不同取代基对苯系物三维荧光光谱特征的影响

采用F-7000荧光光谱仪分别研究了14种苯系物在不同浓度时的三维荧光光谱特征，探讨了各物质三维荧光光谱特征与其结构特性之间的关系。结果表明：苯环上取代基的结构、位置及数量均会影响苯系物的荧光特征。其中苯、甲苯、乙苯、丙苯、异丙苯、二甲苯、均三甲苯荧光峰λ_ех/λ_еm=205~215 nm/280~295 nm；苯乙烯荧光峰λ_ех/λ_еm=230/345 nm；苯酚的两个荧光峰λ_ех/λ_еm=220/300和270/295 nm；苯胺两个荧光峰λ_ех/λ_еm=235/335和280/335 nm；氯苯有一个荧光峰λ_ех/λ_еm=215/290 nm；硝基苯无明显荧光信号。由于甲基、乙基等烷基与苯环直接相连的碳原子扩大了苯环刚性平面，1 mg·L-1浓度条件下，与苯相比较：甲苯和乙苯的荧光强度FI分别增强了10.62和9.45倍，λ_ех红移5 nm；对二甲苯、三甲苯、间二甲苯、邻二甲苯的FI增强倍数分别为5.49，4.87，2.14和1.33，说明烷基类取代基中与苯环共面、非共面碳原子的数量都会影响物质的荧光特性。苯乙烯的乙烯基团扩大刚性平面的同时，不饱和双键降低了其激发所需能量，苯乙烯浓度为0.002 mg·L-1的荧光强度与10 mg·L-1的乙苯荧光强度相当，λ_ех相对乙苯红移了20 nm。给电子基团-OH和-NH₂对苯环荧光强度的影响介于烷基与不饱和键之间，其n电子与苯环π体系形成了P-π共轭结构，刚性平面扩大，荧光强度增强，荧光光谱红移；含得电子基团-NO和-Cl类物质的n→π₁*跃迁属于禁戒跃迁，产生的激发态分子数较少，同时系间窜越作用强于π₁*→S₁，理论上荧光较弱或不发荧光，实验结果与理论一致。

Effects of Different Substituents on Three Dimensional Fluorescence Properties of BTEX

Three-dimensional fluorescence excitation-emission has been widely used to characterize dissolved organic matter in municipal wastewater ,lakes and rivers .However ,As one of the most important pollutants in petrochemical wastewater ,the fluorescence characteristics of BTEX are rarely reported .In this paper ,the fluorescence spectra of 14 typical BTEX at different concentrations were studied by F-7000 fluorescence spectrometer ,and the relationship between the characteristics of three di-mensional fluorescence spectra and their structural characteristics was discussed .The results showed that the structure ,location and number of the substituents will affect the fluorescence characteristics of BTEX .Fluorescence peaks of benzene ,toluene ,eth-yl-benzene ,n-propylbenzene ,cumene ,xylene and 1 ,2 ,4-trimethyl benzene located at λех/λеm =205~215/280~295 nm .A fluo-rescence peak of styrene located at λех/λеm =230/345 nm .Two fluorescence peaks of phenol located at λех/λеm =220/300 nm , 270/295 nm .Two fluorescence peaks of aniline located at λех/λеm =235/335 nm ,280/335 nm .Chlorobenzene had a fluorescence peak locating at λех/λеm =215/290 nm ,and no obvious fluorescence peaks of nitrobenzene were found .On the conditions of 1 mg · L -1 compared with benzene ,the fluorescence intensity (FI) of toluene and ethylbenzene were increased by 10.62 and 9.45 times ,with λех red shifting 5 nm ,and intensity of fluorescence peaks of 1 ,2 ,4-trimethylbenzene ,three kinds of xylene enhance-ment ratio were 5.49(above) ,4.87 ,2.14 ,1.33 .This is mainly due to the carbon atoms of substituents which directly connect-ed with benzene-ring expanded the rigid plane .This showed the number of carbon atoms that non coplanar and coplanar of alkyl substituents in benzene will affect the fluorescence properties of matter .When the vinyl group of styrene expanded the rigid plane ,the unsaturated double bond reduced the energy required for its excitation ,the fluorescence intensity of 10 mg · L -1 eth-ylbenzene same with the concentration of 0.002 mg · L -1 styrene ,the λех red shifting 20 nm compared with ethylbenzene rela-tively .Electron donating substituents ,—O H and —N H2 can enhance the electron density of conjugated structure of the benzene-ring .The P orbital of n electron with the benzene formation of P—πconjugated system structure ,rigid plane expansion ,the in-tensity of fluorescence peaks increased with fluorescence spectrum redshift .On the contrary ,the —NO2 and —Cl groups sub-stances n→π* transition belonged to the forbidden transition ,the less number of excited state molecules ,while the intersystem crossing was stronger thanπ* → S1 .Experimental results for weak fluorescence or no fluorescence were consistent with the theo-ry .