Molecular Rotors on Au(111): Rotator Orientation from IR Spectroscopy

Gold surfaces carrying altitudinal molecular rotors firmly attached through sulfur and/or mercury atoms have been examined by IR spectroscopy. The presence of an intact rotator has been confirmed and its average orientation with respect to the gold surface determined by single reflection thin-layer attenuated total reflection (ATR) spectroscopy, using metal surface selection rules. The requisite IR polarization directions were obtained from IR linear dichroism of a model rotator oriented in stretched polyethylene. The results are compatible with those of prior differential barrier height imaging measurements and molecular mechanics calculations.