Theoretical Study of Singlet Fission in Oligorylenes.

Using the time-dependent tuned long-range corrected density functional theory method, the feasibility for singlet fission in oligorylenes has been investigated within the scope of the diradical character based guideline and of the energy level matching conditions for the isolated monomers. It is found that the relatively small-size oligorylenes, that is, terrylene and quaterrylene, which present intermediate diradical character without significant tetraradical character, are possible candidates for energetically efficient singlet fission. In relation to this result, we also raise the possibility that the unsettled ultrafast dynamics previously observed on quaterrylene is evidence for singlet fission.