The physical principles of simulating the structure and photophysical properties of complex heteroaromatic compounds by means of the LCAO MO SCF methods

Physical principles of the simulation of structure, spectral-luminescence, and lasing properties of complex N, O, and S heteroaromatic molecules by means of the quantum-chemical LCAO MO SCF PPP (Parisier-Parr-Pople approximation) methods within the framework of the CNDO/S and INDO/S (complete and intermediate neglect of differential overlap, sp-valence basis) approaches are considered. The principles of applying quantum mechanics to the computation of spectral parameters of laser molecular systems, such as fluorescence and phosphorescence quantum yields and lifetimes (γfl, τfl, γPh, and τPh), stimulated emission cross sections (σ31osc), cross sections of reabsorption through the T1 → Tn (σ2T*) and S1* → Sn* (σ3s*) transitions at pumping and lasing wavelengths, and the ultimate duration of the pumping pulse when lasing is still possible in a laser active clement, are discussed. The principles of control of the molecular structure; the properties of the excited singlet (Si*) and triplet (Ti) states; and the parameters of the S0 → Sn*, S1* → Sn*, T1 → Tn, and T1 → S0 transitions aimed at the selection of organic luminophores with preset properties for specific scientific and technical applications are demonstrated. Specific examples are considered, and new UV laser-active molecules with improved optical parameters (compared with the catalogued molecules) are reported. Copyright © 1997 by MAIIK Hayka/Interperiodica Publishing.