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

We report on the mechanism and efficiencies of singlet oxygen O-2((1)Delta(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)Delta(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)Delta(g)) quantum yields (Phi(Delta)) were measured by quantifying the characteristic phosphorescence of O-2((1)Delta(g)) in the NIR region (similar to 1268 nm). It was found that incorporation of relatively small amounts of PtOEP to F8BT NP results in a significant increase of Phi(Delta). NP containing 10% PtOEP (w/w) show a Phi(Delta) similar to 0.24, which is 3 times larger than that observed for undoped F8BT NP, and larger than the reported for most water-soluble porphyrins. Phi(Delta) were also calculated from the oxidation rates (v(o)) of 3-[10-(2-carboxyethyl)anthracen-9-yl]propanoic acid (ADPA), a well-known chemical O-2((1)Delta(g)) trap. Unexpectedly, this method was found to significantly overestimate the Phi(Delta) 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 similar to 8 x 10(3) M-1 and an (average) number of NP-inding sites of similar to 14000. These results necessarily caution about the use of ADPA as a probe to evaluate (DA 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. (C) 2017 Elsevier Ltd. All rights reserved.