Simulation of X-ray Absorption Near Edge Spectra of Organometallic Compounds in the Ground and Optically Excited States

Abstract

The Mg K-edge and Zn K- and L3-edge X-ray absorption near edge spectra of Mg and Zn porphyrins in the ground state and low-lying optically excited states are calculated. Also computed are X-ray absorption near edge spectra of Fe(II) spin crossover compound in its ground and low-lying optically excited states, motivated by a recent experiment (J. Phys. Chem. A 2006, 110, 38). The calculated absorption spectra of optically excited states can be used to simulate ultrafast optical pump/X-ray probe experiments.

Magnesium K-Edge NEXAFS Spectroscopy of Chlorophyll a in Solution

“…First, the experimental results were compared to previous work on calculated absorption near-edge spectra of Mg porphyrins . Second, DFT calculations of Mg NEXAFS of the correct Chl a molecule structure were computed to verify the results.…”

“…As a first approximation, porphyrins, as well as (metal-) phthalocyanines can be used as model systems for biological redox-active compounds such as Chls in PS II due to their similar molecular structure. , Comparison to other porphyrins can be justified because all transitions, which are probed in the near-edge region, are mainly located on the central tetrapyrrole ring (see Figure ) and are, therefore, comparable to the general porphyrin structure. NEXAFS spectra of magnesium- and zinc-containing porphyrins have been calculated using a time-dependent density functional theory (TDDFT) as well as a time- dependent Hartree–Fock (TDHF) approach . However, the presented results are not readily applicable to the behavior of the Mg atom in Chl because they are dealing with an ideal porphyrin structure where all MOs are highly symmetric.…”

Towards Understanding Excited-State Properties of Organic Molecules Using Time-Resolved Soft X-ray Absorption Spectroscopy

“…The extension of the pump-probe approach to very long or very short wavelengths [27] together with advanced simulation techniques [28][29][30] allow a detailed analysis of excited-state dynamics in organic molecules or biomolecular structures on a ns-to-fs time level. Optical pump soft X-ray probe spectroscopy is a relatively new approach to detect and characterize optically dark states in organic molecules [31][32][33][34] exciton dynamics [35,36] or transient ligand-to-metal charge transfer states in metalloporphyrins [37].…”

“…The simulation of the NEXAFS spectrum of an optically excited state (as for tr-NEXAFS) requires a higher effort (for porphyrin molecules cp. [29]), and it was not in the scope of this publication. However, such simulations are planned for the future.…”

Four-Component Damped Density Functional Response Theory Study of UV/Vis Absorption Spectra and Phosphorescence Parameters of Group 12 Metal-Substituted Porphyrins

“…88 Concerning more extensive basis set investigations, we refer to previous studies on UV/vis-absorption that find only modest dependencies of these linear response properties on the addition of polarization and diffuse functions. 23,28,92,93 As most standard basis sets are optimized for non-relativistic calculations, it can be expected that they perform worse for relativistic calculations where the inner core orbitals are typically contracted. For the metal atoms, we therefore employ uncontracted basis sets and the issue is only a concern for the description of the core orbitals of C and N. Performed tests of decontraction showed, however, that the use of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 In Fig.…”