Advances in Singlet Fission Chromophore Design Enabled by Vibrational Spectroscopies

Singlet fission leads to the formation of two separate triplet T₁excitons from an initial singlet S₁exciton through ¹(TT) and ¹(T...T), multiexcitonic intermediates that retain singlet character. Its ability to achieve external quantum efficiencies higher than 100% made it an attractive candidate for optoelectronic device applications. However, singlet fission has not been applied widely despite having been investigated by a myriad of spectroscopic methods, in part due to our poor understanding of how to optimize molecular structure and packing in chromophores well-suited to large-scale production. Vibrational spectroscopies provide a solution, because they directly probe nuclear motions, allowing us to monitor evolving structural changes in molecules undergoing singlet fission, thus providing us with roadmaps to design molecules suitable for optoelectronic applications. This Perspective reviews the contributions and analyzes the future directions of vibrational spectroscopies to the advancement in our knowledge about the mechanisms and rational designing of chromophores undergoing efficient singlet fission.