光谱法研究硝基苯基卟啉锌与咪唑类的轴向配位反应

Axial Coordination Reaction Between Nitryl Phenyl Zn Porphyrin and Imidazole Derivatives Studied by Spectroscopic Method

采用紫外-可见光谱滴定法和荧光光谱法,考察了5-对硝基苯基-10,15,20-三苯基锌卟啉和5-邻硝基苯基-10,15,20-三苯基锌卟啉与3种咪唑类客体小分子进行轴向配位反应的光谱性质,并探讨取代基团在不同位置时的锌卟啉及具有不同结构特点的客体对该类轴配反应进行的影响。实验结果表明,2种锌卟啉与咪唑类客体之间的轴配反应是按摩尔比1:1进行,轴配反应的平衡常数均按K(2-MeIm)>K(N-MeIm)>K(Im)顺序依次减弱,其中5-邻硝基苯基-10,15,20-三苯基锌卟啉与2-甲基咪唑间的轴配反应有最大的平衡常数5.85×105L/mol。轴配反应的平衡常数均随温度的升高而降低,温度升高不利于平衡反应的进行。热力学参数表明,这类反应的驱动力是焓驱动,是自发进行的配位反应。随客体浓度的增加,5-对硝基苯基-10,15,20-三苯基锌卟啉(荧光峰位:592.9、634.2nm)与咪唑类客体的轴配体系具有荧光增强的效应,5-邻硝基苯基-10,15,20-三苯基锌卟啉(荧光峰位:583.6、629.8nm)与咪唑类客体的轴配体系具有荧光猝灭的效应。轴配体系的荧光效应是由锌卟啉中硝基基团的位置所决定的,而与客体的结构特点无关。

The spectroscopic properties of coordination reactions between two Zn prophyrin [5-（p-nitrylphenyl）-10,15,20-triphenyl Zn porphyrin and 5-（o-nitrylphenyl）-10,15,20-triphenyl Zn porphyrin] and three imidazole（Im） derivatives were studied by means of UV-Vis spectroscopy titrations and fluorescence spectroscopy.The axial coordination reactions were related to different positions of substituent group in Zn prophyrin and the structure of guest.The results show：the axial coordination reaction was carried out in a molar ratio of 1∶1,the association constants decreased in the order of K（2-MeIm）〉K（N-MeIm）〉K（Im）,in which the maximum association constant was 5.85×10^5 L/mol between 5-（o-nitrylphenyl）-10,15,20-triphenyl Zn porphyrin and 2-MeIm;the association constant would decrease with increasing temperature,which was a disadvantage factor for the reaction;the thermodynamic parameters revealed that the driving force was the change of enthalpy and the reaction was spontaneous;the intensity of fluorescence increased in the system of axial coordination reaction of 5-（p-nitrylphenyl）-10,15,20-triphenyl Zn porphyrin（fluorescence peak：592.9 nm,634.2 nm） with increasing the guest concentration,and the fluorescence quenching exhibited in the system of axial coordination reaction of 5-（o-nitrylphenyl）-10,15,20-triphenyl Zn porphyrin（fluorescence peak：583.6 nm,629.8 nm）.The fluorescence effect was determined by the position of nitryl group in Zn prophyrin and independent of the structure of guest.