Measuring molecular excited states with spatial and temporal resolution

Research Group: 
Centre for Condensed Matter and Material Physics
Number of Students: 
Length of Study in Years: 
Full-time Project: 
Project Description: 
As a result of funding from the European Research Council (ERC), in 2012 and the ISIS muon group and Alan Drew designed, built and commissioned an upgrade to the HiFi muon spectrometer at ISIS with a high-power tuneable pulsed laser [1]. The primary output of the project was to demonstrate a new paradigm of muon spin relaxation (MuSR), specifically that it is possible to use muons to spatially and temporally map the evolution of molecular excitations on organic molecules. This first proof of principle was recently published in Nature Materials [2]. There are a number of specific research objectives to continue this research, below.

Objective 1: Understand how muons and/or muonium interact with excitations at the quantum level
We have strong evidence [2] that the primary mechanism of interaction is a change to the muonium-molecule reaction rate as a result of the molecular excitation, but there are open questions regarding the underlying mechanism of the interaction of muonium with molecular excitations. This will be clarified.
Objective 2: Develop new sample environments and experimental methodologies for photo-MuSR
We have recently demonstrated that ALC amplitudes in frozen dilute solutions of organic semiconductors are a factor of 20 higher than one would expect from the concentration. This makes it possible to measure donor molecules in a matrix of acceptors, using the bulk photo-MuSR spectrometer, thus mimicking a bulk heterojunction OPV. We will be uniquely able to study germinate pair formation and disassociation across donor-acceptor interfaces, with both spatial and temporal resolution.
Objective 3: Correlate molecular and electronic structure with excitation dynamics
We will investigate the non-trivial relationship between charge transfer states with electric dipole moments and molecular structure, using highly electron-deficient units to design molecularly hybridized push−pull materials. These materials will be fine-tuned via chemical substitution and functionalisation, and a complete understanding of the structure-function relationship will be developed. We will also work to identify the intermediary long-lived precursors to triplets in single fission (SF) materials.

[1] K Yokoyama et al., Rev. Sci. Inst. 87, 125111 (2016)
[2] K Wang et al., Nat. Mat. (2017); 10.1038/nmat4816
A good undergraduate degree in physics or related discipline.
SPA Academics: 
Alan Drew