Tomasz Misiaszek

Solvent effect on static vibrational and electronic contribution of first-order hyperpolarizability of π-conjugated push–pull molecules: quantum-chemical calculations

Abstract Results of ab initio quantum-chemical calculations of the first-order static electronic (βe) and vibrational (βv) hyperpolarizabilities for the prototype push–pull conjugated molecules 4-nitro-aniline, 4-nitro-4′-aminostilbene, 4-amino-4′-nitrobiphenyl, and 4-amino-4′-nitrodiphenylacetylene in the gas phase and in chloroform and aqueous solvents are presented. The coupled perturbed Hartree–Fock method and the sum-over-modes formalism was used to calculate individual components of βe and βv tensors. The solvent effect has been included via the continuum self-consistent reaction field model. The calculations demonstrate the existence of larger solvent effect on the βv compared with βe for molecules investigated in this paper.

Dynamical disorder in 2-methyl-4-nitroaniline and its deuterated analogue crystals studied by Fourier transform infrared and nuclear magnetic resonance.

The Fourier transform infrared spectra of the thin layers of 2-methyl-4-nitroaniline (MNA) and its deuterated analog were recorded in the 500-4000 cm(-1) region in the 10-300 K temperature range. Activation energies of the -CH(3), -NH(2), and -NO(2) groups reorientations were estimated. The (1)H-NMR spin-lattice relaxation time, T(1), and the second moment of (1)H-NMR resonance line, M(2), measured in the 80-298 K temperature range, were used to determine the parameters of the -CH(3) group motion. The experimental potential barriers for the amine, nitro, and methyl group reorientations are considered in the context of strengths of the N-H([ellipsis (horizontal)])O, C-H([ellipsis (horizontal)])O intermolecular hydrogen bonds, and other short contacts, recognized recently [U. Okwieka et al., J. Raman Spectrosc. 39, 849 (2008)], and they agree with the barriers calculated by quantum chemical methods. The dynamical disorder found in the MNA crystal in the large temperature range seems to be important from the point of view of its nonlinear optical and other properties.

Thermally induced rearrangement of hydrogen-bonded helices in solid 4-isopropylphenol as studied by calorimetric, proton NMR, dielectric and near IR spectroscopic methods

Abstract Calorimetric, dielectric and Fourier transform near infrared (IR) spectroscopic methods were used to study molecular dynamics and structural transition in solid 4-isopropylphenol (4IP) above room temperature. Pulse proton nuclear magnetic resonance (NMR) measurements were performed in the 100–340 K temperature range. A phase transition was found at 331.5 K, 1.5 K below the melting point. Energetically inequivalent methyl groups reorientations were observed in differently prepared samples and this suggested that a high-temperature polymorph occurs below the transition point as a metastable phase. Dielectric relaxation measurements showed an electric conductivity similar in value to that in water. This was detected as a pronounced contribution to the imaginary part of dielectric permittivity at temperatures higher than 310 K. Near IR spectra revealed that hydrogen bondings are stronger in the high-temperature phase than in the room-temperature-stable one. We propose that thermally induced molecular rearrangements enable proton transfer in hydrogen bonds (HBs) and this stimulates protonic conduction.

Solvent effect on the vibrational spectrum of Michler's ketone. Experimental and theoretical investigations.

We examined solvent effect on the IR and Raman spectra of MK in several solvents of different polarity and proticity, for understanding of intermolecular interactions, focusing on solvent effect in detail. It has been found that change of solvent polarity has an ambiguous influence on solvatochromism of MK. We have observed that not only vibrations of carbonyl group are affected by the solvent polarity, but also mode ν(CN) and ν(CC) in IR and Raman spectra of MK. Experimental investigations have been supported by the quantum-mechanical computations to gain more insight into the solvatochromic behavior of Michlers ketone. Calculations have been carried using Kohn-Sham formulation of Density Functional Theory (DFT) and the Polarizable Continuum Model (PCM) was employed to account for solute solvent interactions.

Atomic charge distribution in 4-isopropylphenol molecule derived from atomic polar tensors

Abstract On the basis of the calculated atomic polar tensors the generalized atomic polar tensor charges have been calculated for 4-isopropylphenol (4-IP) and related compounds: benzene, quinone, phenol and p -nitroaniline ( p -NA). The second order Moller–Plesset perturbation method and Huzinaga–Dunnings double valence ζ basis set supplemented by d polarisation function on heavy atoms and p on hydrogen atoms (D95V ∗∗ ) have been used. Analysis of the atomic charges has been done. It is found that the phenyl rings of the 4-IP and p -NA molecules have an intermediate structure between the aromatic ring and the quinoid one.

The nature of interactions in nicotinamide crystal

In this study, we analyze the nature of intermolecular interactions in nicotinamide complexes appearing in conformations found in the crystal structure, including many-body effects. In doing so, we employ symmetry-adapted perturbation theory based on density functional theory description of monomers, and we perform the many-body variational-perturbational interaction energy decomposition. The principal finding of this study is that the stability of nicotinamide complexes is a complicated interplay of four (large in magnitude) interaction-energy components, i.e. induction, dispersion, electrostatic and exchange repulsion. However, the last two contributions cancel each other out to a large extent. In the case of considered three-body complexes, the nonadditivity effects are found to be not important. Based on the results of topological analysis of charge densities we characterized also the properties of short H ⋯ H contact and identified it as a weak noncovalent closed shell interaction.