrical and dissymmetrical 2,2′-bis-dipyrrin ligands has been prepared and characterized and their assembly with Zn(ii) towards the formation of binuclear helicates has been investigated.

Synthesis of an F-BODIPY [2]catenane using the chemistry of bis(dipyrrinato)metal complexes

Towards highly fluorescent BODIPY based mechanically interlocked molecules via the chemistry of dipyrrins.

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State

This Communication reports the first observation of solid-state photoluminescence in bis(dipyrrinato)zinc(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their meso-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state.

Copper(ii) complexes with phosphorylated 1,10-phenanthrolines: from molecules to infinite supramolecular arrays

Supramolecular architectures based on copper(ii) complexes with diethoxyphosphoryl substituted 1,10-phenanthrolines are reported.

Dipyrrin complex assisted in situ synthesis of ultra-small gold nanoparticles decorated on a partially reduced graphene oxide nanocomposite for efficient catalytic reduction of Cr(vi) to Cr(iii)

Applicability of a novel heteroleptic dipyrrin complex exhibiting dual functionality (reducing and capping agent) in rapid synthesis of small sized AuNPs has been described.

Distortion Pathways of Transition Metal Coordination Polyhedra Induced by Chelating Topology

A continuous shape measures analysis of the coordination polyhedra of a host of transition metal complexes with bi- and multidentate ligands discloses the distortion pathway associated with each particular topology of the chelate rings formed. The basic parameter that controls the degree of distortion is the metal-donor atom bond distance that induces nonideal bond angles due to the rigidity of the ligands. Thus, the degree of distortion within each family of complexes depends on the atomic size, on which the high- or low-spin state has a large effect. Special attention is therefore paid to several spin-crossover systems and to the enhanced distortions that go along with the transition from low- to high-spin state affected by temperature, light, or pressure. Several families of complexes show deviations from the expected distortion pathways in the high-spin state that can be associated to the onset of intermolecular interactions such as secondary coordination of counterions or solvent molecules. Also, significant displacement of counterions in an extended solid may result from the changes in metal-ligand bond distances when ligands are involved in intermolecular hydrogen bonding.

On Zn(II) 2,2'-bisdipyrrin circular helicates

Coordination of two 2,2'-bisdipyrrin ligands, bearing methyl ester or methylthioether peripheral groups, with Zn(II) cations leads not only to the formation of the expected linear helicates but also concomitantly to novel tri- and tetra-nuclear circular species that have been isolated and fully characterized in solution and by X-ray diffraction.

Bis(dipyrrinato)metal(ii) coordination polymers: crystallization, exfoliation into single wires, and electric conversion ability

The titled coordination polymers feature crystallization, single wire exfoliation, processability, and applicability to photoelectric and thermoelectric conversion systems.

One-dimensional coordination polymers (1D-CPs) tend either to dissociate into constitutive ligands and metals readily in solution, or to aggregate randomly and amorphously, which prevents them from widespread application. In the present research, 1D-CPs comprising bridging dipyrrin ligands and divalent metal ions (Zn²⁺, Ni²⁺, and Cu²⁺) are synthesized. A liquid/liquid interfacial reaction gives rise to single crystals suitable for X-ray diffraction analysis: A dichloromethane solution of the ligand is layered with aqueous metal(ii) acetate, such that the coordination reaction proceeds at the liquid/liquid interface. Isolated single fibers of the zinc coordination polymer may be exfoliated from the single crystal or bulk solid upon ultrasonication. Atomic force microscopy (AFM) detects the isolated fibers with lengths of more than several μm. The exfoliated 1D-CP wires feature good processability, realizing a conjugate with single-wall carbon nanotubes (SWCNTs), and a thin film on a transparent SnO₂ electrode. The processed materials show electric conversion ability: For example, the modified SnO₂ electrode serves as a photoanode for a photoelectric conversion system. The designability and tunability of the present 1D-CPs is demonstrated by a ligand modification, affording a luminescent property and an extension of the photoelectric conversion response to longer wavelengths.

Assembly, disassembly, and reassembly: conversion of homometallic coordination networks into mixed metal-organic frameworks

A strategy for the conversion of homometallic coordination networks into mixed metal-organic frameworks (MM'MOFs) is proposed. Ni(II) complexes of dipyrrin (dpm) ligands bearing peripheral pyridyl or imidazolyl units have been shown to self-assemble into coordination polymers with the metal cation in an octahedral environment coordinated to two bis-pyrrolic chelates and two neutral monodentate coordinating units such as pyridyl or imidazolyl moieties. Taking advantage of the chelate effect, the two monodentate units may be replaced by a diimine ligand leading to the disassembly of the networks by the formation of discrete soluble complexes. The latter can be employed as metallatectons for the construction of heterometallic architectures upon reaction with a secondary metal salt. This approach was applied using either 1,10-phenanthroline (phen) or 2,2'-bipyrimidine (bpm) as chelates leading to a series of mono- and binuclear metallatectons of the (phen)Ni(dpm)2 and (bpm)[Ni(dpm)2]2 type. Subsequent assembly with CdCl2 afforded either interpenetrated 2D grid-type architectures or 3D MM'MOFs.

Synthesis, crystal structure, photoluminescence, and DFT studies of bis(1,10-phenanthroline)di(κ(2)OO' nitrato)cadmium(II) [Cd(phen)2(NO3)2]

A cadmium 1,10-phenanthroline complex, [Cd(phen)2(NO3)2] has been synthesized by and its crystal structure determined. The compound is monoclinic, C2/c, a=11.5008(2), b=15.3523(2), c=13.2767(2)Å, β=103.610(2), Z=4. The compound is monomeric with a octacoordinate cadmium ion bonded to two bidentate 1,10-phenanthroline molecules and two bidentate nitrate units. The metal ion is bis-chelated by two N-heterocycles as well as by two nitrate ions in a distorted dodecahedral CdN4O4 coordination environment. The complex is thermally stable up to 110°C. Photophysical investigation reveals that complex is luminescent in the solid state. The molecular geometry, harmonic vibrational frequencies and bonding features of complex [Cd(phen)2(NO3)2] in the ground-state have been calculated by using the density functional B3LYP method with 3-21G (d, p) as higher basis set. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Finally the calculation results were applied to simulate infrared spectrum of the title compound which show good agreement with observed spectrum.

Asymmetric dinuclear bis(dipyrrinato)zinc(ii) complexes: broad absorption and unidirectional quantitative exciton transmission

Asymmetric, heteroleptic dinuclear bis(dipyrrinato)zinc(ii) complexes convey excitons quantitatively and rapidly across their structure from one end to the other.