Formation of 3,4,9,10-perylenetetracarboxylicdianhydride nanoparticles with perylene and polyyne byproducts by 355 nm nanosecond pulsed laser ablation of microcrystal suspensions

Nanoparticles of the insoluble organic compound 3,4,9,10-perylenetetracarboxylicdianhydride were prepared by nanosecond pulsed laser irradiation of microcrystalline solid suspensions in polar solvents using the 3rd harmonic (355 nm) from a Nd:YAG laser. The initially cloudy suspensions became transparent clear red dispersions that passed through a 0.2 μm membrane filter 1 day after 30 min of irradiation at laser fluences greater than 130 mJ cm^-2. Filtering reduced the red color indicating that it originated from light absorption by particles or aggregates with a size range spanning the 0.2 μm filter cut-off. This is consistent with scanning electron microscope images. Whether or not the particles passed through the filter depended on how long they were aged. Initially formed dispersions did not pass through, whereas those which had been aged for several hours did, indicating that the nanoparticles were aggregated and that the aggregate size depended on the standing time after laser irradiation. HPLC analysis revealed perylene and C₈, C₁₀, C₁₂, C₁₄ polyynes byproducts, which probably formed respectively in a 3 photon photochemical and a photothermal processes at the surface of the PTCDA particles. Initially the perylene production rate was rapid, but as the PTCDA particles' surface became decomposed it slowed down. However, it increased again as the surface area of the PTCDA particles became larger as smaller nanoparticles formed and after the thermal decomposition of the surface was quenched. When the particles became smaller the thermal processes were quenched and polyyne production stopped.