Triple-Stranded Helicates of Zinc(II) and Cadmium(II) Involving a New Redox-Active Multiring Nitrogenous Heterocyclic Ligand: Synthesis, Structure, and Electrochemical and Photophysical Properties

Imidazo[1,2-a]pyridine and Imidazo[1,5-a]pyridine: Electron Donor Groups in the Design of D-π-A Dyes

This work investigates the electron-donating capabilities of two 10-π electron nitrogen bridgehead bicyclic [5,6]-fused ring systems, imidazo[1,2-a]pyridine and imidazo[1,5-a]pyridine rings. Eight compounds with varying positions of electron-withdrawing moieties (TCF or DCI) coupled to the imidazopyridine ring were synthesized and studied. DCI-containing compounds (Ib-IVb) exhibited a purely dipolar nature with broad absorption bands, weak fluorescence, large Stokes shifts, and strong solvatochromism. In contrast, TCF-containing compounds (Ia-IVa) demonstrated diverse properties. Imidazo[1,2-a]pyridine derivatives Ia and IIa were purely dipolar, while imidazo[1,5-a]pyridine derivatives IIIa and IVa displayed a cyanine-like character with intense absorption and higher quantum yields of emission. The observed gradual red shift in optical properties with changing electron-donor groups (IIb < Ib < IIIb < IVb) and (IIa < Ia < IIIa < IVa) underscores the stronger electron-donor character of imidazo[1,5-a]pyridine compared to that of imidazo[1,2-a]pyridine. Furthermore, crystalline powders of imidazo[1,2-a]pyridine derivatives exhibited fluorescence despite minimal emission in solution. Two compounds (Ib and IVa) were successfully formulated into nanoparticles for potential in vivo imaging applications in zebrafish embryos.

Imidazopyridine Family: Versatile and Promising Heterocyclic Skeletons for Different Applications

In recent years, there has been increasing attention focused on various products belonging to the imidazopyridine family; this class of heterocyclic compounds shows unique chemical structure, versatile optical properties, and diverse biological attributes. The broad family of imidazopyridines encompasses different heterocycles, each with its own specific properties and distinct characteristics, making all of them promising for various application fields. In general, this useful category of aromatic heterocycles holds significant promise across various research domains, spanning from material science to pharmaceuticals. The various cores belonging to the imidazopyridine family exhibit unique properties, such as serving as emitters in imaging, ligands for transition metals, showing reversible electrochemical properties, and demonstrating biological activity. Recently, numerous noteworthy advancements have emerged in different technological fields, including optoelectronic devices, sensors, energy conversion, medical applications, and shining emitters for imaging and microscopy. This review intends to provide a state-of-the-art overview of this framework from 1955 to the present day, unveiling different aspects of various applications. This extensive literature survey may guide chemists and researchers in the quest for novel imidazopyridine compounds with enhanced properties and efficiency in different uses.

Tetracoordinated 15-Electron Ruthenium(I) in a Discrete Triruthenium Framework

This paper highlights the unique case of a tetracoordinated Ru(I) (15-electron) component in a structurally characterized discrete triruthenium setup, [(acac)2RuIIIL1(μ-RuI)L1RuII (acac)2](ClO4)2 ([3](ClO4)2, where acac = acetylacetonate; S = 1), which was formed along with the monomeric [(acac)2RuIII(L1)] ([1]ClO4; S = 1/2) and dimeric [{(acac)2RuIII}2(μ-L1)](ClO4)2 ([2](ClO4)2; S = 1) counterparts upon interaction of {Ru(acac)2} and L1 = 3,3'-dipyridin-2-yl-1,1'-bis(imidazo[1,5-a]pyridinyl).

Progress in the Development of Imidazopyridine-Based Fluorescent Probes for Diverse Applications

Different classes of Imidazopyridine i.e., Imidazo[1,2-a]pyridine, Imidazo[1,5-a] pyridine, Imidazo[4,5-b]pyridine, have shown versatile applications in various fields. In this review, we have concisely presented the usefulness of the fluorescent property of imidazopyridine in different fields such as imaging tools, optoelectronics, metal ion detection, etc. Fluorescence mechanisms such as excited state intramolecular proton transfer, photoinduced electron transfer, fluorescence resonance energy transfer, intramolecular charge transfer, etc. are incorporated in the designed fluorophore to make it for fluorescent applications. It has been widely employed for metal ion detection, where selective metal ion detection is possible with triazole-attached imidazopyridine, β-carboline imidazopyridine hybrid, quinoline conjugated imidazopyridine, and many more. Also, other popular applications involve organic light emitting diodes and cell imaging. This review shed a light on recent development in this area especially focusing on the optical properties of the molecules with their usage which would be helpful in designing application-based new imidazopyridine derivatives.

FeII, CoII and NiII complexes based on 1-chloro-3-(pyridin-2-yl)imidazo[1,5-a]pyridine: synthesis, structures, single-molecule magnetic and electrocatalytic properties

Three complexes [Fe2(L)2Cl4] (1), [Co2(L)2Cl4] (2) and [Ni(L)2Cl2]·CH2Cl2 (3) were synthesized and characterized. Complex 1 exhibits a slow magnetic relaxation behaviour. Complexes 1–3 are catalytically active toward the OER.

