m-Carborane thiols, jointly developed by our Materials Science and Pennsylvania State University, represent a new family of cage-like molecules suitable for designing self-assembled monolayers (SAMs) with stable and controllable geometries.1
m-Carborane-1-thiol (M1) H atoms omitted for clarity Cat. No. 695572
m-Carborane-9-thiol (M9) H atoms omitted for clarity Cat. No. 686506
Experiments performed on two different materials, m-Carborane-1-thiol(M1) and m-Carborane-9-thiol(M9), revealed their ability to form SAMs with identical geometries (Figure 1) but different sets of properties such as chemical resistance and wettabilitity.2
Figure 1. Scanning tunneling microscope images of carboranethiol SAMs (M1 (left), M9 (middle), and mixed (right)) all have the same lattice. Reproduced from ref. 2 with permission from the American Chemical Society.
In addition, the M1 molecules form more stable SAMs than their M9 analogs. This effect can be attributed to stronger dipole-dipole interactions between the polar M1 clusters as compared to the less polarized M9 cages (Figure 2). As a result, more energy is required to remove an M1 molecule from the SAM.
Figure 2. Schematic showing relative dipole orientations for the carboranethiol isomers, M1 and M9.1 The M1 molecule's dipole is oriented nearly parallel to the surface of the SAM, while the M9 molecule's dipole is oriented perpendicular to the surface of the SAM. The arrows point in the direction of positive charge. Hydrogen atoms omitted for clarity. Reproduced from ref. 2 with permission from the American Chemical Society.