Unusual photoluminescence characteristics of tetraphenylpyrene (TPPy) in various aggregated morphologies

We found that 1,3,6,8-tetraphenylpyrene (TPPy) demonstrates unusual photoluminescence (PL) characteristics in the solid-state morphologies. We investigated the PL characteristics of TPPy in various morphologies including powder, deposited film, and solutions. The TPPy powder (A), which was prepared through column chromatography, recrystallization, and train sublimation, showed blue fluorescence with a peak of maximum wavelength of λmax = 451 nm. The TPPy powder (B), which was obtained by thermal annealing of TPPy powder (A) in a quartz tube in nitrogen, showed green fluorescence with λmax = 510 nm. Furthermore, the TPPy powder (B) was reversibly converted into TPPy powder (A) by recrystallization. We conclude that TPPy dimers form locally in the TPPy monomer aggregates during thermal annealing and redissociate into the monomer states during recrystallization.