Triplet Formation and Triplet-Triplet Annihilation Upconversion in Iodine Substituted Non-Orthogonal BODIPY-Perylene Dyads

BODIPY-perylene dyads have emerged as useful metal free sensitizers for triplet-triplet annihilation upconversion (TTAUC), these dyads are capable of efficient triplet generation via spin-orbit charge transfer intersystem crossing (SOCT-ISC). This important route to triplet formation requires dyads in which two moieties are oriented perpendicular to each other. In this contribution, we give a deeper insight on the behaviour of established BODIPY-perylene dyads, where BODIPY-perylene dihedral exhibits non-orthogonal dyad geometry. The intersystem crossing of BODIPY-perylene dyads with and without iodine are investigated using femtosecond transient absorption (fs-TA) and nanosecond transient absorption (ns-TA) spectroscopy. The concurrent decay of the singlet charge transfer state (1CT) and rise of triplet states in both the iodinated and non-iodinated dyads confirms the SOCT-ISC as the main intersystem crossing pathway despite the altered geometry of the dyads. The presence of an iodine atom on the BODIPY-moiety enables intersystem crossing 2.6-times faster and provides a higher triplet yield with respect to dyad without iodine. The upconversion quantum yield (𝜙𝜙S UC) is 8.4-times higher in the sample containing iodinated dyad as sensitizer and perylene as annihilator. The triplet-triplet energy transfer rate (kTTET) is ~8x108 M-1 cm-1 for both iodinated and non-iodinated sensitizer containing TTAUC systems in 1,4-dioxane.