Nanoparticle formation of pentacene by laser irradiation in ethanol solution

Laser irradiation using a Nd3+:YAG laser (532nm, 8ns, 10Hz) on an ethanol suspension of micrometer-sized pentacene crystals induced absorption spectral changes in the solution, as a result of the formation of pentacene nanoparticles. The nanoparticles were platelike crystals. The nanoparticles formed by irradiation with a fluence of 50 mJ/cm(2) for 3.0 min were 4-13 nm in height and 10-70 nm in width. The threshold laser fluence for the formation was determined to be ca. 20 mJ/cm(2), and irradiation with fluences above 80 mJ/cm(2) induced the decomposition of the pentacene nanoparticles. The nanoparticle size decreased with an increase in the laser fluence,which was reflected in the longest-wavelength peak position of the absorption bands of the pentacene nanoparticles. On the basis of these results, the mechanism of pentacene nanoparticle formation by laser irradiation is discussed in connection with those of vanadyl phthalocyanine and quinacridone systems reported by Masuhara and coworkers [J. Phys. Chem. A 106 (2002) 2135; Jpn. J. Appl. Phys. 42 (2003) 2725; Jpn. J. Appl. Phys. 45 (20061) 384].