V. A. Minaeva

Theoretical study of the cyclometalated iridium(III) complexes used as chromophores for organic light-emitting diodes.

Time-dependent density functional theory with linear and quadratic response technology is used to calculate electronic structure, spectra, and spin-orbit coupling effects for analysis of the main mechanism for phosphorescence of the recently synthesized iridium complex [bis(2-phenylpyridine)(2-carboxy-4-dimethylaminopyridine)iridium(III)]. This compound exhibits strong green phosphorescence which is used in solution processable organic light-emitting diode devices (OLEDs) to overcome the efficiency limit imposed by the formation of triplet excitons. Attempting to foresee new structure-property relations that can guide an improved design of OLED devices based on phosphorescence of the lowest triplet state, we have conducted a theoretical analysis of the photophysical properties of a series of iridium cyclometalated complexes.

Design of nanoscaled materials based on tetraoxa[8]circulene

Nanotubes and two-dimensional sheet-like compounds containing tetraoxa[8]circulene core units are theoretically predicted. The large cavities with a diameter of 6 Å in the 2D sheets could be useful for hydrogen storage. The designed compounds are predicted to adsorb strongly in the visible region and to be a promising material for nanophotonics because of their electron-donor properties (p-type semiconductors).

The art of the possible: computational design of the 1D and 2D materials based on the tetraoxa[8]circulene monomer

Novel one- and two-dimensional π-conjugated materials containing a tetraoxa[8]circulene monomer are designed on the basis of density functional theory techniques, including the periodic boundary condition for the infinite structures. These new materials are predicted to be the perspective ambipolar organic semiconductors showing a high mobility for hole and electron charge carriers. Furthermore, we demonstrate that the extension of π-conjugated tetraoxa[8]circulene units in the second dimension leads to a material with the HOMO–LUMO gap being significantly smaller than that for the 1D polymer ribbon. This fact clearly indicates the fundamental difference between the designed 1D and 2D semiconducting polymers, which constitutes the essence of modern “band-gap engineering”. The consistent growth of π-conjugation determines the strong visible light absorption of the studied systems in a great contrast to the initial lack of color of the tetraoxa[8]circulene compound. The possible chemical routes to synthesize the predicted materials are discussed, including free Gibbs energy estimation for the proposed reactions.

Single crystal architecture and absorption spectra of octathio[8]circulene and sym-tetraselenatetrathio[8]circulene: QTAIM and TD-DFT approach

AbstractThe single crystal architecture of the high-symmetry octathio[8]circulene and sym-tetraselenatetrathio[8]circulene is studied at the density functional theory (DFT) level with the quantum theory of atoms in molecules (QTAIMs) approach to the electron density distribution analysis. The presence of stabilizing intermolecular C---C, C---S and C---Se contacts in the longitudinal and transversal projections of the single crystals is postulated on the grounds of the previous high-resolution X-ray data for octathio[8]circulene; it is supported by the present QTAIM calculations and also predicted in some new details for both circulenes. We suggest that the appearance of the observed red color for the monocrystalline octathio[8]circulene is caused by strong intermolecular interactions between the molecules in the single crystal. However, the intermolecular interactions for the sym-tetraselenatetrathio[8]circulene crystal fragment are weaker and molecular layers are more friable in comparison to octathio[8]circulene crystal structure. These lead to the absence of visible absorption for the sym-tetraselenatetrathio[8]circulene crystal. Graphical abstract3D architecture of molecular crystals for two studied circulenes

A comparative study of the electronic structure and spectra of tetraoxa[8]circulene and octathio[8]circulene

The electronic structure and spectra of two highly symmetric molecules of circulenes, namely, tetraoxa[8]circulene and octathio[8]circulene, which belong to the symmetry point groups D4h and D8h, respectively, have been investigated by the density functional theory (DFT) method using the hybrid functional B3LYP in the 6–31G(d) basis set. The infrared (IR) spectra of these molecules in the ground and excited triplet states have been compared. The comparison of the electronic absorption spectra of both molecules has revealed that the first electronic transition is forbidden and determined by the electronic-vibrational interaction due to the degenerate eu modes. The ability of the studied circulenes to fluoresce and phosphoresce has been analyzed, because these compounds are of interest as promising materials for organic light-emitting diodes.

Structure and Spectral Properties of Truxene Dye S5

On the ground of functional theory with the B3LYP and BMK functionals, we have studied the structure and optical properties of a truxene dye sensitizer S5 for photoelectric transducers. Based on the calculations of the vertical excitations energy of the dye molecule and accounting the influence of the solvent, we have revealed a positive solvatochromic effect that is weak compared to results obtained in the vacuum approximation. We have studied new features describing stabilization of the planar structure of the cyanothiophene-acrylic fragment of the S5 dye.

