Navozenko O. Photophysical properties and development of composites based on cyanine dyes for low energy consuming light-emitting sources

The PhD thesis is devoted of studying of the physical properties of new light-emitting composite materials based on cyanine dyes. Computer simulation of the spatial structure and low-lying excited states of cyanine dyes and matrix molecules was performed. By modifying the chemical structure of styryl dyes and their neutral bases, the possibility of varying the absorption region in almost the entire visible range of radiation is realized. It is shown that the dipole moments in these compounds differ significantly in modulus and direction. It has been found that the cyclization of both terminal groups of symmetrical cyanine dye by BF2 bridge makes the total charge of molecule neutral but practically does not change the bond lengths in the π-electron system, and the neutral molecule, in turn, can be thermally deposited in vacuum. Also, the cyclization of cyanine molecules by the BF2 (BF2O) bridge gives rigidity of the molecular framework and thus leads to an increase in quantum yield. Series of new boron-containing molecules with a high quantum yield have been fabricated for thermal vacuum deposition. Based on these borcontaining molecules as impurities, composite high-performance fluorescent thin films are made by the thermal vacuum deposition. It is shown that it is possible to select such modes of film deposition in which the decomposition of the starting material does not occur. There are no spectral manifestations of destructive fragments in the studied films. For the first time the absorption and fluorescence spectra of new composite films were studied and their absorption and emission centers were identified. It was shown that at concentrations of boron-containing impurities in the Alq3 matrix of more than a few percent, the radiation intensity is significantly reduced due to the formation of aggregates. Analysis of the absorption, transmission and fluorescence spectra of composite films and computer simulation results of mutual spatial arrangement between dyes molecules indicates the presence of H-aggregates. The phenomenon of electronic excitation energy transfer in composite films is established and analytically described. The main evidence of the presence of electron excitation energy transfer is the fact that during excitation into the absorption region of the matrix molecules, the emitted depolarized radiation occurs in the fluorescence region of impurities. In this case, insignificant radiation is recorded in the spectrum region of the matrix with attenuation times less than the attenuation times in the spectrum region of impurities. The processes of electron excitation transfer in the Alq3 matrix were analytically described within the framework of the Faydish diffusion model of exciton motion. The most efficient transfer of excitation from matrix molecules to impurity molecules occurs at impurity concentrations of ~ 1-2%. The obtained lengths of the average run of singlet excitons in the films "Alq3-impurity" are 130-200 Å, the diffusion coefficient of excitons D is 3.3*10-4 cm2/s. Due to the change in the chemical structure of the investigated boron-containing dyes, such a total radiation spectrum of impurity compounds 1415, 2983, 2414, 3022 was obtained that with the Alq3 matrix it covers almost the entire visible range.