Critical Sensitizer Quality Attributes for Efficient Triplet–Triplet Annihilation Upconversion with Low Power Density Thresholds

Triplet-triplet annihilation upconversion (TTAUC) is a power density-dependent process where photons of low energy are transformed into high energy ones. The most important attributes of efficient TTAUC are quantum yield ΦTTAUC, power density threshold Ith (photon flux at which 50% of ΦTTAUC is achieved) and the upconversion shift of emitted photons (anti-Stokes shift). Up to date, approaches to balance these parameters have remained unclear. Herein, the cumulative effect of sensitizer triplet lifetime (τ0S), sensitizer-annihilator triplet energy gap (ΔET), and the total con-centration of the sensitizer on the power density threshold at high TTAUC quantum yields is evaluated experimentally using Pt, Pd, and Zn tetraphenylporphyrin derivatives and a tetra-tert-butylperylene annihilator, and by kinetic rate modelling. The results suggest that a large energy gap (ΔET ≥ 4 kBT) and long sensitizer triplet lifetime makes the tri-plet-triplet energy transfer (TTET) extremely efficient and allow the utilization o...