Developing Structure-Function Relationships for Singlet Fission and Exciton Transport in Molecular Crystals via Selective Application of Strain

About This Grant

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professors Sean Roberts, Narayana Aluru, and Michael Cullinan of the University of Texas at Austin are combining sophisticated experimental and computational methods to study how strain affects singlet fission and energy transport in layered heterostructures. Singlet fission is a unique process wherein an energetically excited molecule shares half its energy with a neighboring molecule. This energy redistribution can enable improved systems for energy harvesting, photocatalysis, and quantum sensing, but achieving this goal requires an improved understanding of how a material’s structure impacts its ability to both undergo singlet fission and transport energy. Professors Roberts, Aluru, and Cullinan will address this challenge by developing micro-electromechanical (MEMS) devices that will be used mechanically strain molecular crystals to alter their internal structure. Computational modeling performed in concert with time-resolved microscopy measurements will identify how strain-induced changes in the structure of a crystal impacts its behavior to uncover structure-function relationships expected to guide the design of singlet fission materials for applications in energy harvesting and light detection. This project will support the training of three graduate students as well as two undergraduate student researchers from Austin Community College. Singlet fission enables individual photons to be transduced into pairs of spin-triplet excitons. However, developing technologies that utilize singlet fission to boost their performance requires singlet fission materials that direct the spatial transport of the triplet excitons they generate. To address this, a research team led by Professor Roberts will map how the structure of molecular crystals dictates their ability to undergo singlet fission and transport triplet excitons by using mechanical strain to systematically alter their intermolecular structure. By mapping how singlet fission and exciton transfer depend on a material’s structure, the research team will establish benchmarks for refining theoretical models for singlet fission and exciton transfer while simultaneously guiding the design of new compounds that can meet current challenges in energy harvesting. To achieve its objectives, the research team will employ MEMS devices to strain molecular crystals and thin film heterojunctions in concert with transient absorption microscopy experiments that will track exciton diffusion with femtosecond time resolution and tens of nanometers spatial resolution. These measurements will be modeled using electronic structure calculations that will both predict how materials deform under applied strain and how these structural changes impact a material’s ability to generate and transport triplet excitons. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.