A Bottom-Up Approach to Rational Design of Molecular Materials
Organic donor-acceptor (D-A) co-crystals are a promising class of molecular materials for next-generation optoelectronic devices. High-throughput screening and machine learning methods employ structure-function relationships to predict combinations of donor and acceptor molecules with desired properties. However, optical properties of materials are particularly difficult to predict due to the computational expense of performing electronically excited state calculations. Furthermore, calculations of a molecular material’s radiative and non-radiative lifetimes cannot be straightforwardly computed from D-A cluster models, as orbital energy differences, couplings, and oscillator strengths differ substantially between the molecular dimer and a crystalline material. In this talk I present a novel approach to predicting radiative and non-radiative lifetimes in D-A co-crystals based on orbital structure-function relationships. The basis for this approach is the striking similarity of orbital character between the D-A dimer and D-A co- crystal, especially in the ground and first excited states. Furthermore, these orbital characteristics are related to the degree of charge transfer in different electronic states, which are key quantities for predicting radiative and non-radiative lifetimes. Here I present a novel metric for predicting the degree of charge transfer in the S1 (HOMO → LUMO) electronic state using ground state orbital analysis alone, enabling low cost predictions of radiative and non-radiative lifetimes in D-A co-crystals for future high-throughput screening approaches. We use this metric to correlate S1 charge transfer with internal conversion and intersystem crossing timescales in D-A co-crystals, measured with UV pump, UV-Vis probe ultrafast transient absorption spectroscopy (TAS). Non-adiabatic mixed quantum-classical dynamics (NA-MQC) calculations of D-A dimer models enable characterization of the ultrafast TAS signatures to unravel the complex physics underlying long exciton lifetimes in D-A co-crystals.
Dr. Laura McCaslin is a staff scientist in theoretical chemical physics at Sandia National Laboratories in Livermore, CA. Her research program specializes in studying the electronic structure, photochemistry, and dynamics of molecular systems. During her undergraduate studies at the University of California Berkeley, McCaslin performed research under the advisement of Prof. Martin Head- Gordon on the electronic structure of microsolvated ions. After completing a BS in Chemical Biology in Spring 2012, she began her PhD studies at the University of Texas Austin in Fall 2012. McCaslin performed research on the electronic and vibrational structure of small molecules under the advisement of Prof. John Stanton, completing her PhD in Fall 2016. She began a postdoc position at the Hebrew University of Jerusalem in January 2017 under the advisement of Prof. R. Benny Gerber, where she employed molecular dynamics calculations to study reactions at atmospheric aerosol interfaces. She began her independent research program at Sandia National Labs in Spring 2020, where her research in electronic structure and molecular dynamics has spanned many fields, including atmospheric chemistry, materials discovery and characterization, quantum control, and photodynamics.
Hosted by Professor Ilja Siepmann