Frontier orbitals and ligand-to-metal charge transfer electronic transitions in <Emphasis Type="Italic">d</Emphasis><Superscript>0</Superscript>-metal complexes

Properties of frontier orbitals and low-energy electronic transitions in a d ⁰-organometallic complex have been studied by TDDFT and DFT methods using B3LYP hybrid functional and 3-21G*, 6-31G**, SDD, CEP-121G, and DGDZVP basis sets. It has been shown that the electronic transition between frontier orbitals in the excitation and absorption spectra is associated with charge transfer mainly from π-type ligands to a central metal d ⁰-ion. The good agreement of the data (the shape and band position of the spectra of electronic absorption and excitation, energy of electronic transitions, and strength of the harmonic oscillator) of quantum-chemical and photophysical studies is demonstrated.     

Simulation of highly emissive states based on ligand-to-metal charge transfer

Properties of the frontier orbitals of a d⁰-organometallic complex with promising photoluminescent and photosensor characteristics have been systematically studied by modern quantum-chemical methods. It has been demonstrated that the lowest electronically excited states are related to charge transfer from high-lying ligand-centered molecular orbitals to the predominantly metal-centered lowest unoccupied molecular orbital. Such an approach makes it possible to predict complexes with promising spectral-luminescent properties, including catalytic precursors of early transition metals.     

Triplet energy transfer insight in coordination of unsaturated hydrocarbons by d(0) bent metallocenes (Zr, Hf)

For a class of pi-complexes as energy donors, with the use of highly emissive d(0) metallocenes Cp(2)MCl(2) where M = Zr and Hf, it is shown that radiationless triplet energy transfer to unsaturated hydrocarbons in a rigid nonpolar methylcyclohexane (MCH) matrix (where molecular diffusion is absent) obeys the Perrin equation, occurs at radii R(0), being close to the diameter of interacting molecules, and is well described by an electron-exchange resonant (Dexter) mechanism of interaction. Principle correlation between values of the critical radius and a number of C atoms in a linear alpha-olefin is for the first time reported, viz. R(0) (Angstrom) = -2.47 + 1.35n (obtained for systems [Cp(2)HfCl(2) + CnH(2)n + MCH] at 77 K). Pronounced blue shifts (up to 1000 cm(-1)) of low-temperature emission spectra of Cp(2)ZrCl(2) in MCH in the presence of dienes, possessing nonconjugated C=C bonds, are observed, thus suggesting inner-sphere diene coordination. In view of the experimental data, inner- and outer-sphere coordinative interaction between the components of catalytic systems for polymerization (d(0) metallocene precatalysts and alkenes and dienes) is rationalized.     

Radius of energy transfer as an indicator of the interaction of aromatic amines with an olefin

Perrin-type dependences for the efficiency of quenching of phosphorescence of aromatic amines by hex-1-ene in ethanol at 77 K were obtained and the radii of nonradiative energy transfer were estimated. The critical radius of T-T energy transfer decreases with enhancement of steric hindrances in the amine molecule all other things being equal. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 250–255, February, 2008.