Quantum-chemical study of the structure and optical properties of sensitized dyes of an indoline-thiazolidine series

Based on the density functional theory, quantum-chemical calculations of the structure and electronic absorption spectra of the molecules D102, D149, and D205 of an indoline-thiazolidine series, which are used as sensitizers for solar cells, are performed. Circular dichroism spectra are predicted. The mechanisms by which intra- and intermolecular electron transfer occur upon excitation to a triplet state, as well as the relaxation mechanism, are described. The geometric and electronic structures of the molecules under study in the ground singlet and excited triplet states are considered, and the relation between their structure and photochemical properties is discussed.

Fluorescence and FTIR Spectra Analysis of Trans-A2B2- Substituted Di- and Tetra-Phenyl Porphyrins

A series of asymmetrically substituted free-base di- and tetra-phenylporphyrins and the associated Zn-phenylporphyrins were synthesized and studied by X-ray diffraction, NMR, infrared, electronic absorption spectra, as well as fluorescence emission spectroscopy, along with theoretical simulations of the electronic and vibration structures. The synthesis selectively afforded trans-A2B2 porphyrins, without scrambling observed, where the AA and BB were taken as donor- and acceptor-substituted phenyl groups. The combined results point to similar properties to symmetrically substituted porphyrins reported in the literature. The differences in FTIR and fluorescence were analyzed by means of detailed density functional theory (DFT) calculations. The X-ray diffraction analysis for single crystals of zinc-containing porphyrins revealed small deviations from planarity for the porphyrin core in perfect agreement with the DFT optimized structures. All calculated vibrational modes (2162 modes for all six compounds studied) were found and fully characterized and assigned to the observed FTIR spectra. The most intense IR bands are discussed in connection with the generic similarity and differences of calculated normal modes. Absorption spectra of all compounds in the UV and visible regions show the typical ethio type feature of meso-tetraarylporphyrins with a very intense Soret band and weak Q bands of decreasing intensity. In diphenyl derivatives, the presence of only two phenyl rings causes a pronounced hypsochromic shift of all bands in the absorption spectra. Time-dependent DFT calculations revealed some peculiarities in the electronic excited states structure and connected them with vibronic bands in the absorption and fluorescence spectra from associated vibrational sublevels.

MCSCF response calculations of the excited states properties of theO2 molecule and a part of its spectrum

A number of transitions including the triplet–singlet band f′1Σu+←X3Σg−, have been studied by ab initio multi-configurational self-consistent field (MCSCF) response methods. Potential energy curves for eight excited states obtained by linear response calculation are in a good agreement with recent experimental data and exhibit some new findings. Quadrupole moments for the 12 lowest states have been calculated which can be used for intermolecular interaction analysis and solvent shift estimations. The nuclear quadrupole coupling constant, magnetizability tensor, nuclear spin–rotation coupling constant and rotational g-factor are also presented. For the three lowest singlet states these parameters are analyzed in detail.

A DFT and QTAIM study of the novel d-block metal complexes with tetraoxa[8]circulene-based ligands

A series of transition metal (d-block metals) ion complexes with the tetraoxa[8]circulene-based ligand having one- and two-decker (sandwich-type) structures has been designed and studied in the framework of the DFT approach. The quantum theory of atoms in molecules (QTAIM) was additionally applied for the studied complexes with the aim of evaluating their peculiar electronic features. The obtained results indicate that the complexation process depends on matching of the transition metal cation size to the size of the tetraoxa[8]circulene-formed cavity similar to the formation of the crown ether complexes. Coordination bonds of the d-block metal ions with the neighbouring oxygen atoms in the studied complexes can be interpreted as an intermediate type of interaction. The binding energy of the coordinative M–O bonds has been calculated both by the Espinosa equation and the DFT additive scheme in order to confirm the high stability of the studied systems. If the size of metal cations is larger than the corresponding crown cavity the formation of two-decker complexes with the two tetraoxa[8]circulene-based ligands is possible. Such sandwich-type complexes possess the unusual cubic coordination polyhedron of the central metal ion bound to eight oxygen atoms. Moreover, these complexes are additionally stabilized due to the presence of π-stacking interactions between the two opposite tetraoxa[8]circulene parallel sheets. The synthesis of the proposed π-extended tetraoxa[8]circulene sheets and their metal-complexation ability attract special attention because of their promising application as potential biomimetic-type nanopores.