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

Abstract

We describe the synthesis and properties of azulene‐substituted 1,1,4,4‐tetracyanobutadienes (AzTCBDs) and heteroazulenyl TCBDs. TCBD derivatives were prepared in good to excellent yields through reaction of the corresponding 1‐ethynylazulenes with tetracyanoethylene (TCNE). In contrast, the reaction between propargyl alcohols and the 1‐azulenyl group in TCNE generated 2‐aminofuran derivatives, which were transformed into 6‐aminofulvenes with a 1‐azulenyl substituent upon treatment with several amines. The optical and electrochemical properties of the AzTCBDs were clarified by UV/Vis and voltammetry. The AzTCBD derivatives exhibited electrochromism, showing a multi‐step color change under electrochemical redox conditions. The multistage redox properties of AzTCBDs could be useful for the development of novel organic electronic materials.

Helicenes Grafted with 1,1,4,4‐Tetracyanobutadiene Moieties: π‐Helical Push–Pull Systems with Strong Electronic Circular Dichroism and Two‐Photon Absorption

“…The mono‐substituted systems 1 a , b show two reversible, well‐resolved 1 e − reduction steps centered on the tetracyanobutadiene unit at around −0.16 and −0.70 V vs. SCE, while the bis‐substituted 1 c displays four reversible 1 e − reductions, of which the third and fourth are very close in potential. These data are in agreement with results obtained for previously studied TCBD derivatives . The fact that 1 c exhibits a difference of 230 mV between the first and second reduction processes indicates either a significant electronic interaction between the two mono‐reduced TCBD fragments within the helical environment, which may be explained in terms of an increase in electron density on the helicene core after the first reduction event, or the presence of coulombic repulsion between negatively charged units.…”

“…1,1,4,4‐Tetracyanobutadienes (TCBDs) are known to be strong electron‐accepting groups that may give rise to donor–acceptor (push–pull) molecular structures when conjugated to donor fragments, and provide remarkably strong one‐photon absorption in the visible and red regions, along with nonlinear optical responses. , TCBDs possess electron‐accepting properties that are able to significantly tune the absorption features of molecules and, more generally, have a strong impact on the physical characteristics of the moieties they are linked to . Their synthesis implies a sequence of [2+2] cycloaddition–retroelectrocyclization (CA‐RE) between tetracyanoethylene (TCNE) and electron‐rich alkynes activated by donating groups (see Figure S1.0) .…”

“…, TCBDs possess electron‐accepting properties that are able to significantly tune the absorption features of molecules and, more generally, have a strong impact on the physical characteristics of the moieties they are linked to . Their synthesis implies a sequence of [2+2] cycloaddition–retroelectrocyclization (CA‐RE) between tetracyanoethylene (TCNE) and electron‐rich alkynes activated by donating groups (see Figure S1.0) . The identity of these donors varies, and the yield of the reaction strongly depends on their nature.…”

Development of Heterocycle-Substituted and Fused Azulenes in the Last Decade (2010–2020)

“…Therefore, many researchers have studied the synthesis, reactivity, and properties of these derivatives, as discussed below. Several review articles on the classical heterocycle-substituted and heterocycle-fused azulene derivatives have been published so far [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. However, there is no systematic review of the progress in the synthesis and reactivity of these derivatives within the last decade.…”

Antibacterial Polymeric Films Fabricated by [2+2] Cycloaddition–Retroelectrocyclization and Ag+ Ion Coordination

“…The [2+2] cycloaddition–retroelectrocyclization (CA–RE) of N , N ‐dialkylaniline‐substituted alkynes and 7,7,8,8‐tetracyanoquinodimethane (TCNQ) is a high‐yielding click chemistry‐type reaction that efficiently proceeds under mild heating conditions without any catalysts (Scheme S1, Supporting Information) . The products are N , N ‐dialkylaniline donor‐substituted cyclohexa‐2,5‐diene‐1,4‐diylidene‐expanded tetracyanobutadienes (charge‐transfer [CT] chromophores) featuring narrow bandgaps and potent redox activities.…”