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Studies of interfacial electron transfer (IET) in TiO2surfaces functionalized with (1) pyridine-4-phosphonic acid, (2) [Ru(tpy)(tpy(PO3H2))]2+, and (3) [Ru(tpy)(bpy)(H2O)−Ru(tpy)(tpy(PO3H2))]4+(tpy = 2,2′:6,2′′-terpyridine; bpy = 2,2′-bipyridine) are reported. We characterize the electronic excitations, electron injection time scales, and interfacial electron transfer (IET) mechanisms through phosphonate anchoring groups. These are promising alternatives to the classic carboxylates of conventional dye-sensitized solar cells since they bind more strongly to TiO2surfaces and form stable covalent bonds that are unaffected by humidity. Density functional theory calculations and quantum dynamics simulations of IET indicate that electron injection in 1−TiO2can be up to 1 order of magnitude faster when 1is attached to TiO2in a bidentate mode (τ ∼ 60 fs) than when attached in a monodentate motif (τ ∼ 460 fs). The IET time scale also depends strongly on the properties of the sensitizer as well as on the nature of the electronic excitation initially localized in the adsorbate molecule. We show that IET triggered by the visible light excitation of 2−TiO2takes 1−10 ps when 2is attached in a bidentate mode, a time comparable to the lifetime of the excited electronic state. IET due to visible-light photoexcitation of 3−TiO2is slower, since the resulting electronic excitation remains localized in the tpy−tpy bridge that is weakly coupled to the electronic states of the conduction band of TiO2. These results are particularly valuable to elucidate the possible origin of IET efficiency drops during photoconversion in solar cells based on Ru(II)−polypyridine complexes covalently attached to TiO2thin films with phosphonate linkers. [ABSTRACT FROM AUTHOR]

Density Functional calculations have been performed to calculate the one-electron oxidation potential for ferrocene and the redox couples for a series of small transition metal compounds of the first-, second-, and third-row elements. The solvation effects are incorporated via a self-consistent reaction field (SCRF), using the polarized continuum model (PCM). From our study of seven different density functionals combined with three different basis sets for ferrocene, we find that no density functional method can reproduce the redox trends from experiment when referencing our results to the experimentalabsolute standard hydrogen electrode (SHE) potential. In addition, including additional necessary assumptions such as solvation effects does not lead to any conclusion regarding the appropriate functional. However, we propose that if one references their transition metal compounds results to the calculatedabsolute half-cell potential of ferrocene, they can circumvent the additional assumptions necessary to predict a redox couple. Upon employing this method on several organometallic and inorganic complexes, we obtained very good correlation between calculated and experimental values (R2= 0.97), making it possible to predict trends with a high level of confidence. The hybrid functional B3LYP systematically underestimates the redox potential; however, the linear correlation between DFT and experiment is good (R2= 0.96) when including a baseline shift. This protocol is a powerful tool that allows theoretical chemists to predict the redox potential in solution of several transition metal complexes a priori and aids in the rational design of redox-active catalysts. [ABSTRACT FROM AUTHOR]

We have performed DFT and TD-DFT calculations on Pt(dcbpy)Cl2(1) and [Pt(ttpy)phenylacetylide]+(2+) to study the stability of these Pt(II) species upon reduction and photoexcitation; we found that while these compounds are stable upon reduction, photoexcitation of the reduced species leads to dissociation of the ligand set. [ABSTRACT FROM AUTHOR]