取代基及pH对水溶态多环芳烃荧光光谱特性影响

Influences of Substituents and pH on Fluorescence Characteristics of Water-Soluble Polycyclic Aromatic Hydrocarbons

利用三维荧光光谱法研究了不同pH(3~11)下水溶态(10μg·L^-1)的芘及1-羟基芘、1-氨基芘、1-甲基芘、1-芘甲酸、1-溴芘和1-硝基芘等6种含取代基多环芳烃(S-PAHs)的荧光光谱特性,探讨了取代基及溶液pH对7种PAHs的荧光光谱特征的影响规律。结果表明:取代基结构对芘环荧光峰及荧光信号存在不同影响,-OH,-NH 2,-CH 3,-COOH及-Br均可导致芘环激发波长和发射波长产生不同程度红移。与此同时,1-羟基芘和1-氨基芘的荧光强度高于芘,其原因是给电子基团-OH,-CH 3可增加芘环上共轭π电子云密度,进而降低分子基态激发能,增加分子的荧光效率;1-硝基芘和1-溴芘上的吸电子基团-NO 2及重原子取代基-Br具有强的诱导效应(-I),致芘环共轭体系中电子云密度降低,削弱分子的荧光效率;给电子基团-NH 2对芘环荧光强度影响并不明显,而吸电子基团-COOH小幅度增加芘环荧光效率。该实验条件下,pH对芘、1-甲基芘及1-溴芘的荧光峰位置及其荧光强度无显著影响;1-羟基芘最大荧光峰在pH=11时相比于pH≤9时发生红移,且荧光强度显著下降。pH对1-氨基芘和1-芘甲酸荧光光谱特性存在一定的影响,在pH=3时,-NH 2和-COOH发生质子化作用,使得1-氨基芘和1-芘甲酸荧光峰位置分别较pH≥5时发生蓝移和红移;1-氨基芘荧光强度在pH=3时略高于pH≥5,而1-芘甲酸荧光强度在pH=3时则略低于pH≥5。以上结果对水环境中S-PAHs荧光方法的建立及其原位测定有重要的意义。

In the range of pH at 3~11,the fluorescence spectra of water-soluble(10μg·L^-1)pyrene and substituted polycyclic aromatic hydrocarbons(S-PAHs)including 1-hydroxypyrene,1-aminopyrene,1-methylpyrene,1-pyrenecarboxylic acid,1-bromopyrene and 1-nitropyrene were measured by three-dimensional fluorescence spectroscopy.The influences of various substituents and solution pH on the fluorescence properties of seven kinds of PAHs were explored.The results showed that the fluorescence peak and fluorescence intensity of the pyrene ring were dependent on the substituent structure.The substituents of—OH,—NH 2,—CH 3,—COOH,and—Br can cause varying degrees of red shift in the excitation wavelength and emission wavelength of the pyrene ring.Meanwhile,the fluorescence intensities of 1-hydroxypyrene and 1-aminopyrene were higher than those of pyrene,which is mainly because the electron-donating group—OH,—CH 3 can increase the conjugatedπelectron cloud density on the pyrene ring,and then reduce the ground state excitation energy and increase the fluorescence efficiency of the fluorescence molecule.The electron-withdrawing group—NO 2 and heavy atom substituent—Br have a strong inductive effect,leading to decrease the electron cloud density on the pyrene ring conjugation system and reduce the fluorescence efficiency of the fluorescence molecule.The electron-donating group—NH 2 has no obvious effect on the fluorescence intensity of the pyrene ring,while the electron-withdrawing group—COOH could sluggishly increase the fluorescence efficiency of the pyrene ring.Under this experimental condition,there were no significant effects of pH on the fluorescence peak position and fluorescence intensity of pyrene,1-methylyrene and 1-bromopyrene.Compared with pH≤9,the maximum fluorescence peak of 1-hydroxypyrene was redshifted at pH=11,and the fluorescence intensity decreases significantly.In addition,the effects of pH on the fluorescence properties of 1-aminopyrene and 1-pyrenecarboxylic acid were also observed clearly.The fluorescence peaks of 1-aminopyrene and 1-pyrenecarboxylic acid were blueshifted and redshifted respectively,owing to the protonation effect at pH=3.The fluorescence intensity of 1-aminopyrene at pH=3 was slightly greater than that of pH≥5,while the fluorescence intensity of 1-pyrenecarboxylic acid at pH=3 was slightly lower than that of pH≥5.These studies are of great significance to the establishment of S-PAHs fluorescence analysis method and in situ determination of S-PAHs in the water environment.