Acetylacetonate Anchors for Robust Functionalization of TiO₂Nanoparticles with Mn(II)−Terpyridine Complexes

Abstract

A novel class of derivatized acetylacetonate (acac) linkers for robust functionalization of TiO2 nanoparticles (NPs) under aqueous and oxidative conditions is reported. The resulting surface adsorbate anchors are particularly relevant to engineering photocatalytic and photovoltaic devices since they can be applied to attach a broad range of photosensitizers and photocatalytic complexes and are not affected by humidity. Acac is easily modified by CuI-mediated coupling reactions to provide a variety of scaffolds, including substituted terpy complexes (terpy = 2,2':6,2''-terpyridine), assembled with ligands coordinated to transition-metal ions. Since Mn-terpy complexes are known to be effective catalysts for oxidation chemistry, functionalization with Mn(II) is examined. This permits visible-light sensitization of TiO2 nanoparticles due to interfacial electron transfer, as evidenced by UV-vis spectroscopy of colloidal thin films and aqueous suspensions. The underlying ultrafast interfacial electron injection is complete on a subpicosecond time scale, as monitored by optical pump-terahertz probe transient measurements and computer simulations. Time-resolved measurements of the Mn(II) EPR signal at 6 K show that interfacial electron injection induces Mn(II) --> Mn(III) photooxidation, with a half-time for regeneration of the Mn(II) complex of ca. 23 s.

Theoretical studies of dye-sensitised solar cells: from electronic structure to elementary processes

“…235 DFT modelling of TiO 2 -anchoring group systems combined with extended H€ uckel Hamiltonian simulations of ET were applied to Mn(II)-terpyridyl complexes with catechol and acetylacetonate anchoring groups. 159,238 The calculated timescales for electron injection were 50-100 fs, in agreement with the experimental upper limit of $300 fs. 159,238 Sensitisers with the phosphonic acid anchoring group have also been considered by the Batista group: pyridine-4-phosphonic acid and ruthenium pyridyl complexes with the phosphonate anchoring group on anatase (101).…”

“…159,238 The calculated timescales for electron injection were 50-100 fs, in agreement with the experimental upper limit of $300 fs. 159,238 Sensitisers with the phosphonic acid anchoring group have also been considered by the Batista group: pyridine-4-phosphonic acid and ruthenium pyridyl complexes with the phosphonate anchoring group on anatase (101). 234 The calculated ET time from pyridine-4-phosphonic acid in the bidentate adsorption mode (60 fs) was faster than for the monodentate adsorption mode (460 fs), but both were significantly slower than earlier theoretical predictions made with different techniques: using the full width at half maximum (FWHM) of the dye's LUMO state as a measure of injection time (32-35 fs) 166 and using model Hamiltonian calculations (11 fs).…”

What Makes the Photocatalytic CO2 Reduction on N-Doped Ta2O5 Efficient: Insights from Nonadiabatic Molecular Dynamics

“…[24][25][26][27][28][29][30][31][32][33] Yet, there is still significant controversy in attributing observed efficiencies to particular atomic-scale mechanisms.…”

An expression for the bridge-mediated electron transfer rate in dye-sensitized solar cells

“…For this reason, the only systematic pathway towards more efficient cells is the separate optimization of the devices' individual components. This approach has been gaining momentum recently, with studies focused, for example, on the dye's anchoring group [10,11], where a computational study has been performed to predict the relative stability of the attachment and the efficiency of charge transfer across these anchors [12]. The design of new synthetic procedures for TiO 2 nanoparticles exposing different crystallographic faces [13] has added another tool for the engineering of interfacial electron transfer, with the CI process being noticeably affected by surface morphology [14][15][16].…”