Dihydroazulene–Buckminsterfullerene Conjugates

The dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch has recently attracted interest as a molecular switch for molecular electronics. In this field, Buckminsterfullerene, C₆₀, has been shown to be a useful anchoring group for adhering a molecular wire to an electrode. Here we have combined the two units with the overall aim to elucidate how C₆₀ influences the DHA–VHF switching events. Efficient synthetic protocols for making covalently linked DHA-C₆₀ conjugates were developed, using Prato, Sonogashira, Hay, and Cadiot–Chodkiewicz reactions. These syntheses provide as well a variety of potentially useful DHA and C₆₀ building blocks for acetylenic scaffolding. The two units were separated by bridges of various lengths, such as oligo­(phenyleneethynylene) (OPE2 and OPE3) wires. The distance of separation was found to influence strongly the light-induced ring-opening reaction of DHA to its corresponding VHF. Thus, C₆₀ was found to significantly quench this conversion when situated closely to the DHA unit