Physical properties of nanosystems with π-conjugated intermolecular bonds
Authors:   Taras Shevchenko National University of Kyiv, Kyiv, Pavlenko O.L. , Dmytrenko O.P. ,   Taras Shevchenko National University of Kyiv, Kyiv, Kulish M.P. ,   Taras Shevchenko National University of Kyiv, Kyiv, Lizunov V.V. ,   G. V. Kurdyumov Institute for Metal Physics, of the NAS of Ukraine, Kyiv, Kachkovsky О. D. ,   Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine, Kyiv
Published: November 2024

Systematical study of the structure and properties of π-conjugated molecules with different topology both in the independent state and in the complexes is presented. For linear π-conjugated molecules, on the example of neutral polymethine squarain, merocyanine dyes and their bases, it is shown that the spectra of these molecules are sensitive to the type and location of heteroatoms, donor-acceptor functional groups in the π-branched electronic system. Quantum-mechanical analysis of charge distribution in one-dimensional π-electron systems at injection of 1-5 charge carriers, both for the elongated linear and broadened polymethine chains, was performed and the formation of soliton-like waves was shown. In the condensed state, when the dyes form the films, the shift and broadening of the absorption maxima are observed, compared to the spectra in the solutions. That is caused by the aggregation of molecules, which depends on the charge distribution in their chromophores. The interaction of the dyes with fullerenes both in the films and solutions leads to the electronic structure rearrangement, which manifests itself in new spectral effects. Quantum mechanical analysis points on the charge transfer from dye molecules to the carbon nanostructures. That fact and also splitting of the degenerate levels of C 60 induces significant changes of the energy gap of the complexes. The main contribution to the absorption intensity is caused by HOMO (delocalized on dye chromophore) – LUMO (localized on fullerene) transition. In the complexes of squaraine dye with carbon nanoparticles (fullerenes, graphene, nanotube) the charge transfer from the dye to the carbon nanoparticles is observed. The latter leads to redistribution of charges along the surface of the nanoparticles, change in their geometry, including lowering of symmetry of the fullerene, the appearance of a dipole moment and redistribution of electronic levels. Changes in the energy gap of complexes are due to differences in the electronic structure of carbon nanoparticles. In the case of a covalent bonding between linear dye molecules and C60 fullerenes, the redistribution of the molecular orbitals of the complexes differs from similar complexes with stacking interaction. Ability of fullerene to form stable p®p- complexes with biologically active compounds, that are the derivatives of 1,3-oxazole containing donor -acceptor substituents, is considered basing on the spectral and quantum-chemical analysis. For the solutions of antitumor agents doxorubicin, gemcitabine, containing π-conjugated fragments, complexation with albumin is observed. It is shown that the complexation is based on the p®p-stacking of aromatic aminoacids of BSA and aromatic cycles of the drugs. It is shown that the binding constants decrease under conjugation of the molecules with gold nanoparticles. The described results are important in the bionanotechnology and nanoelectronics.