Excited states, generation of light, and photoprocesses in series of complex N, O, S polyatomic molecules

The photophysical properties of some new and also some known complex organic molecules emission and generated radiations in the wavelength interval 340 - 560 nm have been studied in a wide range of organic solvent. Specifically, these molecules are based on phenyl, furyl-, thienyl-oxazoles and oxadiazoles to compile a quasihomological series. Using the measured values of the extinction (epsilonabsν), the fluorescence quantum yields (γ), and the fluorescence lifetime (τ), we calculated rate constants for radiative decay (Kfl), and intercombination conversion (KST), along with the cross sections for absorption (σ13max), and stimulated emission (σ31osc). We also found the longest pump-pulse rise time (tlp) for which generate of oscillations active molecules. A broad spectrum of singlet and triplet electronic states using the semiempirical SCF MO LCAO method (Parr-Pariser-Pople, PPP/CI, a model approximation of π- electrons) and the complete and incomplete neglecting of differential overlap (CNDO/S-CI and INDO/S-CI, sp-electronic basis). In this paper, the photophysical parameters γ, τ, σ31osc, σ3S*, σ2T*, tlp, Kfl, KST, Elp (the threshold of the pump energy density) in the quasi-gomologicals series of complex active molecules are treated as depending on the structural factors in different ways. The physical mechanism responsible for the improvement in the photophysical properties of the mono-, three- and pentacyclic phenyl-, furyl-, and thienylbisoxazoles and oxadiazoles is established. The improvement is observed in the case when the separation of the bands of emission (σ31osc) and induced absorption on the S1* → Sn* (σ3S*) and T1 → Tn (σ2T*) transitions is maximum.