RESUMO
The photophysical processes of singlet fission and triplet fusion have numerous emerging applications. They involve the separation of a photo-generated singlet exciton into two dark triplet excitons and the fusion of two dark triplet excitons into an emissive singlet exciton, respectively. The role of the excimer state and the nature of the triplet-pair state in these processes have been a matter of contention. Here we analyse the room temperature time-resolved emission of a neat liquid singlet fission chromophore and show that it exhibits three spectral components: two that correspond to the bright singlet and excimer states and a third component that becomes more prominent during triplet fusion. This spectrum is enhanced by magnetic fields, confirming its origins in the recombination of weakly coupled triplet pairs. It is thus attributed to a strongly coupled triplet pair state. These observations unite the view that there is an emissive intermediate in singlet fission and triplet fusion, distinct from the broad, unstructured excimer emission.
RESUMO
Singlet fission is an exciton multiplication process that allows for the conversion of one singlet exciton into two triplet excitons. Organic semiconductors, such as acenes and their soluble bis(triisopropylsilylethynyl) (TIPS) substituted counterparts, have played a major role in elucidating the understanding of the underlying mechanisms of singlet fission. Despite this, one prominent member of the acene family that has received little experimental attention to date is TIPS-anthracene, even with computational studies suggesting potential high singlet fission yields in the solid state. Here, time-resolved spectroscopic and magneto-photoluminescence measurements were performed on spin-cast films of TIPS-anthracene, showing evidence for singlet fission. A singlet fission yield of 19% (out of 200%) is estimated from transient absorption spectroscopy. Kinetic modeling of the magnetic field effect on photoluminescence suggests that fast rates of triplet dissociation lead to a low magnetic photoluminescence effect and that non-radiative decay of both the S1 and 1(TT) states is the cause for the low triplet yield.