Excited electronic states of complex heteroatomic molecules in series and in different aggregation states of matter

Abstract

We investigate the spectroscopic and photophysical properties of new series complex molecules, which is capable of fluorescence and some generating light in solvents of various kinds within the wavelength region 308 - 420 nm with a high fluorescence quantum yield (gamma) equals 0.01 - 0.97 and a low threshold pump density E<SUB>lp</SUB>(P<SUB>lp</SUB>). We worked from the measured lifetimes and to calculate the rate constants for radiative decay (K<SUB>fl</SUB>) and intercombinational conversion, (K<SUB>ST</SUB>), the cross section for a stimulated emission ((sigma) <SUB>31</SUB><SUP>osc</SUP>), and the characteristic time t<SUB>lp</SUB> in solvents of various types and in the vapor. The latter is the limiting rise time of the pump pulse (t<SUB>lp</SUB>) at which the generation of electromagnetic radiation is still possible. The cross sections for the induced singlet-singlet ((sigma) <SUB>3S</SUB><SUP>*</SUP>) and triplet-triplet ((sigma) <SUB>2T</SUB><SUP>*</SUP>) absorption in the generation band, required for calculating t<SUB>lp</SUB>, were taken from a variety of sources: experimental and for all other complex molecules, we used results calculated by some semiempirical methods SCF MO LKAO the Pariser-Parr-Pople (PPP/CI) and in complete neglect of differential overlap (INDO/S-CI). The results show that the decrease or increase of in the switch from solution to vapor, or as the properties of the solvent change, stems from dynamic separation or overlap of the lasing and induced absorption bands of the S<SUB>1</SUB><SUP>*</SUP> yields S<SUB>n</SUB><SUP>*</SUP> and T<SUB>1</SUB> yields T<SUB>n</SUB> transitions. Lasing does not occur in concentrated acids because of the nearly complete overlap of the limiting gain and induced absorption T<SUB>1</SUB> yields T<SUB>n</SUB> transitions (compare it with the behavior of dyes in their chemo absorbed state). Using the density matrix method, we show that the solvent affects the distribution of electron density among the individual atoms and fragments of the complex geteratomic molecule in the ground state, leading to systematic changes in geometry. As a result, there are changes in the distribution of bond lengths in the rings of the azo-cycles aromatic molecule. Photonation of the nitrogen atoms in the azocycles molecules changes the structure of the excited electronic singlet (S<SUB>i</SUB><SUP>*</SUP>) and (T<SUB>i</SUB>) triplet states and in the transitions S<SUB>O</SUB> yields S<SUB>n</SUB><SUP>*</SUP>, S<SUB>1</SUB><SUP>*</SUP> yields S<SUB>0</SUB>, S<SUB>1</SUB><SUP>*</SUP> yields S<SUB>n</SUB><SUP>*</SUP>, T<SUB>1</SUB> yields T<SUB>n</SUB>, T<SUB>1</SUB> yields S<SUB>0</SUB>, which determine the spectroscopic and generation characteristics of the complex compounds. The calculated geometry vapor complex molecules and [(sigma) (pi) ]-anion and [(sigma) (pi) ]-kation radicals compound AM-1/CI and PPP/CI methods in the ground state in their chemosorbtion state of the surface.