Preparation and characterization of graphitic carbon nitride through pyrolysis of melamine

Graphitic carbon nitride (g-C₃N₄) has been synthesized via a two-step pyrolysis of melamine (C₃H₆N₆) at 800°C for 2 h under vacuum conditions. X-ray diffraction (XRD) patterns strongly indicate that the synthesized sample is g-C₃N₄. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) morphologies indicate that the product is mainly composed of graphitic carbon nitride. The stoichiometric ratio of C:N is determined to be 0.72 by elemental analysis (EA). Chemical bonding of the sample has been investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Electron energy loss spectroscopy (EELS) verifies the bonding state between carbon and nitrogen atoms. Optical properties of the g-C₃N₄ were investigated by PL (photoluminescence) measurements and UV–Vis (ultraviolet–visible) absorption spectra. We suppose its luminescent properties may have potential application as component of optical nanoscale devices. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were also performed.

Iridium(III) N-heterocyclic carbene complexes: an experimental and theoretical study of structural, spectroscopic, electrochemical and electrogenerated chemiluminescence properties

Four cationic heteroleptic iridium(III) complexes have been prepared from methyl- or benzyl-substituted chelating imidazolylidene or benzimidazolylidene ligands using a Ag(I) transmetallation protocol. The synthesised iridium(III) complexes were characterised by elemental analysis, (1)H and (13)C NMR spectroscopy and the molecular structures for three complexes were determined by single crystal X-ray diffraction. A combined theoretical and experimental investigation into the spectroscopic and electrochemical properties of the series was performed in order to gain understanding into the factors influencing photoluminescence and electrochemiluminescence efficiency for these complexes, with the results compared with those of similar NHC complexes of iridium and ruthenium. The N^C coordination mode in these complexes is thought to stabilise thermally accessible non-emissive states relative to the case with analogous complexes with C^C coordinated NHC ligands, resulting in low quantum yields. As a result of this and the instability of the oxidised and reduced forms of the complexes, the electrogenerated chemiluminescence intensities for the compounds are also low, despite favourable energetics. These studies provide valuable insights into the factors that must be considered when designing new NHC-based luminescent complexes.

Bimodal magneto-luminescent dysprosium (DyIII)-potassium (KI)-oxalate framework: magnetic switchability with high anisotropic barrier and solvent sensing

We report synthesis, characterization, and properties of a multifunctional oxalate framework, {KDy(C₂O₄)₂(H₂O)₄}_n (1) (C₂O₄^2- = oxalate dianion) composed of two absolutely different metal ions in terms of their size, charge, and electronic configuration. Dehydrated framework (1′) exhibits permanent porosity and interesting solvent (H₂O, MeOH, CH₃CN, and EtOH) vapor sorption characteristics based on specific interactions with unsaturated alkali metal sites on the pore surface. Compound 1 shows solvent responsive bimodal magnetic and luminescence properties related to the DyIII center. Compound 1 exhibits reversible ferromagnetic to antiferromagnetric phase transition upon dehydration and rehydration, hitherto unknown for any lanthanide based coordination polymer or metal-organic frameworks. Both the compounds 1 and 1′ exhibit slow magnetic relaxation with very high anisotropic barrier (417 ± 9 K for 1 and 418 ± 7 K for 1′) which has been ascribed to the single ion magnetic anisotropy of the Dy^III centers. Nevertheless, compound 1 shows a metal based luminescence property in the visible region and H₂O molecules exhibit the strongest quenching effect compared to other solvents MeOH, MeCN, and EtOH, evoking 1′ as a potential H₂O sensor.