Designing molecular materials for use as organic photovoltaics, molecular electronics, and photocatalysts is a multifaceted challenge requiring a detailed understanding of both the excited state energetics and the dynamics of charge and energy transfer. We address the dynamic challenge by developing new methods based on the path integral formulation of quantum mechanics that are uniquely suited to the simulation of photo-initiated excited state dynamics in the condensed phase. We then tackle the characterization of the excited state manifold in molecular systems using a combination of high-level electronic structure methods to accurately calculate excited state energies, normal mode analysis to quantify vibronic couplings, and novel orbital analyses to uncover structure-spectrum correlations.
In this talk, we focus on one target application: designing chromophores that exhibit ultrafast Singlet Fission (SF), a phenomenon that has the potential to significantly increase organic solar cell efficiency. We investigate SF in non-bonded and covalently bonded pentacene dimers: we uncover two distinct mechanistic pathways for ultrafast SF and we identify molecular geometries and bonding motifs that can be modified to enhance efficiency in each case. Finally, we combine the insights obtained from our theoretical investigations to generate a priori design principles for next-generation SF chromophores, and working with experimental collaborators, we verify them.

Nandini Ananth is an associate professor in the department of Chemistry and Chemical Biology at Cornell University. She received her bachelor's degree in Chemistry from Stella Maris College in Chennai, India, and a Masters in chemistry from the Indian Institute of Technology Madras.