Lots of recent investigations of singlet fission have focused on crystalline polyacenes, which happen to be acknowledged for a while to undergo singlet fission. While these supplies have guarantee, limitations in stability, value, and overall performance could hinder practical application of polyacene solar Paclitaxel CAS cells, though their complicated photophysics may well restrict our basic comprehending of singlet fission in crystalline polyacenes.
On this Account, we describe rationally intended singlet fission chromophores whose excited state dynamics must be relatively very simple and whose coupling is often very well managed through the formation of covalent dimers, aggregates, or polycrystalline movies. In principle, investigations of these chromophores ought to deliver the dearest connection to theoretical ideas explaining how an excited state evolves from a singlet (Si) into two triplets (IT).
Realizing the guarantee of productive singlet fission rests with two duties: (i) producing an excellent molecular vitality degree construction and (ii) inducing the correct kind and power of chromophore coupling. In this Account, we supply theoretical guidance for attaining 0) and take into consideration more extensively latest effects aimed at (ii).
For (i), theoretical advice suggests that, in addition to alternant hydrocarbons like tetracene and pentacene, biradicals (i.e., molecules with two independent radical centers) may additionally be employed as the basis for designing chromophores with low-lying triplet states such that the power romance 2E(T-1) <= E(S-1) is satisfied.
Although molecules that do not fulfill this condition can also exhibit singlet fission from a higher lying or vibrationally energized singlet state, fast relaxation processes will likely reduce the singlet fission yield and complicate determination of the singlet fission mechanism.
For (ii), once an appropriate chromophore has been chosen, the task of coupling two or much more of them together must be done carefully. We discuss three pathways by which a dimer could undergo singlet fission: (1) A direct route in which slipped cofacial stacking is favorable under certain conditions. Cofacial stacking is common in molecular crystals, and it is likely not a coincidence that current reports of productive singlet fission involve slipped-stacked molecules in polycrystalline thin movies. (2) A mediated route in which SI interacts with (TT) via a virtual radical cation/anion state, which could be important in some situations.
(3) A two-step route (i.e., through a real charge transfer intermediate) which others have suggested theoretically. We present data on 1,3-diphenylisobenzofuran (DPIBF) dimers that are consistent with this pathway.
Finally, we review potential solar photoconversion efficiency gains utilizing singlet fission in several contexts.