Transitions In Visible Region Research Articles

Synthesis, structural characterization, opto-electrical properties of Ir(III) complexes with imidazolium-based carbene ligands

A series of Ir(III) complexes with N–heterocyclic carbenes (NHC) ligands (1–3) were synthesized and characterized. The opto-electrical properties of these complexes were investigated spectroscopically, electrochemically and theoretically. All complexes exhibit ligand-based 1π,π* transitions in the UV region, 1MLCT absorption in the UV region, and weak low energy 3π, π* transition in visible region. These complexes all exhibit blue phosphorescence at both room temperature and 77K, which is dominated by 3π,π* character. DFT calculation results indicate their lowest unoccupied molecular orbitals (LUMO) from −0.47 to −0.33eV and the highest occupied molecular orbitals (HOMO) from −4.97 to −5.33eV. The opto-electrical properties can be influenced drastically by NHC ligands, which would be useful for rational design of optical functional materials.

Opto-structural and electrical properties of chemically grown Ga doped MoBi2Se5 thin films

An arrested precipitation route was developed to obtain gallium doped MoBi2Se5 thin films on substrate support. High purity organometallic complexes of Mo–triethanolamine (Mo–TEA), Bi–triethanolamine (Bi–TEA), Ga–triethanolamine (Ga–TEA) allow to react with sodium selenosulphite (Na2SeSO3) in the presence of sodium dithionite (Na2S2O4) as a reducing agent in an aqueous alkaline reaction bath. As deposited thin films were characterized by X-ray diffraction, which reveals that material is nanocrystalline with mixed phases of rhombohedral (Bi2Se3)-hexagonal (MoSe2)-hexagonal (GaSe) structures. Scanning electron micrographs show the grain of granular morphology decreases with increase in Ga concentration. Energy dispersive x-ray analysis shows presence of Mo, Bi, Ga and Se elements in stoichiometric ratio confirms the chemical formula MoBiGaSe5. Optical absorbance of the films show direct allowed transition in visible region having band gap energy in the range of 1.30–1.47 eV. Thermoelectric power and electrical conductivity measurements have been carried out for thin film samples in the temperature range 300–500 K and results revealed that n-type semiconducting behavior. It is interesting to note that Ga doping in MoBi2Se5 changes n to p type conductivity.

The kinetics and mechanism of the substitution reactions of the aquapentacyanoruthenate(II) ion with naphthalene‐substituted ligands in aqueous medium

AbstractThe kinetics and mechanism of substitution reaction of [Ru(CN)5H2O]3− anion with two naphthalene‐substituted ligands viz. Ln = nitroso‐R‐salt (NRS) and α‐nitroso‐β‐naphthol (αNβN) have been studied spectrophotometrically by monitoring an increase in absorbance at λmax = 525 nm corresponding to metal to ligand charge transfer (MLCT) transitions due to formation of substituted [Ru(CN)5L]n−3 as a function of pH, ionic strength, temperature, a wide range of ligands concentration, and [Ru(CN)5H2O3−] under pseudo‐first‐order conditions. The experimental observation suggests that [Ru(CN)5H2O]3− ion interacts with both ligands, which finally get converted into corresponding, [Ru(CN)5L]n−3 complexes as a final reaction product. The reaction is found to obey first‐order dependence each in [Ru(CN)5H2O3−] and [Ln]. The substituted products, viz. [Ru(CN)5L]n−3, in each case have strong MLCT transitions in visible region. The substitutional lability of [Ru(CN)5H2O]3− has been discussed in terms of electronic effect on the MOH2 bond interactions. The kinetic observation suggests that the complexation reaction of [Ru(CN)5H2O]3− with both the ligands, i.e., NRS and αNβN, follows an ion pair dissociative mechanism. The thermal activation parameters ΔH≠ and ΔS≠ have been calculated using Eyring's equation and provided in support for the proposed mechanistic scheme. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 21–30, 2011

Synthesis, structure and characterization of fac-[Re(CO) 3] + complexes derived from hydrazone Schiff bases: DFT–TDDFT investigation on electronic structures

The syntheses, structural and spectroscopic characterization of the complexes of general formula [ReL(CO) 3Cl] bearing bifunctional hydrazone Schiff base ligand L are presented in this paper. The structure of one of the complexes is determined by X-ray crystallography. The solid-state structure of the compound is involved in a secondary interaction in lattice forming a supramolecular array. The gas phase geometry optimization and electronic calculation have been performed using density functional theory without any symmetry constraints. On the basis of structural and theoretical studies, ligand in the complexes is considered to be in the keto, not in enol form. Experimental ground state IR and NMR data set agree with those calculated by DFT calculations. The electronic spectra of the complexes are calculated by time dependent density functional theory (TDDFT) using conductor like polarizable continuum model (CPCM). The computed vertical excitation energies in solution are in good agreement with experimental one showing that the metal-to-ligand charge transfer transitions in visible region dominate over ligand based ILCT transition. The TDDFT excited states calculation of the electronic spectra in solution provides evidence towards luminescence spectra.

Synthesis, spectral and electrochemical studies of alkoxo-bonded mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes incorporating tridentate ONO donor azophenolalcoholate/aldiminealcoholates

Mixed-ligand vanadyl(IV) and vanadyl(V) complexes with tridentate ONO donor azophenolalcoholate/aldiminealcoholates [viz., 2-hydroxy-2′-hydroxymethyl-5-methylazobenzene (H2L1), N-(2′-hydroxymethylphenyl)-salicylaldimine (H2L2) and N-(2′-hydroxymethylphenyl)1-hydroxy-2-naphthaldimine (H2L3)] and bidentate NN [viz., 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen)] or NO [viz., 8-hydroxyquinoline (Hhq)] donor ligands have been prepared and characterized by elemental analyses and by i.r., e.p.r. and u.v.–vis. spectroscopies. The data show that the vanadyl(IV) complexes exist in two isomeric solid forms viz., monomers and polymers, whereas vanadyl(V) complexes exist only in the monomeric form. The polymeric structure results from intermolecular V=OċċċV=O interactions. The complexes with NN donor ligands are one electron paramagnetic and display two ligand-field transitions in the visible region, whereas the complexes with ON donor ligands are diamagnetic and exhibit only LMCT bands. The vanadyl(IV) complexes display an irreversible oxidation peak near +0.30 V for complexes with (L1)2− and near +0.55 V for complexes with (L2)2− and (L3)2− ligands, while the vanadyl(V) complexes display a quasi-reversible one electron reduction couple near −0.23 V versus s.c.e. The trends in the ν(V=O), e values for the visible region transitions and the redox potential values for the vanadyl(IV) complexes have been scrutinized.

DETERMINATION OF THE ENERGY GAP OF C60 MOLECULE USING THIRD-ORDER DERIVATIVE ABSORPTION SPECTROSCOPY

More detailed absorption transitions of C60 in the visible region are observed from the third-order derivative absorption spectra.The spectra are fitted with Lorentzian line shapes,and the transition energies are determined.The assignment of the transitions in visible region is discussed,some vibronic modes are given,and finally the energy gap of C60 molecule is determined.