Theoretic and Experimental Study of Photoprocesses in Substituted 4-Dicyanomethylene-4H-pyrans

Abstract

1 Substituted 4-dicyanomethylene-4H-pyran (DCM) derivatives are widely used in quantum electronics and optoelectronics as active media of tunable lasers, emitting layers of organic light diodes [1,2], and nonlinearoptics media [3][4][5]. The active media based on substituted DCMs lase in the red spectral region in solutions and solid matrices [6,7], have high photochemical stability, and exhibit a broad emission band up to 120 nm. Their absorption and emission spectra practically do not overlap (the Stocks shift attains 160 nm). This makes it possible to obtain the high efficiency of emission conversion in both the transverse and longitudinal modes of excitation. Reabsorption losses are low even at high concentrations of active molecules.Some DCMs possess nonlinear optical properties. Recently, we have shown [8] that substituted DCMs attenuate the emission of the Nd-YAG laser second harmonics, but their attenuation coefficient ranks below that of fullerenes and polymethine or phthalocyanine dyes.The aim of this work was to study the photoprocesses occurring in the molecules of substituted DCMs and to reveal the effect of the molecular structure on their spectral and luminescent parameters. EXPERIMENTALThe structural formulas of the 4-dicyanomethylene-4H-pyrans under study are given below.The quantum-chemical study of photoprocesses occurring in these molecules was performed by the INDO/S method with the use of an original software package [9]. The use of this method allows us to build the complete scheme of electronically excited states of molecules, to calculate their dipole moment, oscillator strength, charge distribution in molecules, and the spec-1 e-mail:svet@elefot.tsu.ru tra of induced absorption from excited triplet and singlet states. The use of the theory of nonradiative transfer of the energy of electronic excitation in a molecule makes it possible to estimate the rate constants of deactivation processes [10], to establish their trends depending on the molecular structure, and to predict the molecular structures with given properties.The experimental studies of the photoprocesses in DCM were carried out with the use of a Specord M40 spectrophotometer and a Hitachi 85 spectrofluorimeter. The fluorescence quantum yield of the molecules was determined relative to Rhodamine C in ethanol ( γ = 0.65) according to the procedure described in [11].Ethyl acetate, ethanol, and dimethyl sulfoxide (DMSO) were used as solvents. Their purity was controlled by spectrophotometry. The concentration of the molecules under study was 10 -4 (in recording absorption spectra) and 10 -6 -10 -5 mol l -1 (in recording the spectra and measuring the quantum yields of fluorescence).Substituted DCMs under study were synthesized by Ponomareva O.V. (Dolgoprudnyi, NPF DELTAKOR) and were used without additional purification. RESULTS AND DISCUSSIONExperimental and calculated positions of the absorption band maximums of substituted DCM under study are listed in Table 1. Note that the experimental data agree well with the results obtained ...

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