The molecular origin of Frenkel biexciton binding

Frenkel excitons are primary photoexcitations in molecular semiconductors and are unequivocally responsible for their optical properties. However, the spectrum of corresponding biexcitons - bound exciton pairs - has not been resolved thus far in organic materials. We correlate the energy of two-quantum exciton resonances with that of the single-quantum transition by means of nonlinear coherent spectroscopy. Using a Frenkel exciton model, we relate the biexciton binding energy to the magnitude and the sign of the exciton-exciton interaction energy and the inter-site hopping energy, which are molecular parameters that can be quantified by quantum chemistry. Unexpectedly, excitons with interchain vibronic dispersion reveal intrachain biexciton correlations, and vice-versa. The details of biexciton correlations determine exciton bimolecular annihilation, which is ubiquitous in organic semiconductors. It is crucial to quantify these interactions in order to establish a quantum-mechanical basis for their rate constants. Our work enables new opportunities for general insights into the many-body electronic structure in molecular excitonic systems such as organic semiconductor crystals, molecular aggregates, photosynthetic light-harvesting complexes, and DNA.Comment: 4 figures and Supplementary Material

Three Minute Thesis (3MT) 2021

Presented online April 9, 2021, 3:00 p.m.-4:40 p.m.Since 2015, Tech’s version of this international competition, which started at The University of Queensland, Australia, has provided graduate students with an opportunity to hone their professional skills and win prize money to help further their research efforts. The competition challenges students to explain their research in three minutes in a way that anyone can understand.Hosts (Members of Georgia Institute of Technology): Jeff Garbers, Enterprise Innovation Institute, Venture Lab; Bonnie H. Ferri, Vice Provost for Graduate Education and Faculty Development; James Black, Assistant Director of Strategic Initiatives and Grad Life, Office of Graduate Studies; and Leslie Sharp, Dean of the Library.Judges: Ashley Bush, Director, Communications and Employee Engagement, Southwire Company, LLC; Duffie Dixon, Owner, Duffie Dixon Media; Charles Edwards, Coaching Practice Lead, Jackson Spalding; Dene Sheheane, President, Georgia Tech Alumni Association; and Brian Yablunosky, Senior Manager, Digital Channels, Global Communications VMWare.Participant and PhD Division Winner ($2000 Travel Grant): Saad Javaid, Materials Science and Engineering; Advisor: Christopher Muhlstein; TITLE: “Ultra Vision and Time Manipulation: Technology Inspired Superpowers for Studying Cracks”.Participant: Hohyun Lee, Mechanical Engineering; Advisor: Costas Arvanitis; TITLE: “Minimally Invasive Targeted Drug Delivery in the Brain Enhanced by Closed-Loop Focused Ultrasound Control”.Participant: Hangmo Li, Materials Science and Engineering; Advisor: Natalie Stingelin; TITLE: “Plastics That Can Conduct Electricity: How Can They Impact Our Life?”Participant and PhD Division, 3rd Place ($1000 Travel Grant) AND People’s Choice Award (500 Travel Grant): Megan McSweeney, Chemical and Biomolecular Engineering; Advisor: Mark Styczynski; TITLE: “AptaTrigger: A Novel Biosensor Platform for Point-of-Care Diagnostics”.Participant: Mohammad S. E Sendi, Biomedical Engineering; Advisors: Babak Mahmoudi & Robert E. Gross; TITLE: “Personalized Deep Brain Stimulation: A Window of Hope for Depression”.Participant: Yifeng Shi, Chemical and Biomolecular Engineering; Advisor: Younan Xia; TITLE: “Shape-Controlled Pd Nanocrystals: Surface Science and Catalytic Applications”.Participant: Andrew Tricker, Chemical Engineering; Advisor: Carsten Sievers; TITLE: “Cracking the Case of Sustainable Fertilizzers: Ambient Ammonia Synthesis via Mechanocatalysis”.Participant: Jelly Vanderwoude, Biological Sciences; Advisor: Stephen Diggle; TITLE: “Discovering Novel Genetic Markers of Antibiotic Resistant in Cystic Fibrosis Lung Infection of Pseudomonas Aeruginosa”.Participant: Young Hee Yoon, Chemical and Biomolecular Engineering; Advisor: Ryan P. Lively; TITLE: “Understanding and Controlling Co-Transport of Water and Organic Solvents in Microporous Carbon Molecular Sieve (CMS) Membranes”.Participant and PhD Division, Runner Up (1500 Travel Grant): Muhammad Saad Zia, Electrical and Computer Engineering; Advisors: Mary Ann Weitnauer & Douglas M. Blough; TITLE: “Mitigating Beam Alignment Errors in Millimeter-Wave Communications to Go Beyond 5G”.Participant and Master’s Division: Winner ($1000 Travel Grant): Clara Glassman, Medical Physics; Advisors: Lisa Krishnamurthy & C. K. Wang; TITLE: “Creating the Google Maps of Brain-Behavior Relationships: A New Look at Post Stroke MRIs”.Runtime: 54:33 minutesFor the first time, the final round of Georgia Tech’s annual Three Minute Thesis (3MT) Competition will be held virtually. Ten Ph.D. students and one master’s student (who was awarded first place in the master’s category and will be competing for the People’s Choice Award) made the cut to participate in the finals