Intramolecular structure and intermolecular packing in crystalline molecular semiconductors should have profound effects on the charge-carrier wave function, but simple drift mobility measurements are not very sensitive to this. Here we show that differences in the Hall resistance of two soluble pentacene derivatives can be explained with different degrees of carrier delocalization being limited by thermal lattice fluctuations. A combination of Hall measurements, optical spectroscopy, and theoretical simulations provides a powerful probe of structure-property relationships at a molecular level.

1,4,8,11-Methyl-substituted 6,13-triethylsilylethynylpentacene shows extended pi-pi overlap when deposited from solution, yielding organic thin film transistors with high and reproducible hole mobility with negligible hysteresis.