Transcript How Do We Control Material Processes at the Level of Electrons? (J

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
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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.