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Details of Grant 

EPSRC Reference: EP/Y021525/1
Title: Anti-Kasha Materials: Myth or Photonics Paradigm
Principal Investigator: Meech, Professor S
Other Investigators:
Cammidge, Professor AN Jones, Dr G A
Researcher Co-Investigators:
Dr GG Bressan
Project Partners:
Department: Chemistry
Organisation: University of East Anglia
Scheme: Standard Research
Starts: 01 February 2024 Ends: 31 July 2026 Value (£): 815,901
EPSRC Research Topic Classifications:
Materials Characterisation Materials Synthesis & Growth
Physical Organic Chemistry
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
19 Sep 2023 EPSRC Physical Sciences Prioritisation Panel - September 2023 Announced
Summary on Grant Application Form
Photonic materials exploit the properties of light in delivering their specific function. Applications range from neuroscience (optogenetics) to molecular electronics for light harvesting via bioimaging and optical memories. In many cases, these materials exploit the unique properties of the electronically excited states of molecules, which are often distinct from those of the ground state, and can be created and detected with very high degrees of spatial and temporal precision. There are important rules that control the properties of excited states, and one of these is "Kasha's Rule", which was formulated over 70 years ago and in effect means that of all the accessible excited states only the lowest one will be useful in photonic materials. The higher lying excited states are too short lived, and relax in energy to the lowest state. Five years ago, this venerable rule was questioned by the observation in some molecules of unexpectedly strong "Anti-Kasha" emission (AKE) from higher excited states. If true this is very exciting, as it makes available new ranges of excited states for photonic materials applications, such that one molecule may be able to deliver two functions.

The initial reports of AKE gave rise to much controversy and confusion. Many remarkable AKE systems were proposed but quickly shown to be bogus, often due to impurities. However from the array of molecules considered, a number of apparently true and reproducible AKE sources were found. Inspection of these examples suggests that the common feature is that the wavefunctions (related to the probability of finding the electrons) of the lower and higher excited states are spatially separate. However, this tentative explanation is based on only a few isolated examples. To rigorously test this idea, and therefore to address the physical mechanism of AKE, requires a combination of molecular synthesis, advanced spectroscopy and theoretical and computational chemistry. Through synthesis we will develop a series of molecules in which we carefully control both the distribution of the lowest and second lowest excited state wavefunctions and the degree of coupling between them. Such control is achieved by developing molecules in which we couple a distinct pair of light absorbing molecules (to make a 'dyad') and and then modify the coupling between them by varying the bridging groups. Advanced time-resolved spectroscopy has two functions to fulfil. First it will measure the rate of relaxation out of the upper state of the dyad (which Kasha's Rule requires to be very fast) as a function of the molecular structure. Next we will apply recently developed two-dimensional electronic spectroscopy, which uniquely probes coupling between the two halves (or states) of the dyad. These spectroscopic observations as a function of dyad structure will be analysed through quantum chemical calculations of dyad wavefunctions and quantum dynamical simulations of two-dimensional spectra. The results of this theoretical analysis will inform the next round of synthesis and measurement as we seek to optimise the AKE phenomenon.

Overall this research program will yield a thorough understanding of the AKE phenomenon and thus indicate the true extent to which AKE molecules will be effective in the photonics applications proposed for them.
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