Regularities of variations in spectral-fluorescence properties and the nature of intramolecular interaction in N, O, S series of heterocyclic azoles in the UV range of optical spectrum

This paper investigates the regularities of variations in spectral-fluorescence characteristics in quasi-homologous N, O, S series of mono-, bi-, tri-, penta-, and quinquicyclic compounds with azocycles, whose fluorescence spectra cover a broad range from the ultraviolet (from λ ≈ 260 nm) to the visible region (up to ≈460 nm) with quantum yields from γ ≈ 0.0001 to γ ≈ 1.0. Based on measured fluorescence parameters, including the quantum yields (γ), lifetimes (τ), fluorescence wavelengths (λflmax), and half-widths of broad bands in UV absorption and fluorescence spectra (γλfl1/2), we calculate the rate constants of radiative decay and intercombination and inner conversion (kfl, kST, and kintr), as well as absorption and stimulated-emission cross sections [σ13abs (ν) and σ31osc (ν)]. It is demonstrated that the replacement of carbon and oxygen atoms by sulfur always gives rise to a bathochromic shift of λflmax; lowering of γ, γ31osc (ν), and kfl; and an increase in kST in the UV and visible spectral ranges; i.e., nonoptical deactivation of energy of electron-vibrational excitation begins to dominate over optical deactivation processes. It is shown that the periodicity of variations in optical properties of azocyclic compounds in the UV spectral range is consistent with the character of localization of electron excitation only within active bond groups in the structure of molecules. Copyright © 1999 by MANK "Hayκa/Interperiodica".