作者:J. Jayabharathi、V. Thanikachalam、K. Brindha Devi、M. Venkatesh Perumal
DOI:10.1007/s10895-011-1009-x
日期:2012.3
Some novel Y-shaped imidazole derivatives were developed and characterized by NMR and mass spectral techniques. The photophysical properties of these imidazole derivatives were studied in several solvents. The Kamlet-Taft and Catalan’s solvent scales were found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The adjusted coefficient representing the electron releasing ability or basicity of the solvent, C β or C SB has a negative value, suggesting that the absorption and fluorescence bands shift to lower energies with the increasing electron-donating ability of the solvent. This effect can be interpreted in terms of the stabilization of the resonance structures of the chromophore. The observed lower fluorescence quantum yield may be due to an increase in the non-radiative deactivation rate constant. This is attributed to the loss of planarity in the excited state provided by the non co-planarity of the cinnamaldehyde ring attached to C(2) atom of the imidazole ring. Such a geometrical change in the excited state leads to an important Stokes shift, reducing the reabsorption and reemission effects in the detected emission in highly concentrated solutions.
开发了一些新颖的Y型咪唑衍生物,并通过NMR和质谱技术对其进行了表征。在多种溶剂中研究了这些咪唑衍生物的光物理性质。研究发现,Kamlet-Taft和Catalan的溶剂标尺最适合描述吸收和荧光发射的溶剂化色移。代表溶剂电子释放能力或碱性的调整系数C β或C SB为负值,表明随着溶剂给电子能力的增强,吸收和荧光谱带向低能方向移动。这一效应可以用发色团共振结构的稳定化来解释。观察到的较低的荧光量子产率可能是由于非辐射失活速率常数的增加。这归因于咪唑环C(2)原子连接的肉桂醛环非共平面性在激发态中导致的平面性损失。这种激发态的几何变化导致重要的斯托克斯位移,减少了在高浓度溶液中的再吸收和再发射效应。