Tailoring organic molecular structure to achieve singlet fission for photovoltaic applications

Solar energy is a key resource in the renewable energy sector, yet it does not fulfil its potential due to fundamentally restricted efficiency. Singlet fission has the potential to significantly enhance the efficiency of photovoltaic light harvesting beyond this Shockley-Queisser limit by transforming one higher energy photon into two lower energy photons. Despite almost a decade of research, the progress of this technology has been hindered by the limited selection of suitable molecules that can satisfy the strict energetic requirements for singlet fission to occur, with even fewer exhibiting optimal molecular packing and photostability for the process to be viable for real-world application.
Cibalackrots (derivatives of industrial indigo dyes), are highly attractive candidates for singlet fission due to their superior photostability, high extinction coefficient and ideal predicted triplet energy. While energetically viable, previous works suggest their non-ideal molecular conformation prevents efficient intermolecular orbital overlap required to facilitate singlet fission. This project aims to collaborate with chemists to elucidate if simple, judicious alterations in chemical structure of Cibalackrots can give rise to the elusive singlet fission potential desired without sacrificing molecular stability.
Characterising the underlying singlet fission dynamics is crucial in demonstrating how an improved molecular structure may positively affect the photophysics of these molecules. This will be achieved by using a wide range of cutting-edge techniques, such as ultra-fast femtosecond transient absorption spectroscopy, and electron paramagnetic resonance, alongside with X-Ray diffraction measurements. This cross-examination will aim to complement the understanding of the photophysics with analysis of the molecular packing structure. This will give a broader understanding of the consequences of molecular design, and test the hypothesis that we can tailor molecular structure to harness singlet fission for renewable energy application and a cleaner environmental future.