dr. Artem Bakulin: Vibronic coherence reveals dark multiexciton states mediating singlet fission in pentacene and its derivatives

Abstract

“Exciton fission, the spin-allowed conversion of a spin-singlet exciton to two spin-triplet ones, has been attracting increasing attention recently due to its potential for solar cell applications. However, despite numerous attempts to uncover the origin of fission’s ultimate speed and efficiency, the basic mechanisms at play are still debated. Particularly, in the core of the dispute lie the effects of coupling between electronic states and the role of the ‘multiexciton’ intermediate.

I will present a sub-15 fs 2D photon-echo spectroscopy study which we performed to elucidate the dynamics of excited states during fission process in films of pentacene and its derivatives. Our measurements demonstrate the abundance of long-lived oscillatory features in the data which we attribute to creating superposition of states in singlet as well as multiexciton vibronic manifolds. Our results indicate that matching and mixing of these vibronic manifolds is essential for understanding singlet fission dynamics.”