同分异构体菲与蒽三维荧光特征的比较

Comparison of Three-Dimensional Fluorescence Characteristics of Two Isomers:Phenanthrene and Anthrancene

近年来三维荧光光谱法越来越多地用于研究环境领域污染物的迁移转化,但荧光光谱特征与物质分子结构的关系不清晰始终制约着应用。研究了典型的芳香族污染物同分异构体菲和蒽的荧光光谱特点。结果表明,菲和蒽有共同荧光峰λ_(ex)/λ_(em)=225/340 nm,且菲275/360 nm的荧光峰与蒽285/360nm峰位置也接近,然而两者荧光光谱仍存在明显差异。菲有3个清晰的荧光峰,在275/340 nm附近还有一峰,225/340 nm处的荧光最强。蒽的荧光光谱较复杂,250/380,250/400和250/425 nm附近荧光峰的强度较强。浓度为0.058 1 mg·L^(-1)时,共同荧光峰225/340 nm处蒽的荧光强度大约为菲的1.63倍。利用密度泛函理论的计算结果表明,蒽和菲的前线分子轨道能级差△E分别为3.621和4.779 eV。由于△E小和电子云的对称性好,蒽可在波长更长的激发光下发光且荧光强度更强。密度泛函理论可以用来判断有机物的发光能力。

In recent years, three-dimensional fluorescence spectrometry has been widely used to study the transportation and transformation of the environment pollutants. But little understanding about the relationship between fluorescence characteristics and molecular structure restricts its application. In the present paper, the excitation-emission matrix （EEM） of the typical aro- matic pollutants and isomers, phenanthrene and anthracene were studied. The result showed that there existed a peak locating atλex/λem=225/340 nm in the EEM of both phenanthrene and anthracene. Furthermore, the peaks at 275/360 ran of phenanthrene located quite close to the peak of anthracene at 285/360 nm. However, the difference between the EEM of phenanthrene and an- thracene was significant. There existed the third fluorescence peak at 275/340 nm and the most intensive peak at 225/340 nm in the EEM of phenanthrene. The EEM of anthracene was more complicated. The most intensive peaks located at ,tex/2cm = 250/ 38~）. 250/400 and 250/425 nm respectiveoy. In addition, the fluorescence intensity of anthracene at 225/340 nm was about l. 63 times that of phenanthrene when their concentrations were about 0. 058 1 rng ~ L-I. The orbital energy gap of the frontier mole- cules of phenanthrene and anthracene were 4. 779 and 3. 621 eV respectively according to the density functional theory, f3we to the smaller energy gap and better symmetry of electron cloud, anthracene was easier to be excited under the excitation of longer wavelength with higher fluorescence intensity. The density functional theory is a good tool to estimate the luminous capability of organic matters.