Driving the Emission Towards Blue by Controlling the HOMO-LUMO Energy Gap in BF2 -Functionalized 2-(Imidazo[1,5-a]pyridin-3-yl)phenols

Several boron compounds with 2-(imidazo[1,5-a]pyridin-3-yl)phenols, differentiated by the nature of the substituent (R) in the para position of the hydroxy group, have been synthesized and thoroughly characterized both in solution (1 H, 13 C, 11 B, 19 F NMR) and in the solid state (X-ray). All derivatives displayed attractive photophysical properties like very high Stokes shift, high fluorescence quantum yields and a good photostability in solution. Time-Dependent Density Functional Theory (TD-DFT) calculations allowed to define the main electronic transitions as intra ligand transitions (1 ILT), which was corroborated by the Natural Transition Orbitals (NTOs) shapes. The HOMO-LUMO energy gap was correlated to the electronic properties of the substituent R on the phenolic ring, as quantified by its σp Hammett constant.

Synthesis and characterization of new Pd(ii) and Pt(ii) complexes with 3-substituted 1-(2-pyridyl)imidazo[1,5-a]pyridine ligands

Several palladium(ii) and platinum(ii) complexes (1-20) of general formula [M(Lⁿ)(X)(Y)] [M = Pd, X = Y = Cl (1-Cl-4-Cl), X = Y = OAc (1-OAc-4-OAc); M = Pt: X = Y = Cl (5-8); M = Pd, X = Cl, Y = CH₃ (9-12); M = Pt, X = Cl, Y = CH₃ (13-16) or X = Y = CH₃ (17-20); n = 1-4] have been synthesized by reaction of different Pd(ii) and Pt(ii) derivatives with various 3-substituted 1-(2-pyridyl)-imidazo[1,5-a]pyridines; i.e.Lⁿ = 1-(2-pyridyl)-3-arylimidazo[1,5-a]pyridine (aryl = Phenyl, L¹; 2-o-Tolyl, L²; Mesityl, L³) and 1-(2-pyridyl)-3-benzylimidazo[1,5-a]pyridine (L⁴). Detailed spectroscopic investigation (including IR, mono- and bi-dimensional ¹H NMR) and elemental analysis has been performed for all these species, allowing their complete characterization. Lⁿ act as N,N-bidentate ligands and coordinate the metal centers in a chelate fashion through the pyridyl (N_py) and the pyridine-like nitrogen atom of the imidazo[1,5-a]pyridine group (N_im). The X-ray structural analysis performed on two of Pd(ii) and three Pt(ii) complexes, namely [Pd(L²)(CH₃)Cl] (10), [Pd(L³)(CH₃)Cl] (11) and [Pt(L¹)Cl₂] (5), [Pt(L⁴)Cl₂] (8), [Pt(L²)(CH₃)Cl] (14) confirmed the spectroscopic and analytical data. Finally DFT studies unveiled the structural reasons behind the inertia of the synthesised compounds toward metalation, identified as the higher angle steric strain in comparison with the analogous bipyridine complexes.

Diversifying the luminescence of phenanthro-diimine ligands in zinc complexes

Strongly blue fluorescent 1-phenyl-2-(pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (L1) is a facile block for the construction of multichromophore organic molecules, and simultaneously serves as a chelating diimine ligand.

Imidazo[1,5-a]pyridine derivatives: useful, luminescent and versatile scaffolds for different applications

In the last few years, imidazo[1,5-a]pyridine nuclei and derivatives have attracted growing attention due to their unique chemical structure and versatility, optical behaviours, and biological properties.

Coordination polymers of a multipyridyl and pyrazolyl ligand with conformational flexibility: syntheses, structures and luminescence

Eight novel coordination polymers were obtained by the coordination of a multipyridyl and pyrazolyl ligand, which shows rich conformational changes.

Syntheses, crystal structure and luminescent properties of cadmium complexes based on 2,6-bis(1-phenylbenzimidazol-2-yl)pyridine

Two cadmium complexes, Cd(bpbp)Cl(2) (complex 1) and [Cd(bpbp)(2)](ClO(4))(2) (complex 2), based on 2,6-bis(1-phenylbenzimidazol-2-yl)pyridine (bpbp), were synthesized and characterized by X-ray single crystal structure analyses. For complex 1: crystal system, monoclinic, space group, C2/c, a=27.427(3)Å, b=13.4495(15)Å, c=14.8381(17)Å, β=106.635(2)°, V=5244.4(10)Å(3), Z=8. It is a neutral complex. The Cd(II) ion distorted trigonal bipyramidal geometry is five-coordinated by three nitrogen atoms from ligand (bpbp) and two chlorine ions. For complex 2: crystal system, triclinic, space group, P-1, a=13.4791(15)Å, b=13.8506(16)Å, c=16.5839(19)Å, α=94.202(2)°, β=106.948(2)°, γ=94.872(2)°, V=2935.3(6)Å(3), Z=2. It is an ionic complex. The Cd(II) ion octahedral geometry is six-coordinated by six nitrogen atoms from two ligand (bpbp). Both complexes emit blue luminescence with emission peaks at 420 and 430 nm in solid state and with emission peaks at 415 and 425 nm in DMF solution. In complex 1 absorption spectra, there is not only the free ligand absorption peak at 310 nm, but also shows strong Cd-Cl charge transfer peak at 350 nm in DMF solution.