Herein, we report the synthesis of a double hydrazone capable of undergoing photochemical E/Z isomerization through the imine double bonds. The bis(hydrazone) 1-E,E can be considered as a "two-arm" system in which the controlled movement of each arm is obtained by photo-modulation, making possible the appearance of two isolable metastable isomeric states 1-E,Z and 1-Z,Z. Such states are characterized by very specific structural, optical, and electrochemical properties. The latter allows the reversible return from either 1-E,Z or 1-Z,Z to the 1-E,E state. Our results are of great importance in the further development of molecular machines and photochemically controlled reactions by introducing for the first time double hydrazones as tunable photochemical switches.
The [3 + 2] cycloaddition reaction of C 60 with pyridine-derived hydrazones (acting as dipolar reagents) was successfully conducted resulting in fullerene derivatives 5a-b. The compounds were characterized by means of NMR, UV-Vis spectroscopy, and X-ray crystallography. The electrochemical behavior was also investigated. The fulleropyrazoline 5a exhibits anodically shifted reduction potentials of about 100 mV when compared with those for C 60 , whereas 5b exhibits cathodic shifts relative to pristine C 60 . The complexation reaction of 5b with metallic ions (Zn 2+ , Cd 2+ , and Fe 2+ ) was achieved. Job and Benesi-Hildebrand analysis confirmed the formation of complexes with a molar ratio of 1:1 and binding constants between 2.26 × 10 5 and 1.59 × 10 5 M À1 . Electrochemistry of these complexes showed a marked influence of the metal ion on the reduction potentials.
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