Heterocycle-based redox active, electrochromic organic materials

ELECTROCHROMIC MATERIALS represent a special and intriguing class of redox active compounds, characterized by a drastic change in their optical properties upon reduction or oxidation. Many aromatic organic molecules, monomeric or polymeric, are electrochromic, and some of them can even outperform their inorganic counterparts in some aspects. In particular, the ability to easily tune the colour of the redox states, represent an invaluable asset of this class of compounds. Among the many different organic electrochromic materials, those possessing a highly transmissive colourless state have gained much attention for their potential application in smart windows, self-darkening eyeglasses, anti-glare car rearview mirrors, etc. Moreover, a neutral tint of the coloured form is desired for these applications in order to avoid colour distortion. This work develops a novel class of discrete and polymeric electrochromic materials based on the violene structural motif. In particular, the class of diazinium ethenes has been explored and the electrochromic properties of the derivatives have been evaluated by electrochemical measures. These compounds have shown to undergo a reversible two-electron transfer, accompanied by a colourless −)−−*− coloured electrochromic behaviour with high contrast in the 450-550nm region. The new violene discrete electrochromes were then incorporated in a poly(3,4- ethylenedioxythiophene) (PEDOT) matrix, developing an hybrid multichromophoric system that take advantage of the characteristics of both systems to achieve a panchromatic absorption in the reduced state and a very high contrast value. In particular, the incorporation of the violene electrochromes has been obtained linking them, through a tether, to an EDOT moiety, and subsequently polymerizing (chemically or electrochemically) themodifiedmonomers (ISOx). The obtained polymers, poly(ISOx), display colourless highly transmissive oxidized states and reduced states with an extended colour palette (violet-red, purple and brown). Moreover, an impressive electrochromic contrast in the visible region has been achieved, with calculated luminance variations as high as 72%. This result represent a big improvement compared to the literature reported 52% for a system with comparable spectral characteristics. In the last chapter, a novel and versatile synthon for EDOT derivatization, exo-methylene-EDOT, is described and characterized along with some of its derivatives. This compound readily react with alcohols under acid catalysis to give Markovnikov addition products, and with thiols, in presence of radical initiators or photochemically, to give sulfides (anti-Markovnikov products). The latter reactivity proved to be very interesting for the extreme rapidity and high conversions achieved. An EDOT derivative with a pendant trialkoxysilane moiety has been prepared using 3-mercaptopropyltrimetoxysilane as thiol counterpart. This compound was subsequently tested as reagent for the functionalization of surfaces with EDOT moieties. An alternative approach, relying on an in situ thiol-ene reaction between exo-methylene-EDOT and a thiol functionalized surface, was also tested to achieve such functionalization. Both procedures have demonstrated to provide the desired surface modification. This kind of ultra thin films could find application as coupling layers for the deposition of PEDOT-like polymers on metal oxides, solving the adhesion problems that hamper the long-term operation of the devices.