Collaborative Research: The Impact of Mesoscale Structure on Multiexciton Dynamics of Macromolecules

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This collaborative project studies intimate details of the way organic polymers can be designed for uses in next-generation solar cells and other light-active electronic devices. One promising but unproven way of harnessing light-energy efficiently involves a special class of organic molecules that, when properly assembled, can recover energy that is normally lost as heat. However, organizing these molecules in the optimal way has proven to be a challenge, such that the beneficial impacts of this approach have not been realized to date. This project develops a new approach to assembling light harvesting molecules so that they are organized in a brush-like arrangement. The researchers use ultrafast cameras to study the flow of energy of the assemblies and use this information to optimize their structures. The discoveries that ensue from these studies can lead to transformative technologies for energy and information applications. The collaboration provides the participating students with opportunities to: develop interdisciplinary communication skills; work in teams; tackle challenges outside their respective core subject; disseminate their findings to chemists, physicists, and the community as a whole. The principal investigators focus on outreach activities targeting socioeconomically challenged communities in Harlem, NY, as well young chemists and postdoctoral scientists, with particular emphasis on those who belong to under-represented groups in science. Multiple exciton generation is now a rapidly growing area in photophysics that has yet to be acutely understood. The molecular version of multiple exciton generation is singlet fission – the generation of two independent triplet excitons from a single photon. From this light harvesting mechanism, unconventional exciton dynamics can be envisioned to exploit a) the amplification properties that result when two excitons/charge carriers are created from one photon (optoelectronics), b) the rapid population of spin correlated quantum states (quantum information), or c) the activation of localized multielectron reaction centers (photochemistry and photocatalysis). This proposal is rooted in fundamental studies of organic macromolecule structure-property relationships that govern the singlet fission multiexciton dynamics necessary for future implementations in device architectures. The researchers use a molecular engineering approach to control fundamental multiexciton dynamics and exciton transport across multiple length scales – from individual molecules (triplet pair formation processes) to nano-/micro-scales (free triplet formation and transport). Understanding the influence of the chemical nature of the chromophores themselves and their spatial arrangement, strategically tethered within macromolecules, provides the fundamental information necessary to solve some of the unifying and inherent challenges in developing next generation singlet fission device concepts.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.