Local electronic properties at organic–metal interfaces: thiophene derivatives on Pt(111)

Abstract

The valence electronic states of thiophene (TP), 2-thiophenethiol (TT), 2,2'-bithiophene (BTP), and 2,2'-bithiophene-5-thiol (BTT) on Pt(111) were measured by ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy (MAES) to elucidate how the local electronic properties at the organic-metal interface are altered by the extent of π-conjugation and substituent effects. First-principles calculations using density functional theory (DFT) were used to assign the observed spectra. TP and BTP chemisorb weakly on Pt(111), whereas TT and BTT are strongly bound to Pt(111) through the S atom with the cleavage of the S-H bond, forming a thiolate. In the MAES spectra, weak emission just below the Fermi level (E(F)) was attributed to a chemisorption-induced gap state (CIGS) produced by orbital mixing between the organic species and Pt(111). The formation of CIGS is responsible for a metallic structure at the organic-metal interface. The relative intensities of CIGSs at E(F) were in the order of TP (flat-lying configuration) > TT > TP (inclined configuration), indicating that the spatial distribution of CIGSs is drastically altered by the strength of the organic-metal bond and the adsorption geometry. In other words, TP (flat-lying geometry) and TT serve as good mediators of the extension of the metal wave function at E(F), which would be closely related to charge transport at organic-metal interfaces.

Metal–Sulfur Linkages Achieved by Organic Tethering of Ruthenium Nanocrystals for Enhanced Electrochemical Nitrogen Reduction

“…After modification, there is a clear decrease in the intensity of Ru peaks that validates the surface coverage with thiols and is more prominent with long‐tail thiols (Supporting Information, Figure S7). Moreover, a peak shift of 0.1 to 0.3 eV to higher binding energy for Ru is also observed in modified samples that could be ascribed to the Ru−S thiolate bond with localized charge density sites [20] . Such localized charge density sites can potentially act as the adsorption sites for the N 2 .…”

“…Inspired by nitrogenase, here we show a Ru‐based catalyst with Ru−S linkages for NRR, achieved by facile surface modification of Ru with aliphatic thiols. Thiols are known to form self‐assembled monolayers (SAM) on Ru surfaces [20, 21] . The organic and hydrophobic nature of the SAM limits proton transfer while allowing N 2 transport to the surface of the catalyst.…”

“…Thiols are known to form self-assembled monolayers (SAM) on Ru surfaces. [20,21] The organic and hydrophobic nature of the SAM limits proton transfer while allowing N 2 transport to the surface of the catalyst. Importantly, the formation of Ru À S linkage also modifies the electronic structure to facilitate the N 2 adsorption, activation, and polarization on the active site (Ru).…”

“…Moreover, a peak shift of 0.1 to 0.3 eV to higher binding energy for Ru is also observed in modified samples that could be ascribed to the Ru À S thiolate bond with localized charge density sites. [20] Such localized charge density sites can potentially act as the adsorption sites for the N 2 . Moreover, corresponding C1s peaks are present in all samples that can be attributed to the chemical structure of rGO.…”

Local electronic structure at organic–metal interface studied by UPS, MAES, and first-principles calculation

“…Furthermore, a wave function exposed outside the surface gives more effective overlap than that localized on the surface, yielding a stronger band in the spectrum. This unique feature enables us to probe the spatial electron distribution of the surface, and therefore has been applied to directly detect gap states near E F (e.g., CIGSs for benzene on Pd(1 1 0) [11] and Pt(1 1 1) [12], dichloroethane on Pt(1 1 1) [13], alkanethiols on Pt(1 1 1) [14,15], benzenethiol and benzeneselenol on Pt(1 1 1) and Au(1 1 1) [16,17], C 60 on Pt(1 1 1) [18], thiophene derivatives on Pt(1 1 1) [19] and CBGSs for bathocuproine on K-precovered Au [20], and K-doped dibenzopentacene (DBP) [21]) and to trace the electronic response of the final hole produced at the topmost condensed layer [12,[22][23][24].…”