Bound excitons and many-body effects in x-ray absorption spectra of azobenzene-functionalized self-assembled monolayers

TL;DR

This study uses advanced computational methods to analyze x-ray absorption spectra of azobenzene-functionalized SAMs, revealing strong, exciton-driven core-edge excitations with significant binding energies.

Contribution

It provides new insights into excitonic effects and the character of near-edge resonances in azobenzene SAMs using the Bethe-Salpeter equation approach.

Findings

Core-edge excitations are intense and strongly bound.

Binding energies range from 6 to 4 eV depending on molecular packing.

Electron-hole correlation dominates the excitations, exchange interaction is negligible.

Abstract

We study x-ray absorption spectra of azobenzene-functionalized self-assembled monolayers (SAMs), investigating excitations from the nitrogen K edge. Azobenzene with H-termination and functionalized with CF3 groups is considered. The Bethe-Salpeter equation is employed to compute the spectra, including excitonic effects, and to determine the character of the near-edge resonances. Our results indicate that core-edge excitations are intense and strongly bound: Their binding energies range from about 6 to 4 eV, going from isolated molecules to densely-packed SAMs. Electron-hole correlation rules these excitations, while the exchange interaction plays a negligible role.