Amplified singlet oxygen generation in metallated-porphyrin doped conjugated polymer nanoparticles

• Autores: Spada, Ramiro Martín; Macor, Lorena Paola; Hernández, Laura; Ponzio, Rodrigo Andrés; Ibarra, Luis; Lorente, Carolina; Chesta, Carlos A.; Palacios, Rodrigo Emiliano
• Año de publicación: 2018
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas; Química; Conjugated polymer nanoparticles; Metallated porphyrin; Photosensitization; Singlet oxygen quantum yield; Dye adsorption
• Institución: Universidad Nacional de La Plata

Abstract We report on the mechanism and efficiencies of singlet oxygen O₂(¹Δ_g) generation of nanoparticles (NP) of the conjugated polymer (CP) poly(9,9-dioctylfluorene- alt -benzothiadiazole) (F8BT) doped with platinum octaethylporphyrin (PtOEP) suspended in water. A detailed study of the photophysics of these NP, using stationary and time-resolved absorption and emission techniques, indicates that O₂(¹Δ_g) is generated by the triplet excited state of F8BT and not by that of PtOEP, as previously observed for other porphyrin doped CP NP. O₂ (¹Δ_g) quantum yields (Φ_Δ) were measured by quantifying the characteristic phosphorescence of O₂(¹Δ_g) in the NIR region (∼1268 nm). It was found that incorporation of relatively small amounts of PtOEP to F8BT NP results in a significant increase of Φ_Δ. NP containing 10% PtOEP (w/w) show a Φ_Δ ∼ 0.24, which is 3 times larger than that observed for undoped F8BT NP, and larger than the reported for most water-soluble porphyrins. Φ_Δ were also calculated from the oxidation rates ( v 0 ) of 3-[10-(2-carboxyethyl)anthracen-9-yl]propanoic acid (ADPA), a well-known chemical O₂(¹Δ_g) trap. Unexpectedly, this method was found to significantly overestimate the Φ_Δ values due to the adsorption of ADPA on the surface of NP. The ADPA/NP adsorption process was characterized using a simple adsorption model yielding an (average) equilibrium constant of ∼8 × 10³ M⁻¹ and an (average) number of NP-binding sites of ∼14000. These results necessarily caution about the use of ADPA as a probe to evaluate Φ_Δ in these NP systems. In addition, the interaction of F8BT NP with other anionic, cationic and zwitterionic dyes (dissolved in water) was studied. It was found that even at nano-molar concentrations all the dyes efficiently adsorb on the NP surface. This general and simple self-assembly strategy can be used to prepare superficially-dye-doped CP NP with potentially interesting technological applications.
Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas