Reactivity patterns of imidazole, oxazole, and thiazole as reflected by the polarization justified Fukui functions.

The concept of the polarization justified Fukui functions has been tested for the set of model molecules: imidazole, oxazole, and thiazole. Calculations of the Fukui functions have been based on the molecular polarizability analysis, which makes them a potentially more sensitive analytical tool as compared to the classical density functional theory proposals, typically built on electron density only. Three selected molecules show distinct differences in their reactivity patterns, despite very close geometry and electronic structure. The maps of the polarization justified Fukui functions on the molecular plane correctly identify important features of the molecules: the site for the preferential electrophilic attack in imidazole (-NH, see the TOC image) and oxazole (5-C), as well as uniquely aromatic character of the thiazole molecule and the acidic forms XH(+) of all three species.

Single- and two-photon excited fluorescence in organic nonlinear optical single crystal 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole.

Fluorescence of nonlinear optical organic single crystal of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) excited by a nonabsorbed light pulses from Q-switched Nd:YAG laser λ = 1064 nm as well as absorbed λ = 532 nm light is reported. Two mechanisms of two-photon excited fluorescence are considered: (i) direct two-photon excited fluorescence and (ii) single-photon excitation due to reabsorption of light generated in process of second harmonic generation (SHG) by the crystal due to its nonlinear optical properties. Strong anisotropy of fluorescence that has been observed is linked with uniaxial molecular alignment. Fluorescence decay profile shows two- exponential decay with lifetimes of emitting species of 3.7 and 5.6 ns at 293 K. The excitation and fluorescence spectra of the DCNP single crystal have been measured at 294 K and in function of temperature down to 77.4 K. The strong bathochromic shift of fluorescence spectrum in crystal with respect to fluorescence of DCNP molecule in solution is observed and interpreted with possible formation of molecular aggregates.

Polarization justified Fukui functions: the theory and applications for molecules.

The Fukui functions based on the computable local polarizability vector have been presented for a group of simple molecules. The necessary approximation for the density functional theory softness kernel has been supported by a theoretical analysis unifying and generalizing early concepts produced by the several authors. The exact relation between local polarizability vector and the derivative of the nonlocal part of the electronic potential over the electric field has been demonstrated. The resulting Fukui functions are unique and represent a reasonable refinement when compared to the classical ones that are calculated as the finite difference of the density in molecular ions. The new Fukui functions are strongly validated by their direct link to electron dipole polarizabilities that are reported experimentally and by other computational methods.

Polarization justified Fukui functions.

New Fukui functions have been derived within the conceptual density functional theory by the analysis of the polarization effect of a system in static electric field. Resulting Fukui functions accurately reproduce the global softness and electronic dipolar polarizability; they meet the condition integral[f(r)/r]dr = -(partial differential mu/partial differential Z)(N) and lead to very reasonable values of the global hardness for atoms for the group of 29 main group elements. Computational clarity makes the new Fukui functions a promising tool in studies of molecular reactivity.

Usefulness of spectroscopy for biomedical engineering.

Modifications of phenylalanine amino acid after its exposure to near-infrared (NIR) radiation have been investigated using ATRFTIR (Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy). The process of amino acid aggregation after its exposure to NIR has been observed. A possible mechanism of amino acid dimer formation has been proposed with the help of theoretical calculations of quantum mechanics (MP2 and B3LYP/6-31 G* level) using the GAUSSIAN 03 package. The usefulness of spectroscopy for biomedical engineering is discussed. ATR-FTIR appears to be a powerful tool for measuring tissue damage in aqueous environments.

Low-temperature photoluminescence of p-nitroaniline and o-methyl-p-nitroaniline crystals.

Photoemission spectra of para-nitroaniline (p-NA) and ortho-methyl-para-nitroaniline (MNA) single crystals measured between 5 and 250K revealed that the MNA crystals emit phosphorescence and fluorescence in contrast with the p-NA crystals which have only fluorescence. It is assumed that the fluorescence of p-NA crystals at 5K originates from the doublet state of negatively charged polarons while the fluorescence of MNA crystals at 60K is due to trap states. The Stokes shift between absorption and emission onsets, measured at 5K, is much larger in the p-NA crystals than in the MNA and meta-nitroaniline (m-NA) crystals. This fact is rationalized by different geometrical changes caused by excitation.