Abstract: 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 5.85×10⁵ 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.