The role of the interface in the electronic structure of adsorbed metal(II) (Co, Ni, Cu) phthalocyanines

Abstract

We compare the electronic structures of metal(II) (Co, Ni, Cu) phthalocyanines adsorbed on conducting and insulating substrates: Au(111) and the organic ferroelectric polyvinylidene fluoride (PVDF). The different 3d orbital contributions to the metal phthalocyanines result in different substrate interactions, and different molecular orbital offsets. When adsorbed on the ferroelectric PVDF surface, the photoemission and inverse photoemission spectra suggest that cobalt phthalocyanine (CoPc) bonds more strongly to both Au(111) and PVDF, resulting in a preferential planar configuration on the PVDF surface, not observed with nickel phthalocyanine (NiPc) and copper phthalocyanine (CuPc). A IntroductionFor molecular electronics, the energy level alignment is one of the key factors that determine charge injection and ultimately device performance. The electronic structure at an interface, be it metal-organic or molecular to molecular, is determined by a variety of competing and inter-related factors: adsorbate interactions, interface dipoles, charge transfer and molecular orientation and alignment. While large macrocyclic metalorganic and organometallic complexes tend to lie flat (that is to say with the long molecular axis parallel with the surface), like the metal phthalocyanines, this orientation is not always adopted at an interface. The metal phthalocyanines provide a means for exploring the influence of the center metal atom 3d filling on the molecular interactions at an interface, and thus provide an opportunity for investigating the interface interactions in a systematic fashion.For many large molecular adlayers, including a number of organic and metal-organic species, the energy level alignment of the adsorbate and the molecular orientation are dependent upon the interfacial electronic structure and the interfacial dipole layer. This influence of the interface has been readily demonstrated for many large molecules, 1-3 including the metal phthalocyanines. 4

Intermolecular bonding of hemin in solution and in solid state probed by N K-edge X-ray spectroscopies

“…Such a comparison of the XA spectra is presented in Figure 3 The most striking difference between the solid state and the solution spectra is the considerable broadening of almost all the spectral features in the solid state spectrum. This is likely due to the extensive orbital overlapping in the solid state [24,25] and was also somewhat evident in the previous study of aminobenzoic acid. [12] This solid state broadening makes the component A, originating from the N-Fe interaction as discussed in Figure 2, and component B resolvable in Figure 3a and 3b after the Gaussian fitting appear to be irresolvable in Figure 3c.…”

Isomeric effects with di-iodobenzene (C6H4I2) on adsorption on graphite

“…For many large molecule adlayers, including a number of organic and metal-organic species, the energy level alignment of the adsorbate with respect to a conducting substrate Fermi level or adjacent layer chemical potential is dependent on the interfacial electronic structure and interfacial dipole layer, as has been demonstrated for a number of molecules [1][2][3], including metal (II) macrocyclic compounds (MPc) [4][5][6][7][8][9][10][11][12]. For metal (II) phthalocyanines adsorbed layers, the d-filling of the metal center atom is seen to alter the molecular band offsets [6][7][8][9], and in the case of the macrocyclic metal tetraazaannulenes (TMTAA), the d-filling of the metal center atom alters the preferential molecular orientation upon adsorption [12].…”

“…For metal (II) phthalocyanines adsorbed layers, the d-filling of the metal center atom is seen to alter the molecular band offsets [6][7][8][9], and in the case of the macrocyclic metal tetraazaannulenes (TMTAA), the d-filling of the metal center atom alters the preferential molecular orientation upon adsorption [12]. For the roughly spherical closo-carboranes, a clear relationship is observed between the dipole moment of the adsorbate and the alignment of the observed molecular orbitals with respect the substrate Fermi level [3].…”

Occupied and unoccupied electronic structure of Na doped MoS2(0001)

“…In contrast, differences in the shifts seen for the unoccupied states (inverse photoemission) and occupied states (photoemission) are indicative of either final state effects or changes to the initial state band structure that lead to a closure of the band gap. Prior work attributed differences in the shifts seen for the unoccupied (inverse photoemission) and occupied states (photoemission) to final state effects 36,37 and frequently final state effects are most evident in the unoccupied state band structure. For molecular thin film systems, increased screening in the final state, affects more profoundly the inverse photoemission than the direct photoemission, leading to an apparent reduction in the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) gap.…”