Fluorescence properties of nanoaggregates of pyrene ammonium derivative and its photoinduced dissolution and reaction in tetrahydrofuran/aqueous solutions

Abstract

We studied the fluorescence properties of nanoaggregates of pyrene ammonium derivative (PyAm) and their photoinduced dissolution and reaction in tetrahydrofuran (THF)/aqueous solution. The final concentration (dye concentration after reprecipitation) dependence of the fluorescence peak was measured. The fluorescence peak of PyAm that originated from the excimer is shifted to the long wavelength side increasing with the final concentration, which is ascribable to the characteristic fluorescence spectral changes depending on their size. The size-dependent fluorescence change in the nanoaggregates is related to some molecular conformation, packing, and elastic properties of the nanoparticles at the surface. To understand the fluorescence properties of the intermediates from aggregates to crystals is important for the studies of organic nanocrystals/aggregates prepared by the reprecipitation methods. We also determined the fluorescence spectra of the PyAm nanoaggregates in a THF/aqueous solution by photoinduced dissolution and reaction. It originated from the photochemical reaction between PyAm and THF. Changes in the perpendicular light scattering intensity by photoirradiation supports the photoinduced dissolution of PyAm in the THF/aqueous solution. These findings are important in the research field of photochemical reactions in organic nanocrystals.