Morphology-dependent singlet fission and photodegradation in functionalized tetracenes

Singlet fission (SF) is a charge carrier multiplication process that can occur in organic semiconductors and has potential to enhance (opto)electronic device performance. We examine how SF depends on molecular packing with functionalized tetracene (R-Tc) crystals which have the same monomer properties but different crystal packings with ‘slip-stack’ (R=TES) and ‘gamma’ (R=TBDMS) packing structures. Using temperature-dependent photoluminescence spectroscopy, we find that the triplet pair state (TT) in R-Tc systems under study is non-emissive, and the PL is dominated by that from low-energy emissive trap states in TES-Tc and from aggregate states in TBDMS-Tc, with the emissive channels competing with SF. We also study the effects of photodegradation from endoperoxide formation on R-Tc and the relationship between photodegradation and SF and find that the ‘gamma’-packed TBDMS-Tc is more photostable than the ‘slip-stacked’ TES-Tc derivative. To analyze SF and competitive pathways, we constructed a 4-state kinetic model to reproduce the observed PL data, which predicts maximum SF free triplet yields of 190% for TES-Tc and 185% for TBDMS-Tc at room temperature.