Properties and evolution of emission in molecular aggregates of a perylene ammonium derivative in polymer matrices

Size-dependent fluorescent properties of aggregates of a perylene ammonium derivative (PeryAm) were studied by steady-state and time-resolved spectroscopic methods. Quantitative analyses of aggregated states in aqueous solution indicated that the aggregation proceeded through dimer units of PeryAm. The fluorescence of the aggregate in the PVA film prepared from the aqueous solution continuously redshifted with an increase in the concentration of PeryAm in the mother liquor while keeping the absorption spectra in almost the same band shapes. Fluorescence anisotropy values of aggregates in the PVA film were dependent on the monitoring wavelength, and time profiles of the fluorescence at longer wavelengths showed a rapid increase just after the pulsed excitation. These results indicated efficient energy transfer to the stable sites in aggregates. Fluorescence microscopy images showed that aggregates were segregated in the PVA film and the color of the emission was dependent on the size of the aggregate. Under the steady-state irradiation, the emission color of the aggregates changed from green to yellow, which was attributable to the association of a small cluster of PeryAm with the green emission resulting in the formation of yellow-colored aggregates. On the basis of these results, we have discussed the mechanisms and dynamics of the aggregation and size-dependent emission in aggregates.