Victor N. Cherepanov

Computational studies of photophysical properties of porphin, tetraphenylporphyrin and tetrabenzoporphyrin.

The molecular photonics of porphyrins are studied using a combination of first-principle and semi-empirical calculations. The applicability of the approach is demonstrated by calculations on free-base porphyrin, tetraphenylporphyrin, and tetrabenzoporphyrin. The method uses excitation energies and oscillator strengths calculated at the linear-response time-dependent density functional theory (TDDFT) or the corresponding values calculated at the linear-response approximate second-order coupled-cluster (CC2) levels. The lowest singlet excitation energies obtained in the TDDFT and CC2 calculations are 0.0-0.28 eV and 0.18-0.47 eV larger than the experimental values, respectively. The excitation energies for the first triplet state calculated at the TDDFT level are in excellent agreement with experiment, whereas the corresponding CC2 values have larger deviations from experiment of 0.420.66 eV. The matrix elements of the spin-orbit and non-adiabatic coupling operators have been calculated at the semi-empirical intermediate neglect of differential overlap (INDO) level using a spectroscopic parameterization. The calculations yield rate constants for internal conversion and intersystem crossing processes as well as quantum yields for fluorescence and phosphorescence. The main mechanism for the quenching of fluorescence in tetraphenylporphyrin and tetrabenzoporphyrin is the internal conversion, whereas for free-base porphyrin both the internal conversion and the intersystem crossing processes reduce the fluorescence intensity. The phosphorescence is quenched by a fast internal conversion from the triplet to the ground state.

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.

Theoretical investigation of the ethylene dimer: Interaction energy and dipole moment

The interaction potential energy and the interaction‐induced dipole moment surfaces of the van der Waals C2H4‐C2H4 complex has been calculated for a broad range of intermolecular separations and configurations in the approximation of rigid interacting molecules. The calculations have been carried out using high‐level ab initio theory with the aug‐cc‐pVTZ basis set and within the framework of the analytical description of long‐range interactions between ethylene molecules. Binding energy for the most stable configuration of the C2H4‐C2H4 complex was calculated at the CCSD(T)/CBS level of theory. The harmonic fundamental vibrational frequencies for this complex were calculated at the MP2 level of theory.

Dipole moment surface of the van der Waals complex CH4–N2

The interaction-induced dipole moment surface of the van der Waals CH(4)-N(2) complex has been calculated for a broad range of intermolecular separations R and configurations in the approximation of the rigid interacting molecules at the MP2 and CCSD(T) levels of theory using the correlation-consistent aug-cc-pVTZ basis set with the basis set superposition error correction. The simple model to account for the exchange effects in the range of small overlap of the electron shells of interacting molecules and the induction and dispersion interactions for large R has been suggested. This model allows describing the dipole moment of van der Waals complexes in analytical form both for large R, where induction and dispersion have the key role, and for smaller R including whole ranges of their potential wells, where the exchange effects are important. The proposed model was tested on a number of configurations of the CH(4)-N(2) complex and was applied for the analytical description of the dipole moment surface for the family of the most stable configurations of the CH(4)-N(2) complex.

Theoretical investigation of the potential energy surface of the van der Waals complex CH4–N2

The interaction potential energy surface of the van der Waals CH(4)-N(2) complex has been calculated for a broad range of intermolecular separations and configurations in the approximation of rigid interacting molecules at the CCSD(T) and MP2 levels of theory using the correlation consistent aug-cc-pVTZ basis set. The BSSE correction was taken into account for all the calculations. The most stable configurations of the complex were found. Binding energies were calculated in the CBS limit with accounting for the molecular deformations. The harmonic and anharmonic fundamental vibrational frequencies and rotational constants for the ground and first excited vibrational states were calculated for the most stable configurations at the MP2 level of theory with BSSE correction. Fitting parameters were found for the most stable configuration for the Lennard-Jones and Esposti-Werner potentials.

Electronic absorption spectrum of monoamine tetraphenylporphyrin with the complexon of ethylenediaminetetraacetic acid as substitute

In the framework of density functional theory the equilibrium geometry of the ground electronic state of monoamine tetraphenylporphyrin with the complexon of ethylenediaminetetraacetic acid was found using B3LYP functional and 6-31G(d,p) basis set. Electronic absorption spectrum of this molecule in ethanol solution was measured in the range of 300-600nm and interpreted using the PCM/TDDFT method (with the B3LYP, CAMB3LYP, M06-2X functionals) with 6-31G(d,p) and 6-31++G(d,p) basis sets. The observed and calculated line positions and intensities are well agreed.

Static polarizability surfaces of the van der Waals complex CH4–N2

The static polarizability surfaces of the van der Waals complex CH(4)-N(2) have been calculated for a broad range of intermolecular separations and configurations in the approximation of rigid interacting molecules. The calculations have been carried out at the CCSD(T) and MP2 levels of the theory using the aug-cc-pVTZ basis set with the BSSE correction and within the framework of the classical long-range multipolar induction and dispersion interactions. It was shown that the results of analytical polarizability calculations for the CH(4)-N(2) complex are in a good agreement with the ab initio polarizabilities in the outer part of the van der Waals well on the complex potential surface. Ab initio calculations of the polarizability tensor invariants for the complex being in the most stable configurations were carried out. The change in the polarizability of CH(4)-N(2) due to the deformation of the CH(4) and N(2) monomers at the formation of the complex was estimated. In the framework of the analytical approach the polarizability functions alpha(ii)(R) of the free oriented interacting molecules CH(4) and N(2) were calculated.

Multipole Electric Moments and Higher Polarizabilities of Molecules: Methodology and Some Results of ab initio Calculations

The technique of calculation of electric multipole moments and higher molecular polarizabilities is described. With the help of high-level ab initio methods (R)CCSD(T) and CCSD(T) with different aug-ccVXZ basis sets (X = Q, 5) dipole, quadrupole, octupole, hexadecapole moments and dipole, dipole-quadrupole, dipole-octupole, quadrupole-quadrupole polarizabilities of H2, O2, N2, CO2, CO, CN, HCl, HCN, NaCl, OH, N2H+, CH4, and H2O molecules have been calculated.

On some aspects of changing the sign of the dipole moment functions of diatomic molecules

Ab initio calculations of asymptotic dipole moment functions of some diatomic molecules at R → 0 have been carried out. It was achieved that in a range of small internuclear separations, the dipole moment functions of the molecules CO, NO, BF and BeNe for ground electronic states have an additional change of the sign.

Static hyperpolarizability of the van der Waals complex CH4N2

The static first hyperpolarizability of the van der Waals CH4N2 complex was calculated. The calculations were carried out in the approximation of the rigid interacting molecules for a broad range of intermolecular separations (R = 6–40 a0) and for six configurations at CCSD(T) level of theory using the correlation consistent aug‐cc‐pVTZ basis set with the basis set superposition error correction. It was shown that the long‐range classical approximation, including the terms up to R−6, is in a good agreement with ab initio calculations for R > 11 a0. It was found out that for the family of most stable configurations of the complex, the first hyperpolarizability invariants practically do not change (the changes are less than 0.1%). Under forming the stable van der Waals CH4N2 complex, the intensity and degree of depolarization of the hyper‐Rayleigh scattering are noticeable decreased (by ∼10%) to be compared with the free CH4 and N2 molecules.