FePc and FePcF16 on Rutile TiO2(110) and (100): Influence of the Substrate Preparation on the Interaction Strength

Solution Adsorption of Fluorinated Zinc Phthalocyanines on Titania: Combined XPS, UV-Vis, and Contact Angle Study

The equilibrium solution adsorption of perfluorinated metal phthalocyanines F_XPcZn (x = 16, 64) on titania was investigated. This method was explored as an alternative to the frequently used vapor deposition technique for the preparation of solid-supported phthalocyanines for applications such as sensitizers, catalysts, and sensors. According to X-ray photoelectron spectroscopy (XPS), UV-vis, and water contact angles, the adsorption of phthalocyanines from acetone solution occurred readily at room temperature resulting in the formation of hydrophobic surfaces of the solid-supported phthalocyanines. The adsorption isotherms (298 K) were of the Langmuir-type with saturation plateau. The effective thickness of the adsorbed layers at the plateau regions was estimated at 0.17 nm (F₁₆PcZn) and 0.47 nm (F₆₄PcZn), which, assuming the face-down orientation of phthalocyanines, corresponded to ∼52 and ∼77% of the complete monolayers, respectively. In the case of F₆₄PcZn, the state of the adsorbed molecules was similar to that of bulk F₆₄PcZn, suggesting only weak adsorption interactions of dispersive type. In contrast, F₁₆PcZn showed strong interactions with the surface of titania including the dissociation of C-F bonds, i.e., chemisorption. The difference in the adsorption interactions of F₁₆PcZn vs F₆₄PcZn was attributed to the presence of eight i-C₃F₇ groups decorating the perimeter of the F₆₄PcZn molecule. These bulky substituents in the peripheral positions sterically protected the nonperipheral fluorine atoms, thereby preventing their substitution and any other specific interactions between the macrocycle and the surface OH groups.

Interface Properties of CoPc on Nanographene-Covered Au(111) and the Influence of Annealing

Organic bilayer systems and heterostructures are of enormous importance for optoelectronic devices. We study interface properties and the structural ordering of cobalt phthalocyanine (CoPc) on a highly ordered monolayer hexa-peri-hexabenzocoronene (HBC), grown on Au(111), using photoemission, X-ray absorption, scanning tunneling microscopy, and low-energy electron diffraction. A charge transfer between CoPc and the gold substrate is almost completely prevented by the HBC intermediate layer. We show that HBC acts as a template for the initial growth of CoPc molecules. After annealing to 630 K, a molecular exchange takes place, resulting in a coexistence of domains of both CoPc and HBC molecules on the surface.

Substrate mediated interaction of terbium(III) double-deckers with the TiO2(110) surface

A terbium(iii)-bis(phthalocyaninato) neutral complex was deposited on the rutile TiO2(110) surface, and their interaction was studied by Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). It was found that the TiO2 rutile surface favours the adsorption of isolated molecules adopting a lying down configuration with the phthalocyanine planes tilted by about 30° when they lie in the first layer. The electronic and chemical properties of the molecules on the surface were studied by XPS as a function of the TiO2(110) substrate preparation. This study evidences that strong molecule-substrate interactions are present and a charge transfer process occurs from the molecule to the surface.

Interface interaction of transition metal phthalocyanines with strontium titanate (100)

We study interface properties of CoPcF x and FePcFx (x = 0 or 16) on niobium-doped SrTiO3(100) surfaces using mainly X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. For all studied molecules, a rather complex, bidirectional charge transfer with the oxide substrate was observed, involving both the macrocycle and the central metal atom. For molecules of the first monolayer, an electron transfer to the central metal atom is concluded from transition metal 2p core level photoemission spectra. The number of interacting molecules in the first monolayer on the oxide surface depends on the central metal atom of the phthalocyanine, whereas the substrate preparation has minor influence on the interaction between CoPc and SrTiO3(100). Differences of the interaction mechanism to related TiO2 surfaces are discussed.

The interface between chloroaluminum phthalocyanine and titanium dioxide: the influence of surface defects and substrate termination

Interface properties of chloroaluminum(iii) phthalocyanine (AlClPc) on two different rutile titanium dioxide (TiO2) single crystal surfaces ((100) and (001)) have been studied using X-ray and ultraviolet photoemission spectroscopy (XPS and UPS). It is shown that the strength of the interaction clearly depends on the substrate termination and preparation. Generally, the (001) surface is more reactive compared to the (100) surface. The most important interaction channel involves the nitrogen atoms of the phthalocyanine macrocycle. An exposure to oxygen during the annealing steps of the preparation procedure allows diminishing the extent of interaction of nitrogen with titanium dioxide. The work function of AlClPc/TiO2 is rather independent of the substrate, indicating a pinning regime at all interfaces, where the HOMO of the molecule is aligned at the maximum of the defect states of the substrate.