CAS: Symmetry breaking charge separation in far-red and near-infrared capturing chromophores: Minimizing the energy loss in the process of charge separation

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professor Francis D’Souza of the University of North Texas, Denton, TX, is building wide-band capturing chromophore dimers that can form excitonic states upon photo-illumination and undergo symmetry-breaking charge separation (SB-CS). Comprehending photoexcited charge transfer in molecular assemblies is of paramount interest as it directly relates to the process of light energy to chemical energy conversion, with direct applications in photocatalysis and building optoelectronic devices. By performing systematic experimental and theoretical studies, Professor D’Souza and his students will address the unanswered questions regarding the interplay between exciton dynamics and SB-CS, and the role of the molecular structure and geometry and solvent surroundings in governing these events. Achieving a strong visible-near-infrared spectral response in these highly absorptive dimers will be transformative to building high-efficiency devices while providing an excellent training platform for graduate and undergraduate students to help strengthen teaching, mentoring, and leadership skills. Photoinduced SB-CS is a process where a symmetrical pair of identical chromophores forms a charge-separated excited state with the hole and electron on different chromophores, and molecular systems exhibiting such a property are highly sought after owing to the minimal energy loss during the charge-separated state formation. However, a critical knowledge gap exists due to the lack of synthetic molecular dimers capable of undergoing SB-CS with low-energy light excitation from the far-red and near-IR regions. This study addresses this critical issue by building far-red and near-IR capturing chromophore dimers of different geometries and orientations and performing systematic studies at broad temporal and spatial time scales, to unravel the underlying mechanistic details of SB-CS and to derive meaningful structure-property relationships. The outcomes from this broad research project are expected to have a widespread impact across many fields of science. Additionally, the project provides advanced training opportunities for graduate and undergraduate research students, while also engaging local communities through Professor D’Souza's outreach activities. 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.