Siloxanes with the general formula R-(CH2)n-Si-(OR')3 form durable bonds with inorganic materials upon hydrolysis of
labile -OR' groups, and serve as robust coupling agents between organic and inorganic materials. In the field of dye-sensitized
solar cells, functionalization of TiO2 thin-films with siloxane adsorbates has been shown to be useful as a
surface-passivation technique that hinders recombination processes and improves the overall efficiency of light-to-electricity
conversion. However, the attachment of siloxane adsorbates on TiO2 surfaces still remains poorly understood
at the molecular level. In this paper, we report the characterization of 3-(triethoxysilyl) propionitrile (TPS) adsorbates,
covalently attached onto TiO2 surfaces. We combine synthetic methods based on chemical vapor deposition, Fourier
transform (FT) infrared (IR) spectroscopy and electronic structure calculations based on density functional theory (DFT).
We predict that trifunctional siloxanes form only 2 covalent bonds, in a 'bridge' mode with adjacent Ti4+ ions on the
TiO2 surface, leaving 'dangling' alkoxy groups on the surface adsorbates. Our findings are supported by the observation
of a prominent fingerprint band at 1000-1100 cm-1, assigned to Si-O-C stretching modes, and by calculations of binding
enthalpies at the DFT B3LYP/(LACVP/6-31G**) level of theory indicating that the 'bridge' binding (ΔHb= -55 kcal
mol-1) is more stable than 'tripod' motifs (ΔHb= -45 kcal mol-1) where siloxanes form 3 covalent bonds with the TiO2
surface. The alkoxysiloxane groups are robust under heat and water treatment and are expected to be particularly
relevant for analytical methods since they could be exploited for immobilizing other functionalities onto the TiO2 surfaces.