Molecular Design of Singlet Fission Materials: Harnessing the Potential of Diradical Character and Excited-State Aromaticity (EXAM-SF)

Nowadays, the sensitization of photovoltaic cells using singlet fission materials have attracted
tremendous interest in pushing the performance of silicon solar cells beyond their thermodynamic
efficiency limit. Multiple exciton generation process offers the possibility to surpass the ShockleyQueisser limit, allowing quantum efficiencies up to 200%. In this proposal, we exploit the multiradical
character combined with the aromaticity concept to manipulate the excited-state energy levels and
stability of quinoidal oligothiophenes and covalent dimers. The overarching goal is to establish a
novel conceptual framework to identify operative singlet fission chromophores with enhanced
stability. To assess excited-state aromaticity, advanced quantum chemical calculations will be
performed based on electronic and magnetic descriptors. A crucial aspect involves the experimental
characterization of the singlet fission process using ultrafast time-resolved techniques to assess the
distinct properties of the triplet pair state and the evolution of undesired deactivation pathways. To
accelerate the discovery of optimal functionalizations and explore the chemical space, inverse design
approaches will be implemented to devise quinoidal materials with the desired excited state
properties. On the generated database, general design criteria will be devised, including the role of
diradical character and aromaticity on the properties of excited states.