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In the field of nanomedicine, significant attention is directed toward near-infrared (NIR) light-responsive inorganic nanosystems, primarily for their applications in photodynamic therapy and fluorescence bioimaging. The crucial role of the NIR range lies in enabling optimal tissue penetration, which is essential for both irradiating and detecting nanoparticles deep within the human body. In this study, we employed density functional theory (DFT) and time-dependent DFT (TDDFT) calculations to explore the structural and electronic properties of cyanine-functionalized TiO2 spherical nanoparticles (NPs) with a realistic diameter of 2.2 nm. We revealed that different adsorption configurations of cyanine (VG20-C1) on the TiO2 NP surface exhibit distinct features in the optical spectra. These cyanine dyes, serving as bifunctional linkers with two carboxylic end groups, can adsorb in either a side-on mode (binding with both end groups) or an end-on mode (binding only one end group). In end-on adsorption structures, low-energy excitations are exclusive to dye-to-dye electronic transitions, while side-on structures exhibit electron charge transfer excitations from the dye to the TiO2 NP at low energy. This thorough analysis provides a rational foundation for designing cyanine-functionalized TiO2 nanosystems with optimal optical characteristics tailored for specific nanomedical applications such as photodynamic therapy or fluorescence bioimaging.

Heterogeneous catalysis is an essential aspect for actual industrialization of chemical processes. Here a TiO2-based powder, typically used in photocatalysis, is exploited for the first time for visible-light-regulated Photoinduced Electron/Energy (PET)-reversible addition–fragmentation chain-transfer (RAFT). Titania is a non-toxic, low-cost, and heterogeneous catalyst that can offer several advantages in terms of sustainable polymerization and photocatalyst (PC) recovery. In this work, we aim not only at unraveling the mechanism of photopolymerization and the important interactions involved, but also at red-shifting the absorption region to achieve vis-light polymerization. The combination of the experimental investigation with Density Functional Theory (DFT) calculations provides new insights into the interactions between the chain transfer agents (CTAs) and the TiO2 surface, unveiling their pivotal role on the reaction rate and polymerization control. Moreover, to shift the polymerization under the less energetic blue light, high-surface area N-doped TiO2 nanoparticles are employed, avoiding the CTA degradation often observed with UV irradiation and increasing the overall sustainability of the process.

Functionalized titanium dioxide (TiO2) nanoparticles (NPs) with intense fluorescent dyes are a promising tool for several technological applications ranging from photochemistry, photocatalysis, photovoltaics, photodynamic therapy, or bioimaging. Here, we present the case study of Alizarin adsorption on TiO2 NPs of different shapes and increasing size up to 2.2 nm (700 atoms), by means of density functional theory calculations. We find that Alizarin can bind in three different ways, depending on the number and the type of bonds between Alizarin and TiO2: ‘tridented’, ‘bidented’, and ‘chelated’. Next, we investigate the optical properties of these systems by time-dependent density functional theory calculations. Based on the absorption spectra and the Kohn–Sham orbitals analysis, we discovered that the mechanism of electron injection depends on the Alizarin binding mode to the TiO2 surface. While for bidented and chelated adsorption modes, a direct charge transfer is observed; for the tridented one, an indirect mechanism governs the charge transfer process following the excitation. Our results are in good agreement with existing experimental data and suggest that by tailoring the shape of the TiO2 NPs and, thus, determining the type of undercoordinated Ti atoms prevalently exposed at the surface, it is possible to control the predominant injection mechanism.