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Physical principles of the simulating of structure, spectral-luminescence, and lasing properties of complex N, O, S heteroaromatic molecules by means of the quantum-chemical one-electron approximation models LCAO-MO SCF CI CNDO/S and INDO/S (complete and intermediate neglect of differential overlap, sp-valence basis), PPP/S (Pariser-Parr-Pople σπ*-approximation) approaches are considered. The principles of control of the molecular structure; the properties of the excited singlet (Si*) and triplet (Ti) states; and the parameters of the S1*→S0,S0→Sn*,S1*→Sn*,T1→Tn and T1→S0 transitions aimed at the selection of organic luminophores and UV-laser-active molecules with preset properties for specific scientific and technical applications are demonstrated. In LCAO-MO CSF CI methods, the wave function of the quantum systems contains the information on each atom and spectral parameters of atoms. The ionization potential and the electron affinity are taken from the gas-phase experiments. A complex multiatomic molecule can be represented as a system of excited electronic states with different spin and orbital structures where the energy of a quantum evolves under the action of intramolecular mechanisms with determine photophysical and photochemical properties of organic molecules.
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