How Do We Control Material Processes at the Level of Electrons? Progress on Grand Challenge New Horizons for Grand Challenge What parts of the Grand Challenge have been solved? We certainly have made tremendous progress in our ability to model and understand materials and material processes at the electronic level. Has the focus/scope of the Grand Challenge evolved? New research has demonstrated understanding of the direct electron conduction phenomena in single molecule systems. However as of yet we do not have clear pathway to broaden this understanding and to begin to build systems of molecules with controlled electrical properties. This opportunity could benefit from explicit discussion within the overall grand challenge. Remaining Challenge Refreshed Grand Challenge? • Does enough remain to be grand? Yes. • Is it tractable on the decadal scale or longer? Yes • Is a new statement of the Grand Challenge needed? Not at the broadest level. • Should the Grand Challenge be retired? No Submitted by: James Yardley Affiliation: Columbia University A Designer Polymer with 175% Singlet Fission Quantum Yield e h Scientific Achievement S1 CT 2xT1 The fundamental understanding of inter-molecular singlet fission processes is applied to the design of molecules that can undergo efficient intra-molecular singlet fission. The key requirements are 1) formation of a chargetransfer state immediately following excitation 2) the presence of a subunit with a low triplet energy such that ES≥2ET. Significance and Impact 1 nm Singlet Fission QY = 175% Top left: Electron (blue) and hole (red) density of the singlet state (S) in the strong acceptor-strong donor-strong acceptor (SA-SD-SA) molecule showing the charge transfer (CT) characteristics. Bottom left: Transient absorption spectra of the (-SA-SD-)n polymer showing the efficient singlet fission process, with triplet (T1) quantum yield of 175%. Right: a general design principle for intramolecular singlet fission in -SA-SD-SA- molecules. Erik Busby, Jianlong Xia, Qin Wu, Jonathan Z. Low, Rui Song, John R. Miller, X-Y. Zhu, Luis M. Campos, Matthew Y. Sfeir, “A General Design Strategy for Intramolecular Singlet Fission in Organic Materials,” Nature Materials (under in-depth review). The observation of intramolecular singlet fission yields up to 175% in this new family of materials provides insight into designed singlet fission materials using strong intrachain donor-acceptor interactions, which allow us to establish a new design framework for fission-capable materials. This provides a generalized platform for the development of tunable materials to address challenges of next-generation photovoltaic devices based on multiple exciton generation processes . Research Details Guided by mechanistic understanding, we combined molecular design and synthesis, first principles theory, and femtosecond spectroscopy to demonstrate a general principle for the development of toolbox for efficient singlet fission.