Weakened Triplet-Triplet Annihilation of Diiodo-BODIPY Moieties without Influence on Their Intrinsic Triplet Lifetimes in Diiodo-BODIPY-Functionalized Pillar[5]arenes.

The triplet-triplet annihilation (TTA) effect of sensitizers themselves can lead to the additional quenching of lifetimes of triplet states; therefore, how to weaken the TTA effect of sensitizers is an urgent issue to be resolved for their further applications. Besides, it remains a tremendous challenge for constructing supramolecular systems of photosensitizers based on photosensitizer-functionalized pillararenes because there have been very few investigations on them. Thus, 2,6-diiodo-1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene () and ethoxy pillar[5]arene () were utilized to synthesize a -functionalized pillar[5]arene (), a cyano-containing () used as a guest molecule was also prepared, and they were used to investigate the electron-transfer mechanism between and moieties and weaken the TTA effect of moieties. The theoretical computational results of frontier molecular orbitals and isosurfaces of spin density preliminarily predicted that the cavities of the moiety had influence on the fluorescence emission of units but not on their triplet states in . The fluorescence emission intensities in a variety of solvents with different polarities and electrochemical studies revealed that there was electron transfer from to the units, and the electron-transfer process had influence on the fluorescence emission but not on the triplet states of moieties in , which verified the results of density functional theory calculations. The triplet state lifetimes of were longer than those of and and the photooxidation abilities of were better than those of and at a high concentration (1.0 × 10 M) in various solvents; in contrast, the intrinsic triplet state lifetimes and singlet oxygen quantum yields (Φ) of , , and were very similar. This was because the steric hindrance of moieties could weaken the TTA effect of moieties without influencing their intrinsic triplet state lifetimes in .