Absorption, luminescence, and sizing of organic dye nanoparticles and of patterns formed upon dewetting.

Organic nanoparticles made of a push-pull triarylamine dye with an average diameter of 60 nm, were prepared by reprecipitation. We study their photophysical properties by a combination of photothermal and fluorescence microscopy. Photothermal contrast provides a quantitative measure of the number of absorbers. The size of nanoparticles estimated from the absorption measurements was compared with sizes measured by AFM. Fluorescence and absorption microscopy provide quantum yield on the single-particle level as a function of excitation intensity. The quantum yield strongly decreases at high intensities because of singlet-singlet or singlet-triplet annihilation. We also report the formation of molecular thin layers and of labyrinth-shaped structures on glass substrates, presumably induced by dewetting.