Electrochromics by Intramolecular Redox Switching of Single Bonds

Abstract

Two moieties of mono- and trimethincyanines as well as those of styryl dyes were connected by a saturated alkyl tether made from compounds 3a-c, 5, 7, and 9a,b. In most cases, cyclic voltammetry and spectroelectrochemistry for these dyes together with the data for their monomeric models 4, 6, 8, and 10 reveal electrochemically irreversible transfer of two electrons but chemically reversible reaction and discoloration both on reduction and oxidation. Discoloration is interpreted as intramolecular formation of a single bond, which on redox breaking regenerates the starting colored species. Therefore, the investigated dyes exemplify a new general principle for electrochromics.

Electrochromics by Intramolecular Redox Switching of Single Bonds

“…Type OL/CS has recently been shown to be applicable by a series of examples. [1] This paper clearly demonstrates that the same is true for type OS/CL, in which the closed form provides the long-wavelength absorbing product. Both CϪC (OX-8 2؉ and OX-13 2؉ ) and NϪN (OX-16 2؉ , OX-22 2؉ , and OX-23 2؉ ) bond formation can be achieved.…”

“…This oxidative ring-closure is not restricted to entropically favorable transannular reactions (OX-8 2؉ , OX-16 2؉ , and OX-17 2؉ ), but also works with the formation of monocyclic rings (OX-13 2؉ , OX-22 2؉ , and OX-23 2؉ ) if a suitable ring size is achieved. In addition to electrochromic systems derived from the general structure of violene/cyanine hybrids, [12,18,19] type OL/CS [1] and type OS/CL represent another general structure in which the colored form consists of two closed-shell π-systems instead of the radical ions in classical organic electrochromic systems. [20] Electrochromic systems based on intramolecular ''no bond/single bond'' redox transformations according to Scheme 1 [21] offer further applications in ''molecular mechanics'', [22] due to the strong changes in geometry.…”

“…IR: PerkinϪElmer 1420 spectrophotometer. 1 H and 13 C NMR: Bruker AC 250 (250 MHz) and Bruker (600 MHz) spectrometers; standardized by solvent signals. MS: Varian MT CH7 and Finnigan MAT 8200 spectrometers.…”

“…150°C). 1 7, 12, 14, or 15 in dichloromethane (10 mL) were stirred for 2 h in the presence of acetic acid (10 mg) and molecular sieves (4 Å , 50 mg). The filtered solution was extracted with satd.…”

“…[1] In Part I of this series we dealt with the OL/CS type, in which the Open form displays Longwavelength absorption and the Closed one Short-wavelength absorption. The chromophores were mono-and trimethine cyanines and styryl dyes in which two units were tammograms (CV) and spectroelectrograms (SE).…”