Enhanced Triplet-Triplet Energy Transfer and Upconversion Fluorescence through Host-Guest Complexation

Perylene-tethered pillar[5]arenes and C-60-boron-dipyrromethene (BODIPY) dyads were synthesized acting as emitters and organic triplet photosensitizers, respectively, for the purpose of improving the efficiency of triplet triplet annihilation upconversion (TTA-UC). The photophysical properties of the sensitizers (guests) and the emitters (hosts) were not greatly influenced by the chemical modifications except for a notable decrease in the fluorescence quantum yields of the perlyene emitters due to the high local concentration. The perylene-tethered pillar[5]arenes form stable 1:1 complexes with a nitrile-bearing C-60-BODIPY dyad, showing association constants as high as 4.0 x 10(4) M-1. Through host guest complexation, the efficiencies of both triplet triplet energy transfer and TTA were significantly enhanced, which overcompensated for the loss of the fluorescence quantum yield of the emitters (hosts). Thus, an improved TTA-UC efficiency of 3.2% was observed even at a diluted concentration of 6 x 10(-5) M, demonstrating for the first time the effectiveness of the supramolecular motif for enhancing TTA-UC without varying the inherent photophysical properties of sensitizers and emitters.