The design of dual-mode photochromic and electrochromic 1,2-Dithienylcyclopentene dyes

Chemicals that interconvert between colourless and coloured states upon stimulation with light or electricity are key to development of modern optical filtering technologies. Such chemicals are found in photochromic lenses or electrochromic windows that darken when exposed to intense sunlight or by the flick of a switch, respectively. This thesis proposes the design of chemical dyes that change colour when exposed to both intense light and electricity: offering access to an advanced set of materials useful for designing dual-mode photochromic and electrochromic hybrid technologies. Photochromic 1,2-dithienylcyclopentene dyes (DTEs) reversibly interconvert between their colourless ring-open and coloured ring-closed forms upon irradiation with appropriate wavelengths of light. Recent findings have shown that DTEs are also electrochromic and change colours when they are subject to electrochemical oxidation. However, to date, the electrochromism of DTEs is not reversible. This thesis presents DTE derivatives that are capable of being toggled between multiple oxidation states and shows that reversible electrochromism of DTEs is achievable. The electrochemical reduction of a known bis(N-methylpyridinium) DTE is explored and is shown to undergo a ring-closing reaction using a combination of cyclic voltammetry and various spectroelectrochemical analyses. The bis(N-methylpyridinium) motif is then used to design and evaluate the electrochromic performance of three DTE derivatives that undergo reductive ring-closing and oxidative ring-opening reactions. All three DTEs undergo ring-closing isomerization reactions when irradiated with UV light or when electrochemically reduced. Conversely, all three DTEs are ring-opened by irradiation with visible light or by electrochemical oxidation. A structural dependence for the thermal, photochemical and electrochemical properties of the DTE derivatives is thoroughly investigated and discussed. The results of a collaboration to characterize the electrochemical properties of N-heterocyclic carbene (NHC) reagents and their corresponding imidazolium conjugate acid ions are also reported as an appendix. NHCs are most noted for their role as coordinating ligands in modern organometallic catalysts, while imidazolium ions are important to the design of ionic liquids. The results of these electrochemical studies show that 1) NHCs undergo electrochemical oxidation and are reducing agents, and 2) the electrochemical reduction of imidazolium ions is a convenient method to synthesize NHC reagents.