Preparation of nanoparticles of a violanthrone derivative with properties of J-like aggregates

Abstract

Organic nanoparticles of violanthrone 78, a violanthrone derivative, were prepared by a reprecipitation method. The nanoparticles were annealed at 60°C and the nanoparticles were changed to J-aggregates. UV/visible spectra, fluorescence spectra, and fluorescence lifetimes of the nanoparticles prepared were measured. UV/visible spectra shows that the wavelength of main absorption band shifted from 610 nm to 630 nm after annealing, and the absorbance of the band increased by more than twice, and sharpening of the main band was also observed. Nanoparticles without annealing were not fluorescent. After annealing, fluorescence of the nanoparticles with a small Stokes shift was observed at 650 nm. From these results, it was suggested that the J-aggregates phase transition occurred by annealing. Fluorescence lifetime of the annealed nanoparticles was as short as 20 ps.