Fundamental investigations into photoswitchable imines (PSIs) and exploring their application in solar-energy storage

• Applicant: Dr. Jake Greenfield
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 556072458

The light-matter interaction of photochromic molecules has proven to be a robust method for off-the-grid solar energy storage, particularly in molecular solar thermal (MOST) systems. This research plan explores imine-based photoswitches, recently identified by our group, from a fundamental viewpoint (Focus A) and their application in energy storage and novel functional systems (Focus B). Specifically, we have discovered that arylimines can be engineered to exhibit useful photochromic properties, achieving near quantitative (>95%) conversion to the metastable Z-isomer with visible light and thermal half-lives of up to 19 hours at room temperature. The advantages of these imine-based switches over other established classes include the commercial availability of building blocks, scalable synthesis, and quantitative yields. However, our fundamental investigations into the structure-property relationship have been limited, and this proposal seeks to explore the chemical space available to these new photochromic units. Moreover, a key challenge for using these imines as MOST materials is improving energy storage properties while maintaining a reasonable thermal half-life, and we have identified strategies to address this challenge. Our proposal details four work packages (WPs). In WP1, by systematically exploring combinations of aldehyde and amine components, we aim to establish a comprehensive understanding of the structure-photoswitching property relationship and their propensity to store energy in the metastable state, in the context of MOST materials. In WP2, we will explore structurally similar ketimines, which offer handles for structural control and the potential for an inverted stability of the E/Z isomers, supported by preliminary investigations. Such inverted stability would be of interest in designing new photoswitches. WP3 will investigate how secondary dynamic-covalent interactions, specifically the formation of iminoboronates, can further tune the photoswitching properties and stabilities of the isomeric forms, with preliminary results showing promise in this approach. Finally, WP4 will explore the photoswitches in the context of MOST materials, aiming to identify their scope and improve figures of merit. We will investigate two strategies anticipated to increase energy storage without compromising the thermal half-life. Preliminary findings indicate that arylimines can photoisomerize in the condensed phase, exhibit negative photochromism, and possess good photo- and hydrolytic stability. In summary, this proposal focuses on exploring novel imine-based photoswitches. We seek to expand the toolkit of available photochromic compounds, identify motifs to tune photoswitching properties, improve energy storage in the metastable state, exploit these accessible materials in MOST applications, and identify new applications where these photoswitches excel. Our preliminary investigations in each of these areas provide confidence in our proposal.

• DFG Programme: Research Grants
• International Connection: United Kingdom