Aggregation dependent naphthalimide diimides for electrochromic windows

Randle, Rebecca (2022) Aggregation dependent naphthalimide diimides for electrochromic windows. PhD thesis, University of Glasgow.

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We describe the synthesis of naphthalene diimides (NDI) appended with simple amino acids and dipeptides. These systems can form a highly coloured reduced species by photo- and electrochemical reduction, which is reversible upon oxidation. In their neutral state these systems are transmissive and pale in colour. This transition from transmissive to coloured occurs quickly, using small potentials, and is reversible, making NDI systems a promising candidate for electrochromic devices. Their chromic properties, as well as their water solubility and tuneable aggregation, give such self-assembling small organic molecules many advantages over conductive polymers and transition metal oxides, which dominate the literature in this field. The behaviour of five NDIs in different pH solutions is explored, and we identify ideal aggregated states for each chemical structure (found by altering pH) and identify parameters of their ideal structures that stabilise the formation or stability of the reduced species. These parameters facilitating highest contrast between neutral and reduced states changes with chemical structure, highlighting the sensitivity and importance of aggregation. We also identify aggregate types consistent with poor chromic behaviour and use this information to explain poor colouration of one NDI system. Using neutron scattering we evaluate the long-term stability and cyclability of our best performing systems. Using in situ electrochemical techniques, we critically analyse our prior methodology and facilitate a truly representative measurement of the electrochemically reduced state of some NDI systems and analyse the susceptibility of NDIs to changes in aggregation with cycling between states. We report multicomponent systems using two NDIs mixed with a transparent low molecular weight gelator (LMWG) in different ratios and observe that the chemical structure of the NDI, the pH and the component ratio affects their aggregation and chromic properties. We observe the decrease and enhancement of radical anion formation upon reduction in different multicomponent systems and select certain systems to evaluate long-term use. A combination of diffusion and aggregation dependent factors contribute to the cyclability of these systems. Lastly, the effect of heat-cooling upon multicomponent systems is investigated. We find that different ratios of components respond differently. Radical anion formation and cyclability are affected. We identify different methods of improving cyclability (buffering, electrochemical scripting, multicomponent tuning) and open possibilities for future work using hydrogels with these multicomponent systems. At every point we try to understand and link aggregation types or parameters to desirable chromic properties such as colour intensity and efficiency of electrochemical processes.

Item Type: Thesis (PhD)
Qualification Level: Diploma
Colleges/Schools: College of Science and Engineering > School of Chemistry
Supervisor's Name: Draper, Dr. Emily and Adams, Prof. Dave
Date of Award: 2022
Depositing User: Theses Team
Unique ID: glathesis:2022-83096
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 Aug 2022 13:27
Last Modified: 24 Aug 2022 13:29
Thesis DOI: 10.5525/gla.thesis.83096
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