Tunneling through nanographene stacks

We present a scanning tunneling microscopy STM and spectroscopy STS study of a nanographene, hexa-peri-hexabenzocoronene HBC, in different stacked geometries, covalently bound in cyclophanes or physisorbed in double layers consisting either of HBCs only or of a mixture of HBC and an alkylated disk-type electron acceptor, coronenediimide. Tunneling bias-dependent STM and STS at the solid-liquid interface reveal that the lateral offset between the stacked molecules strongly influences the electron transport through the stacks, which is attributed to different highest occupied and lowest unoccupied molecular orbital splittings in the stacks. The results imply that the control over the stacking in nanographene multilayers or columns can be used to control their electron transport properties.