Synthesis, Properties, and Redox Behavior of Tetracyanobutadiene and Dicyanoquinodimethane Chromophores Bearing Two Azulenyl Substituents

Abstract

Acetylene derivatives with an azulenyl group at both terminals have been prepared by palladium-catalyzed alkynylation under Sonogashira-Hagihara conditions. These alkynes reacted with tetracyanoethylene and 7,7,8,8-tetracyanoquinodimethane in a formal [2 + 2] cycloaddition-retroelectrocyclization reaction to afford the corresponding new tetracyanobutadienes (TCBDs) and dicyanoquinodimethanes (DCNQs), respectively, in excellent yields. Intramolecular CT absorption bands were found in the UV-vis spectra of the novel chromophores, and CV and DPV showed that they exhibited a reversible two-stage reduction wave, due to the electrochemical reduction of TCBD and DCNQ moieties. Color changes were also observed during the electrochemical reduction.

The [2+2] Cycloaddition‐Retroelectrocyclization (CA‐RE) Click Reaction: Facile Access to Molecular and Polymeric Push‐Pull Chromophores

“…Te trathiafulvalene (TTF) and extended TTF derivatives showed as imilar activity to monothiophene.H eating to reflux in 1,2-dichloroethane was necessary for the reaction to proceed, and the TCBD products were obtained in moderate yields (Table 1, entries 8a nd 9). [26,27] In particular, azulene derivatives showed av ery high activity,similar to the p-N,N-dialkylanilino donors.Thus, as eries of linear and branched oligo(ethynylazulene)s were prepared as precursors and their TCBD products synthesized in very high yields (Table 1, entries 10 and 11). [26,27] In particular, azulene derivatives showed av ery high activity,similar to the p-N,N-dialkylanilino donors.Thus, as eries of linear and branched oligo(ethynylazulene)s were prepared as precursors and their TCBD products synthesized in very high yields (Table 1, entries 10 and 11).…”

Azulene‐Based Donor–Acceptor Systems: Synthesis, Optical, and Electrochemical Properties

“…[55] The absorption band of 46 was ascribed to the quinoid resonance structure in the azulene moiety [43] in conjugation with the 2amino group, similar to that of TCBDs 22 and 28. [55] The absorption band of 46 was ascribed to the quinoid resonance structure in the azulene moiety [43] in conjugation with the 2amino group, similar to that of TCBDs 22 and 28.…”

Synthesis of 1,3‐Bis(tetracyano‐2‐azulenyl‐3‐butadienyl)azulenes by the [2+2] Cycloaddition–Retroelectrocyclization of 1,3‐Bis(azulenylethynyl)azulenes with Tetracyanoethylene

“…Bis(TCBD) 20 with two 2‐aminoazulene moieties, showed a strong absorption band at λ max =500 nm (Figure 6). Although the absorption maxima of bis(TCBD)s 15 – 20 were nearly equal to that of the corresponding mono‐TCBD derivatives 25 – 30 (Figure 7),12 the extinction coefficients show an increasing trend as the number of TCBD units. These effects exhibit an overlap of ICT arising from the resonance effect between the central 1,3‐azulendiyl core and two TCBD units as shown in Scheme .…”

“…25 From our previous study, 2‐ or 6‐azulenyl groups connected by π‐electron systems induce electrochromic properties with high reversibility, owing to the generation of stabilized anionic species 26. Moreover, electrochromic properties of the azulene‐substituted TCBD derivatives substituted by 1‐azulenyl groups with 2‐ or 6‐azulenyl substituents exhibited color changes with higher reversibility, attributable to the formation of the stabilized anionic species during the electrochemical reduction 12. Similar to the derivatives, alkynes 9 – 14 and bis(TCBD)s 15 – 20 might exemplify a new class of electrochromic materials with multiple electron transfer.…”

“…Recently, we have reported the synthesis and electrochemical properties of TCBD and DCNQ derivatives with azulenyl substituents, which have been prepared by the [2+2] cycloaddition–retroelectrocyclization reaction of the corresponding ethynylazulene derivatives with TCNE and TCNQ, respectively 11. Especially, TCBD and DCNQ derivatives substituted by a 1‐azulenyl group with either 2‐ or 6‐azulenyl functions showed rather high stability in the electrochemical redox cycles and improved electrochromic properties, over TCBDs and DCNQs substituted by two 1‐azulenyl groups, since the azulenyl substituent via its 2‐ or 6‐position tends to stabilize an anionic species formed by the electrochemical reduction reasoned by the contribution of their resonance structures 12. However, azulene derivatives with two TCBD units at both their 1‐ and 3‐positions have not, so far, been explored.…”