The deposition and characterization of molecular-sized rotors on gold and glass surfaces

Altitudinal (axle parallel to surface) molecular rotors have previously been synthesized with two different types of attachment functionalities suitable for either gold or glass surfaces. These were in the form of "tentacles" attached to the rotor through Hg atoms. For gold, the rotor was designed to benefit from the high affinity dialkyl sulfides have for self-assembly. XPS data indicate that the sulfur containing tentacles oxidized within hours of exposure to air and were lost; the rotor nevertheless remained firmly attached, apparently due to the interaction of the Hg atoms with the gold. The surfaces have been characterized by ellipsometry, IR and XPS spectroscopy, and scanning tunneling microscopy. The average orientation of the rotor dipole on gold was determined using Attenuated Total Reflection Spectroscopy in conjunction with Linear Dichroism Infrared Spectroscopy (LD-IR). Trialkoxysilane containing tentacles were used to deposit the rotors onto glass surfaces so that the dynamics of thermally activated dipole motion could be investigated with dielectric spectroscopy. Both polar and non-polar versions of the rotors produced a dielectric response, an unexpected result. It is believed the dipole motion originates from rotation of the cyclopentadienyl ring to which the tentacles are attached in the rotors.