High resolution NEXAFS of perylene and PTCDI: a surface science approach to molecular orbital analysis

Abstract

We made use of synchrotron radiation to perform near edge X-ray absorption fine structure spectroscopy, NEXAFS, at the carbon K-edge of perylene and perylene-tetracarboxylic-diimide, PTCDI. Reference spectra measured for isolated molecules in the gas phase are compared with polarization dependent NEXAFS spectra measured on highly oriented thin films in order to study the symmetry of the molecular orbitals. The molecular overlayers are grown onto the rutile TiO 2 (110) surface for which the large anisotropic corrugation effectively drives the molecular orientation, while its dielectric nature prevents the rehybridization of the molecular orbitals. We employed density functional theory, DFT, calculations to disentangle the contribution of specific carbon atoms to the molecular density of states. Numerical simulations correctly predict the observed NEXAFS azimuthal dichroism of the s* resonances above the ionization threshold, from which we determine the full geometric orientation of the overlayer molecules. A discrepancy observed for the spectral contribution of the imide carbon atom to the calculated unoccupied molecular orbitals has been explained in terms of initial state effects, as determined by Hartree-Fock corrections and in full agreement with the corresponding shift of the C 1s core level measured by X-ray photoelectron spectroscopy, XPS.

TiO2(110) Charge Donation to an Extended π-Conjugated Molecule

“…In this case, we obtained an overall small CLS of both the N 1s (∼+0.6 eV) and the imide C 1s (∼−0.4 eV) with respect to that calculated for the neutral molecule. 29 Most importantly, the CLS shows opposite shift directions, contrary to experiments, thus excluding a simple molecular redistribution of the extracted charge.…”

Identifying On‐Surface Site‐Selective Chemical Conversions by Theory‐Aided NEXAFS Spectroscopy: The Case of Free‐Base Corroles on Ag(111)

“…Calculations of NEXAFS cross‐sections employing plane‐wave‐based DFT calculations have recently been reported by Fratesi et al. for rather symmetric, structurally planar molecules …”

“…[37,38] In such cases, predictive-quality calculations are not only extremelyh elpful, but are even required for the interpretation of the experimental data. In this context,d ifferent approaches, [39][40][41][42][43][44][45][46][47][48][49] based on, fore xample, band-structurec alculations, [40] constrained DFT calculations, [41] andc luster models, [42][43][44][45] have been appliedf or various surface-related molecular structures yielding reasonable agreement with experiment. Calculationso fN EXAFS cross-sectionse mploying planewave-based DFT calculations have recentlyb een reported by Fratesie tal.…”

“…for rather symmetric, structurallyp lanar molecules. [48,49] Herein, we have analyzed the on-surface chemistry of acomplex 2D moleculars ystem featuring multiple potential reaction sites and demonstrated that by combining angle-resolved NEXAFS information with high-level theoretical modeling the system's chemical conversions can be understoodatthe microscopic level. After fabricating ac ondensed, ultra-puret hin corrole film ((sub)monolayer regime) on the Ag(111)s urfacei n UHV at 200 K, we have taken reference X-ray absorption spectroscopy( XAS) spectra for the as-deposited low-temperature phase andt heir subsequent changes corresponding to the geometries of the singly dehydrogenated molecules (annealed to 330 K, 2H-TpFPC·)a nd apparently ring-closed species( annealed to 430 K, 2H-TpFPC·(rc)).…”

Valence electronic structure of sublimated Fe4single-molecule magnets: an experimental and theoretical characterization

“…[28][29][30] There are few DFT studies on Fe 4 propeller-like clusters already present in the literature. [28][29][30] There are few DFT studies on Fe 4 propeller-like clusters already present in the literature.…”