A local view on hyperconjugation

Two isomers of the methylterrylene molecule were adsorbed on a NaCl bilayer deposited on Cu(1 1 1) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5 K). The images acquired for specific bias voltages show a striking similarity with the spatial distribution of the electronic probability density in the highest occupied molecular orbital (HOMO) and in the lowest unoccupied molecular orbital (LUMO) of free methylterrylene. They are well reproduced by elastic scattering quantum chemistry calculations. These data provide a direct view of the hyperconjugative interaction between the methyl group and the frontier orbitals of terrylene.