Phthalocyanine aggregates on metal dichalcogenide surfaces: dye sensitization on tin disulfide semiconductor electrodes by ordered and disordered chloroindium phthalocyanine thin films

Iron near absorption edge X-ray spectroscopy at aqueous-membrane interfaces

Employing synchrotron X-ray scattering, we systematically determine the absorption near-edge spectra (XANES) of iron in its ferrous (Fe(2+)) and ferric (Fe(3+)) states both as ions in aqueous solutions and as they bind to form a single layer to anionic templates that consist of carboxyl or phosphate groups at aqueous/vapor interfaces. While the XANES of bulk iron ions show that the electronic state and coordination of iron complexes in the bulk are isotropic, the interfacial bound ions show a signature of a broken inversion-symmetry environment. The XANES of Fe(2+) and Fe(3+) in the bulk possess distinct profiles however, upon binding they practically exhibit similar patterns. This indicates that both bound ions settle into a stable electronic and coordination configuration with an effective fractional valence (for example, Fe([2+ν]+), 0 < ν < 1) at charged organic templates. Such two dimensional properties may render interfacial iron, abundant in living organisms, a more efficient and versatile catalytic behavior.

Self-assembling of zinc phthalocyanines on ZnO (1010) surface through multiple time scales

We adopt a hierarchic combination of theoretical methods to study the assembling of zinc phthalocyanines (ZnPcs) on a ZnO (1010) surface through multiple time scales. Atomistic simulations, such as model potential molecular dynamics and metadynamics, are used to study the energetics and short time evolution (up to ∼100 ns) of small ZnPc aggregates. The stability and the lifetime of large clusters is then studied by means of an atomistically informed coarse-grained model using classical molecular dynamics. Finally, the macroscopic time scale clustering phenomenon is studied by Metropolis Monte Carlo algorithms as a function of temperature and surface coverage. We provide evidence that at room temperature the aggregation is likely to occur at sufficiently high coverage, and we characterize the nature, morphology, and lifetime of ZnPc's clusters. We identify the molecular stripes oriented along [010] crystallographic directions as the most energetically stable aggregates.

Optical differential reflectance spectroscopy of ultrathin epitaxial organic films

This Perspective does not have the ambition to entirely review the subject of optical spectroscopy on thin organic films. What we will try to achieve instead is to give an overview on optical reflectance spectroscopy of highly ordered organic thin films in the thickness range from submonolayers to several monolayers, as a tool to study the absorption behavior of such films. By doing so, we will emphasize the relations between the physical layer structure and the resulting optical properties. More specifically, we intend to show on the basis of particular examples what physical effects can be favorably examined by means of real-time optical spectroscopy, i.e., applied during the actual film growth, especially differential reflectance spectroscopy (DRS). Epitaxial organic films on inorganic substrates (insulators and conductors) will be in focus, and also the perspectives of investigating organic-organic heteroepitaxial layers will be addressed.

Ultraviolet-visible and surface-enhanced Raman scattering spectroscopy studies on self-assembled metalloporphyrin films on organic monolayer-modified ultra-thin silver substrates

A self-assembled monolayer (SAM) film of 5,10,15,20-tetra-(para-chlorophenyl)-porphyrin terbium (or lutetium) hydroxy compound (TbOH/LuOH) fabricated on a silver substrate premodified with a SAM of 4-mercaptopyridine (PySH) was studied by ultraviolet-visible (UV-Vis) spectroscopy and surface-enhanced Raman scattering (SERS) spectroscopy. PySH can modify the substrate and deliver its pyridyl group pointing out from the silver surface. Thus, we can investigate the effects of the central metals of the metalloporphyrins in the formation of the composite films. For the TbOH-PySH composite film, a new absorption band arising from TbOH appears at 425 nm, and a band at 512 nm due to the PySH-modified silver substrate shifts to a longer wavelength (538 nm). The results suggest that TbOH is successfully assembled on the top of PySH-modified silver film and that there is an interaction between TbOH and PySH in the film. The frequency shifts and relative intensity changes of bands due to PySH in the SERS spectra imply the coordination of the pyridyl group on Tb in the SAM. As for the LuOH-PySH composite film, its SERS spectrum shows bands arising from both the LuOH and PySH moieties, indicating that LuOH is assembled on the PySH-modified silver film. Furthermore, a band at 1221 cm(-1) due to the in-plane C-H bending mode of PySH disappears, implying that the pyridyl moiety of PySH becomes more parallel to the silver surface upon the formation of the LuOH-PySH composite film. Additionally, an absorption band at 515 nm shifts to a longer wavelength (541 nm) and becomes broad upon the formation of the composite film, suggesting an interaction between LuOH and PySH in the film. By comparing the spectral changes between the two self-assembled composite films, we find that the central metal is crucial in the formation of the composite films. The structure and orientation of the composite films depend on the central metal of the metalloporphyrin compounds.