| Research Abstract |
The radial stepwise complexation was also observed for the other dendrimers with phenylazomethine dendron skeletons. With all dendrimers, a four-step shift of the isosbestic point was observed with gradual addition of stannous chloride. In DPA G4 with a triphenylamine core, the shifts occur after the addition of 3, 6, 12, and 24 equivalents of SnCl_2. In DPA with a porphyrine core, the shifts occur after the addition of 4, 8, 16, and 32 equivalents. In the aniline-capped DPA G4 dendron, the shifts occur after the addition of 1, 2, 4, and 8 equivalents. In each dendrimer, the amounts of SnCl_2 added to the solution agree with the number of imines in the 1^<st> to 4^<th> shells. These results support that the complexation in DPA derivatives proceeds from the core imines to the terminal ones. The basicity of the inner imines is enhanced by the electron-releasing effect of the outer imines, and the stepwise complexation is caused by the different basicity of the imines between the shells. This complexation behavior means that the number and the position of the metal ions in the dendrimers are controllable.
During the complexation of DPA-F G2 with SnCl_2, two shifts in the isosbestic point appeared on adding 0-4 and 5-6 equivalents of SnCl_2 in the UV-vis spectra. This result shows that the imines present in the 2^<nd> shell were complexed first and then those present in the 1^<st> shell, whose basicity was lowered by the electron-withdrawing group. On adding SnCl_2 to DPA-F G3, three shifts of the isosbestic point appeared upon adding 0-4, 5-12, and 13-14 equivalents of SnCL_2. That is, the imines present in the 2^<nd> shell were complexed first, then those present in the 3^<rd> shell, and finally those present in the 1^<st> shell.
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