The computational and experimental investigations of photophysical and spectroscopic properties of BF2 dipyrromethene complexes.

The electronic excited states of BF2 dipyrromethene (2BrDPM, DPMI, DPMII, PM567 and 4PhDPM) complexes were investigated using the extended multi-configuration quasi-degenerate at the second order of perturbation theory (XMCQDPT2) and the second-order approximate coupled-cluster (CC2) methods. The excitation energies calculated by CC2 are significantly overestimated by 0.42-0.59 eV because of the substantial contributions of double excitation levels to excited states (>10%). However, the calculated XMCQDPT2 excitation energies agree well with experimental ones within the accuracy 0.11-0.20eV. The very low lasing efficiency (7.8-8.4%) of 4PhDPM compound was explained by the T1→T4 and T1→T5 reabsorptions at XMCQDPT2 level of theory. The molecular photonics of pyrromethenes are studied using a combination of the first-principle and semi-empirical calculations. The main mechanism for the deactivation of the energy of the first singlet excited electronic state is the radiative electronic transition for DPMI, DPMII, PM567 and 4PhDPM compounds. Also, the main mechanism for the quenching of fluorescence in considered complexes (except DPMII compound) is the internal conversion. The processes of the internal conversion and intersystem crossing compete with each other in DPMII compound. The measured and calculated fluorescence quantum yields agree well for all considered molecules.

[Peculiarities of electrostatic interactions between amino acids and salicylic acid in aqueous solution].

Based on calorimetric data, the enthalpy of the transfer of salicylic acid to aqueous buffer solutions with the addition of different amino acids at the constant acidity of medium pH 7.35 was determined. It was shown that the exothermicity of transfer and negative enthalpic coefficients for these pairwise interactions of salicylic acid with amino acids considerably increase with increasing charge of amino acid existing in the ionic form under these conditions. Weak interactions of salicylic acid with the anionic form of aspartic and glutamic acids are related to the repulsion between anion carboxyl groups. More intensive interactions are observed for zwitter-ions of glycine and alanine. The most intensive specific interactions with salicylic acid are observed for lysine and arginine, which exist in the solution as cations.