Perylene-Derived Triplet Acceptors with Optimized Excited State Energy Levels for Triplet-Triplet Annihilation Assisted Upconversion

A series of perylene derivatives are prepared as triplet energy acceptors for triplet-triplet annihilation (TTA) assisted upconversion. The aim is to optimize the energy levels of the T-1 and S-1 states of the triplet acceptors, so that the prerequisite for TTA (2E(T1) > E-S1) can be better satisfied, and eventually to increase the upconversion efficiency. Tuning of the energy levels of the excited states of the triplet acceptors is realized either by attaching aryl groups to perylene (via single or triple carbon-carbon bonds), or by assembling a perylene-BODIPY dyad, in which the components present complementary S-1 and T-1 state energy levels. The S-1 state energy levels of the perylene derivatives are generally decreased compared to perylene. The anti-Stokes shift, TTA, and upconversion efficiencies of the new triplet acceptors are improved with respect to the perylene hallmark. For the perylene-BODIPY dyads, the fluorescence emission was substantially quenched in polar solvents. Moreover, we found that extension of the pi-conjugation of BODIPY energy donor significantly reduces the energy level of the S-1 state. Low S-1 state energy level and high T-1 state energy level are beneficial for triplet photosensitizers.