Krassimir K. Stavrev

On the Jahn–Teller effect on Mn2+ in zinc‐blende ZnS crystal

The excited states of Mn2+ in zinc‐blende ZnS crystal have been studied by the intermediate neglect of differential overlap model parametrized for spectroscopy within the restricted open‐shell Hatree–Fock configuration interaction approximation. The effect of the Jahn–Teller (JT) active e‐mode on the first excited state (a 4T1) has been examined with respect to energy barriers and geometric distortions. The dynamical JT effect has been studied and the excited state absorption (ESA) profiles for different e‐mode conformations have been calculated. Good reproduction of the experimental ESA spectrum has been obtained for nuclear arrangements corresponding to small S–Mn–S angle distortions. The off‐center τ2‐mode vibrations were found to promote the JT coupling by reducing the barriers between the stable structures.

A Theoretical Treatment of the Absorption and Emission Properties of Cu(II) Porphyrin

Abstract We examine the electronic spectrum of Cu(II) porphyrin using the intermediate neglect of differential overlap model. The isolated molecule is predicted to have trip-doublet absorption, corresponding to porphyrin triplets, at 9000 and 13900 cm−1. The Q band is calculated at 15900 cm−1, in good agreement with experiment. We find that coordinating with ligands such as pyridine in the fifth position leads to a state in energy below the Q band that is mostly d(z2) → d(x2−y2) but with appreciable a2u(π) → d(x2−y2) character. We postulate that the presence of this state quenches the emission when Cu(II) porphyrins are complexed with strong base ligands.

Theoretical study of the Jahn-Teller effect on the spectroscopy of VCl4

Abstract The Jahn-Teller (JT) effect in VCl 4 is studied using the intermediate neglect of differential overlap model parametrized for Spectroscopy, INDO/S. We demonstrate that the d-d bands observed in the gas phase absorption spectrum are mostly due to dynamic JT effects taking place in the ground and the first excited state of the molecule. Static distortions, favoring the ground state D 2d structures, must also be taken into account in order to correctly reproduce the shape of the absorption spectrum.

A Theoretical Study of the [Fe2(μ – S2)(P(o – C6H4S)3)2]2– Electronic Spectrum

ABSTRACT The absorption spectrum of the [Fe 2 ( μ- S 2 )(P( o- C 6 H 4 S) 3 ) 2 ] 2– complex was examined within the Intermediate Neglect of Differential Overlap model parametrized for spectroscopy using a methodology developed earlier for 2-Fe ferredoxins. We demonstrate here that the low energy UV-visible absorption spectrum of this complex can be interpreted as originating from sulfur-to-iron charge-transfer transitions. The results obtained favor the model of antiferromagnetically coupled d 5 – d 5 Fe atoms over other possibilities, for example the formation of a diamagnetic [Fe(d 6 )- S 2 0 -Fe(d 6 )] complex.

Using theoretical descriptors to model solvent effects in the isomerization of cis‐stilbene

Experimental observations of the photoinduced excited-state lifetime of cis-stilbene have shown a distinct dependence on solvation processes. The rate of decay, dominated by a cis-trans isomerization, is more rapid in polar solvents than in nonpolar solvents. Linear solvation energy relationship (LSER) techniques show that this can be explained in terms of polarity and polarizability parameters for the solvent. Theoretical linear solvation energy relationship (TLSER) analysis shows that this can be explained in terms of solvent polarizability and electrostatic basicity. New TLSER descriptors based on calculated solvent bond diplole parameters are also successful in describing this solvent dependence. Solvent-dependent dipole moments are calculated for an approximate stilbene transition-state geometry using the polarizable continuum model (PCM), which suggests the usefulness of a more detailed study of this photoisomerization process using current solvation theory and computational techniques.