Cocrystals align semiconductor building blocks

To get the most out of organic semiconductors, it's important to maximize the face-to-face π-stacking of the aromatic groups in their building blocks. But the intermolecular forces that scientists rely upon to orient the molecules-van der Waals and dipole-dipole interactions-are fairly weak. University of Iowa chemists Leonard R. MacGillivray, Anatoliy N. Sokolov, and Tomislav Frii have developed a different strategy: They rely on cocrystals to clamp the molecules into place via slightly stronger hydrogen bonds (J. Am. Chem. Soc., published online Feb. 11, dx.doi.org/10.1021/ja057939a). The researchers functionalized the semiconductor building blocks thiophene and anthracene with 4-pyridylacetylene handles and then cocrystallized the molecules with a resorcinol derivative. In the structure shown, resorcinol's two hydroxyl groups (red) hydrogen bond with the nitrogen atoms (blue) on the pyridylacetylene handles, thereby forcing a face-to-face interaction between the central anthracene groups. MacGillivray says the approach could, in principle, be used "to order any semiconductor molecule to exhibit face-to-face stacking in the solid state."