Resolving the Fates of Multiple Triplet Excitons in Single Multi-Chromophoric Conjugated Organic molecules

University Of New Mexico, Albuquerque NM

Investigators

Abstract

Organic polymers are long chains of repeating molecular subunits. When they absorb light, some segments of the chain are placed in excited energy states that live for about a billionth of a second. However, a fraction of this energy can become trapped in lower energy states that last much longer, perhaps a thousand times longer. These longer-lived states can interact with each other, as well as excess charges existing on the chain, which poses significant challenges for using polymers in emerging technologies, such as light-emitting diodes and solar energy conversion devices. With support from the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Professor John Grey at University of New Mexico is studying these long-lived states over a broad range of time scales. Working with his students, Professor Grey is using microscopy methods that can observe single polymer chains to determine how the chain structure and packing influence these long-lived excitations. Their discoveries could inform the design of new polymers. In addition, Professor Grey, who is a veteran himself, is engaging with student veteran groups at the University of New Mexico to increase participation of veteran and non-traditional students in STEM fields though weekly 'lunch and learn' and tutoring sessions. The long-term goal is to improve enrollment and retention of student veterans by recognizing their unique experience and engaging them as leaders in classroom and laboratory settings. The project examines the population dynamics of spin-forbidden (triplet) excited states in multi-chromophoric conjugated polymers and molecular light harvesting arrays. Hybrid single molecule spectroscopy techniques and stochastic kinetic modeling are the primary physical probes used to resolve interactions between multiple triplets spanning time scales from approximately 1 ns up to steady-state conditions. The goal is to be able to count the number of triplets on a single molecule at any given time, and to resolve how these states and their interactions with other excited states evolve with increasing structural (morphological) complexity. This project also exposes new kinetic insights of bimolecular annihilation processes that are often difficult to measure reliably at the bulk material level. The research further utilizes collaborations with synthetic materials chemists to investigate how fine tuning of molecular structure impacts population dynamics of multiple interacting excited states. Student participants gain valuable skills in physical and materials chemistry as well as theoretical modeling vital for the advancement of National science and technology interests. 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.