Singlet fission

The phenomenon has been observed in molecular crystals, aggregates, disordered thin films, and covalently-linked dimers, where the chromophores are oriented such that the electronic coupling between singlet and the double triplet states is large.

[3] Early studies on the effect of the magnetic field on the fluorescence of crystalline tetracene solidified understanding of singlet fission in polyacenes.

Typically, the mechanisms for singlet fission are classified into (a) Direct coupling between the molecules and (b) Step-wise one-electron processes involving the charge-transfer states.

[7][8][9] It has been proposed that computational modeling of the diradical character of molecules may serve as a guiding principle for the discovery of new classes of singlet fission chromophores.

In polycrystalline films, excitons can diffuse to defect-rich regions, creating “hotspots” that enhance singlet fission, with excimer-like emissions reflecting the influence of structural defects on SF rates.

[16] When materials do not meet the energetic requirements for singlet fission, other relaxation pathways occur such as fluorescence, non-radiative decay, or intersystem crossing to a single triplet state dominate, leading to lower efficiency in photovoltaic applications.