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

• DOI: 10.1016/j.dyepig.2017.09.044
• Publication Date: 2017-09-20T16:31:28Z
• Authors: Ramiro M. Spada; Lorena P. Macor; Laura I. Hernández; Rodrigo A. Ponzio; Luis E. Ibarra; Carolina Lorente; Carlos A. Chesta; Rodrigo E. Palacios
• Keywords: Propanoic acid

Abstract We report on the mechanism and efficiencies of singlet oxygen O 2 ( 1 Δ 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 O 2 ( 1 Δ 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. O 2 ( 1 Δ g ) quantum yields (Φ Δ ) were measured by quantifying the characteristic phosphorescence of O 2 ( 1 Δ 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 O 2 ( 1 Δ 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 × 10 3 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.