9,10-Di(hydroxymethylphenyl)anthracenes: Highly efficient triplet annihilators with small singlet-triplet energy gap (ΔEST) and planar configuration

Abstract A series of 9,10-di(hydroxymethylphenyl) anthracene chromophores (named as E-o-DHMPA, Z-o-DHMPA, m-DHMPA and p-DHMPA) are designed to tailor triplet-triplet annihilation upconversion through isomer engineering. It was found that improving molecular planarity makes for molecular π-π interaction, meanwhile, molecular excited singlet energy level (ES1) shows decreasing; however, the triple energy level (ET1) exhibits almost equal. Thus, small singlet-triplet energy gap (ΔEST) of chromophores could be designed. Selective excitation of sensitizer (palladiumIItetrabromophenylporphyrin, PdBrTPP) in solution containing annihilator results in the UC efficiency (ΦUC) increasing from E-o-DHMPA (15.9%), Z-o-DHMPA (18.7%), m-DHMPA (26.0%) to p-DHMPA (26.8%), accompanied by the excitation threshold intensity (Ith, mW⋅cm−2) decreasing from E-o-DHMPA (292.74), Z-o-DHMPA (174.41), m-DHMPA (36.58) to p-DHMPA (29.78), which are in agreement with the ΔEST decreasing and planarity improving of these isomers. Annihilator with small energy gap (ΔEST) and planar configurtion has contribution to triplet-triplet annihilation (TTA), supported by the fact of the Ith value reducing, and thereby increasing UC efficiency (ΦUC), which provides a new strategy for molecule design to develop new triplet annihilator. Finally, the TTA-UC powered photolysis of bilirubin was conducted for the first time, suggesting that TTA-UC can act as an effective light source used in the light therapy for neonatal hyperbilirubinemia.