Enhanced charge transfer in a monolayer of the organic charge transfer complex TTF–TNAP on Au(111)

Abstract

Electronic doping is a key concept for tuning the properties of organic materials. In bulk structures, the charge transfer between donor and acceptor is mainly given by the respective ionization potential and electron affinity. In contrast, monolayers of charge transfer complexes in contact with a metal are affected by an intriguing interplay of hybridization and screening at the metallic interface, determining the resulting charge state. Using scanning tunneling microscopy and spectroscopy, we characterize the electronic properties of the organic acceptor molecule 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) adsorbed on a Au(111) surface. The ordered islands remain in a weakly physisorbed state with no charge transfer interaction with the substrate. When the electron donor tetrathiafulvalene (TTF) is added, ordered arrays of alternating TNAP and TTF rows are assembled. In these structures, we find the lowest unoccupied molecular orbital (LUMO) of the free TNAP molecule shifted well below the Fermi level of the substrate. The TNAP is thus charged with more than one electron.

Electronic Structure of Titanylphthalocyanine Layers on Ag(111)

“…59,60 This interpretation was subsequently confirmed by density-functional theory (DFT) calculations. [61][62][63][64][65][66] In the meantime, additional molecules, e.g., NTCDA, 63 H 2 Pc and FePc 48 grown on Ag(111) and other substrates have been investigated, [67][68][69][70][71][72][73][74][75][76][77][78][79] which confirm the rather general phenomenon of the existence of interface states. Such a state can be successfully described by a model potential combining the metal substrate and a flat π-conjugated molecular layer.…”

Theoretical study of the adsorption of benzene on coinage metals

“…The adsorption of organic molecules on metals is of great interest since the formation of thin films and self-assembled monolayers opens the way toward a functionalization of surfaces [1–8]. The adsorbed molecules often contain an aromatic framework that can be substituted with functional groups.…”

Pronounced polarization-induced energy level shifts at boundaries of organic semiconductor nanostructures

“…Elucidating the exact structure and electronic properties at these boundaries requires nanometer scale probes that are difficult to apply to a full device structure. Recent studies using scanning tunnelling microscopy (STM) and spectroscopy (STS), alongside complementary techniques, on mixed donor–acceptor monolayers on metallic and semi-metallic surfaces have sought to characterize their electronic structure as model interfaces for organic photovoltaic materials 22 23 24 25 . In these examples, energy level shifts in the electronic states of both species arise from a combination of intermolecular and molecule-substrate interactions.…”