Quest for singlet fission of organic sulfur-containing systems in the higher lying singlet excited state: application prospects of anti-Kasha's rule

In this study, we explore the possibilities of the deactivating pathways of organic thione containing systems through first-principles calculations. We particularly pay attention to the second lying singlet excited state, S-2, due to its large energy difference from the lowest lying S-1 state in the sulfur-containing systems. Several theoretical models including the previously synthesized thiones and the strategically designed molecules are investigated to search for the basic conjugation unit that exhibits the prospect of S-2 fission. Various molecular motifs and different substituents are combined to maneuver the relative alignment of the relevant low excited energy states. The results lead us to conclude that the thione derivatives, under rational and delicate molecular designs, may be engineered to possess a sufficiently high S-2-S-1 energy gap as high as 2 eV and that these systems may exhibit S-2 fission to triplet excitons in the red to near infrared region.

Automated summary

In this study, we investigate the deactivating pathways of organic thione containing systems using first-principles calculations. We focus on the S-2 state, which has a large energy difference from the lowest lying S-1 state in sulfur-containing systems. By exploring various theoretical models and molecular designs, we find that thione derivatives can be engineered to possess a high S-2-S-1 energy gap as high as 2 eV, leading to S-2 fission to triplet excitons in the red to near infrared region.