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.

Key words: nitryl zinc porphyrin, imidazole derivatives, axial coordination reaction, thermodynamic properties, fluorescence spectrum