Luminescence enhancement of organic nanoparticles induced by photocrosslinking

Driving the interactions between organic nanoparticles and phospolipidic membranes by an easy treatment of the surface stabilizer

Polymer-stabilized perylene nanoparticles were prepared through a solvent exchange method. The formation of the nanostructures in aqueous solution was confirmed by the appearance of a red-shifted emission attributable to the formation of excimer-like aggregates. The behavior of organic nanostructures in the presence of lipid vesicles was investigated through steady-state and time-resolved fluorescence measurements. When no further surface treatment is applied to the nanoparticles, changes in the decay times and emission spectra demonstrate that inside the lipid bilayers the nanoparticles redissolve into the monomeric form with a rate and efficiency determined by the working temperature (above and below the transition temperature Tm of the phospholipid). On the other hand, when the stabilized shell is UV-cured to induce photo-cross-linking of the polymeric chains, the nanoparticle stability increases and their redissolution in the membrane is prevented. Confocal fluorescence images support the data obtained in bulk. The results indicate that the prepared nanostructures could be successfully used either as nanometric carriers for the delivery of poor water-soluble lipophilic compounds or as imaging tools depending on the rigidity/cross-linking degree of their polymeric stabilizer shell.

Tuning photoluminescence of organic rubrene nanoparticles through a hydrothermal process

Light-emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) nanoparticles (NPs) prepared by a reprecipitation method were treated hydrothermally. The diameters of hydrothermally treated rubrene NPs were changed from 100 nm to 2 μm, depending on hydrothermal temperature. Photoluminescence (PL) characteristics of rubrene NPs varied with hydrothermal temperatures. Luminescence of pristine rubrene NPs was yellow-orange, and it changed to blue as the hydrothermal temperature increased to 180°C. The light-emitting color distribution of the NPs was confirmed using confocal laser spectrum microscope. As the hydrothermal temperature increased from 110°C to 160°C, the blue light emission at 464 to approximately 516 nm from filtered-down NPs was enhanced by H-type aggregation. Filtered-up rubrene NPs treated at 170°C and 180°C exhibited blue luminescence due to the decrease of intermolecular excimer densities with the rapid increase in size. Variations in PL of hydrothermally treated rubrene NPs resulted from different size distributions of the NPs.