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.