Uncover the Mechanism of Amplified Triplet‐Triplet Annihilation Upconversion in a Chiral Photonic System

ABSTRACT Triplet‐triplet annihilation upconversion (TTA‐UC) in aggregate systems with high efficiencies has enormous potential for extensive application scenarios. However, it is still plagued with problems of not only toxicity and encapsulation difficulties resulting from organic solvents but low efficiencies in aggregate systems. Here, we construct a novel TTA‐UC aggregate system featured with a chiral photonic medium by directly doping a TTA‐UC dye pair into a cholesteric liquid crystal host with a specific photonic stopband. The upconversion emission was raised to the most accompanying with a decreased threshold when the photonic stopband inhibits the phosphorescence of the sensitizer leading to a promoted triplet‐triplet energy transfer process. This work uncovers a novel mechanism to construct TTA‐UC‐featured aggregate systems with boosted upconversion efficiencies, which demonstrates potentials for practical applications including photovoltaics and chiroptics.