Carbon and Nitrogen K-Edge NEXAFS Spectra of Indole, 2,3-Dihydro-7-azaindole, and 3-Formylindole

Abstract

The near-edge X-ray absorption fine structure (NEXAFS) spectra of indole, 2,3-dihydro-7-azaindole, and 3-formylindole in the gas phase have been measured at the carbon and nitrogen K-edges. The spectral features have been interpreted based on density functional theory (DFT) calculations within the transition potential (TP) scheme, which is accurate enough for a general description of the measured C 1s NEXAFS spectra as well as for the assignment of the most relevant features. For the nitrogen K-edge, the agreement between experimental data and theoretical spectra calculated with TP-DFT was not quite satisfactory. This discrepancy was mainly attributed to the many-body effects associated with the excitation of the core electron, which are better described using the time-dependent density functional theory (TDDFT) with the range-separated hybrid functional CAM-B3LYP. An assignment of the measured N 1s NEXAFS spectral features has been proposed together with a complete description of the observed resonances. Intense transitions from core levels to unoccupied antibonding π* states as well as several transitions with mixed-valence/Rydberg or pure Rydberg character have been observed in the C and N K-edge spectra of all investigated indoles.

Two-Dimensional Self-Assembly Driven by Intermolecular Hydrogen Bonding in Benzodi-7-azaindole Molecules on Au(111)

“…The p-polarized N K-edge spectrum (Figure a) presents the most intense peak at 398.95 eV (peak A), which can be associated with a N 1s → π* transition, localized solely on the pyridinic nitrogen (CN-C), in full agreement with gas-phase measurements on pyridine and azaindole . From comparison with the literature on pyrrole, azaindole, and imidazole, we may associate the broad and asymmetric resonance peak at 402.05 eV (peak C) with the lowest energy contribution from the pyrrolic nitrogen atom, corresponding to a N 1s → π* (N–H) transition. The assignment of the small absorption feature at 400.36 eV (peak B) is less straightforward.…”

Probing Intermolecular H-Bonding Interactions in Cyanuric Acid Networks: Quenching of the N K-Edge Sigma Resonances

“…The analysis of the TDDFT eigenvectors highlights that CAM-B3LYP yields a stronger coupling among (1h1p) core excitations compared to B3LYP, furthermore it describes more appropriately the several σ* valence–Rydberg transitions that contribute to the N 1s spectrum. This is consistent with the capability of the range-separated functionals, such as CAM-B3LYP, to better describe the Rydberg excitations compared to the B3LYP functional. , The present results therefore prove the effectiveness of the TDDFT/CAM-B3LYP computational scheme in describing the N 1s core excitations confirming what emerged in a previous theoretical investigation on the N 1s NEXAFS spectra of indole and its derivatives …”

“…59,60 The present results therefore prove the effectiveness of the TDDFT/CAM-B3LYP computational scheme in describing the N 1s core excitations confirming what emerged in a previous theoretical investigation on the N 1s NEXAFS spectra of indole and its derivatives. 61 It is important to point out that the nature of the main transitions contributing to the N 1s spectrum does not change in passing from the DFT-TP to the TDDFT approach, as can be deduced by a careful analysis of the results reported in Tables S2 and S3 of the Supporting Information. This is an important issue taking into account that the strong configuration mixing of TDDFT/CAM-B3LYP results, which provide the best description of the N 1s spectrum, makes more complex the assignment of the experimental features, and it is therefore useful to take advantage of the DFT-TP results which provide a key for the interpretation of the spectrum in terms of single particle description.…”

“… 59 , 60 The present results therefore prove the effectiveness of the TDDFT/CAM-B3LYP computational scheme in describing the N 1s core excitations confirming what emerged in a previous theoretical investigation on the N 1s NEXAFS spectra of indole and its derivatives. 61 …”

Superatomic Rydberg State Excitation

“…TD-DFT is an effective method to study excited states in complex systems. Currently, TD-DFT is widely used to describe of Rydberg states 5,. Overall full UV-vis absorption spectra of Au n (…”