Photophysical properties of trans-1-(3-trans-stilbenyl)-2-pyrazinylethylene and microviscosity of AOT reversed micelle

Abstract

The absorption spectra of trans-1-(3-trans-stilbenyl)-2-pyrazinylethylene(SbPyE) shows as like summation of stilbene(St) and styrytlpyrazine(StPy) because SbPyE is cross-conjugated in the ground state, therefore, St and StPy moieties absorbe light independently. The fluorescence spectra of 1:1 mixture of St and StPy varied greatly upon changing the excitation wavelength because of molar absorption coefficient differences of St and StPy at given excitation wavelengths. But, the fluorescence spectral shape of SbPyE unchanged upon changing the excitation wavelength in ethanol and various other solvents. It is attributed to the energy transfer between the cross-conjugated bichromophore(St, StPy) in the excited states. In this case emission state has StPy moiety character. The fluorescence quantum yields of StPy increase dramatically with increasing solvent polarity. On the contrary, the fluorescence quantum yields of SbPyE increased dramatically from n-hexane to methylenechloride and then decreased with increasing solvent polarity in more polar solvents than methylenechloride. This result probably comes from conformational equilibrium change in various solvents and these conformers probably have similar fluorescence spectral shapes with different emission intensities. It was observed from n-hexane solutions on addition of increasing amounts of ethanol and from thermodynamic control in methylcyclohexane and 2-methyltetrahydrofuran with decreasing temperature. Also, supporting data were obtained from fluorescence lifetime measurements by single photon counting method. Microviscosity around the water pool generated in Aerosol-OT/hexane/water reversed micelle solutions was studied by monitoring the depolarization of solubilized probe fluorescence. The probe, SDU, used in this study was moderately polar and was proved to be solubilized between interface and hydrocarbon phase in reversed micelle solution by fluorescence quenching study with hydrophilic and hydrophobic qu...