Effect of fluorine substitution on the electronic states and conductance of CuPc on Cu(100)

Abstract

The electronic states and conductance of CuPc, F₈CuPc, and F₁₆CuPc on Cu(100) were studied by using scanning tunneling microscopy (STM) and the density functional theory (DFT) calculations. For all molecules, the lowest unoccupied molecular orbital (LUMO) was observed around the Fermi level (E_F), regardless of the difference in the original LUMO levels of the free molecules. This indicates that the strong interaction causes the pinning of E_F at LUMO levels. Meanwhile, the differential conductance at E_F is drastically affected by the substitution: it increases and decreases for CuPc and F₁₆CuPc, respectively, suggesting that the Fano effect plays a major role in the conductance. This finding provides a new strategy for the control of molecular conductance by chemical substitution.