Absorption mechanism of dopamine/DOPAC modified TiO 2 nanoparticles by time-dependent density functional theory calculations

TL;DR

This study uses time-dependent density functional theory to analyze how dopamine and DOPAC molecules modify TiO2 nanoparticles, revealing new absorption features and charge transfer mechanisms relevant for various photonic applications.

Contribution

It provides the first detailed theoretical insight into the absorption mechanisms of dopamine/DOPAC-modified TiO2 nanoparticles, considering nanoparticle curvature and molecular orientation effects.

Findings

Identification of direct charge transfer injection without involving lowest conduction band states

Absorption intensity increases with molecular packing and perpendicular orientation

Curvature and coverage significantly influence absorption properties

Abstract

Donor-modified TiO 2 nanoparticles are interesting hybrid systems shifting the absorption edge of this semiconductor from the ultra-violet to the visible or infrared light spectrum, which is a benefit for several applications ranging from photochemistry, photocatalysis, photovoltaics, or photodynamic therapy. Here, we investigate the absorption properties of two catechol-like molecules, i.e. dopamine and DOPAC ligands, when anchored to a spherical anatase TiO 2 nanoparticle of realistic size (2.2 nm), by means of time-dependent density functional theory calculations. By the differential absorbance spectra with the bare nanoparticle, we show how it is possible to determine the injection mechanism. Since new low-energy absorption peaks are observed, we infer a direct charge transfer injection, which, unexpectedly, does not involve the lowest energy conduction band states. We also find that the more perpendicular the molecular benzene ring is to the surface, the more intense is the absorption, which suggests aiming at high molecular packing in the synthesis. Through a comparative investigation with a flat TiO 2 surface model, we unravel both the curvature and coverage effects.