Elucidating photophysics-photochemistry relationship in singlet fission materials

Photodegradation poses a significant challenge in organic optoelectronic devices; understanding its relationship with photophysics is necessary for optimizing optoelectronic performance and photostability. We study such relationship in singlet fission (SF) materials TIPS-Pentacene (TIPS-Pn) and tetracene derivatives (R-Tc) with different morphologies. We explore how photochemistry can promote understanding of intermolecular processes such as SF through the evolution of excited states during photodegradation. Photoluminescence emission competitive to SF experiences a large increase in yield during photodegradation as SF pathways are disabled from either endoperoxide formation (in air) or photodimerization (without air) degradation processes. We observe morphology-dependent photodimerization in TIPS-Pn films and R-Tc crystals and multiple emissive states in R-Tc crystals. The ‘slip-stack’ packing motif in R-Tc crystals favors formation of emissive trap states and promotes photodimerization. In strong external magnetic fields that suppress SF in R-Tc, enhanced photodimerization is observed, which suggests that morphologies conducive to triplet pair separation could reduce photodimerization.