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-fluoresc ence characteristics in quasi-homologous N, O, S series of mono-, bi-, tri- , penta-, and quinquicyclic compounds with azocycles, whose fluorescence sp ectra cover a broad range from the ultraviolet (from lambda approximate to 260 nm) to the visible region (up to approximate to 460 nm) with quantum yi elds from gamma approximate to 0.0001 to gamma approximate to 1.0. Based on measured fluorescence parameters, including the quantum yields (gamma), li fetimes (tau), fluorescence wavelengths (lambda(max)(fl)), and half-widths of broad bands in UV absorption and fluorescence spectra (Delta lambda(fl)( 1/2)), we calculate the rate constants of radiative decay and intercombinat ion and inner conversion (k(fl), k(ST), and k(intr)), as well as absorption and stimulated-emission cross sections [sigma(13)(abs) (nu) and sigma(31)( osc) (nu)]. It is demonstrated that the replacement of carbon and oxygen at oms by sulfur always gives rise to a bathochromic shift of lambda(fl)(max); lowering of gamma, sigma(31)(osc) (nu), and k(fl); and an increase in k(ST ) in the UV and visible spectral ranges; i.e., nonoptical deactivation of e nergy of electron-vibrational excitation begins to dominate over optical de activation processes. It is shown that the periodicity of variations in opt ical properties of azocyclic compounds in the UV spectral range is consiste nt with the character of localization of electron excitation only within ac tive bond groups in the structure of molecules.