Oxidative and reductive cyclization in stiff dithienylethenes

Abstract

The electrochemical behavior of stiff dithienylethenes, undergoing double bond isomerization in addition to ring-closure, has been investigated. Electrochromism was observed in almost all cases, with the major pathway being the oxidatively induced cyclization of the open isomers. The influence of the ring size (to lock the reactive antiparallel conformation) as well as substituents (to modulate the redox potential) on the electrocyclization was examined. In the series of derivatives with 6-membered rings, both the E- and the Z-isomer convert to the closed isomer, whereas for the 7-membered rings no cyclization from the E-isomer was observed. For both stiff and normal dithienylethenes bearing benzonitrile substituents an additional and rare reductive electrocyclization was observed. The mechanism underlying both observed electrocyclization pathways has been elucidated.

New Insights into the Redox Properties of Pyridinium Appended 1,2‐Dithienylcyclopentenes

“…[13,26,36] However this result stand in sharp contrast with the electrochemical behavior of others DTE pyridinium derivatives reported in the literature, as dithiazolylethenes, [11,14] which show two reversible reduction waves attributed to the successive formation of mono-(DTE *À ) and doubly-reduced (DTE 2À ) derivatives. [14,25] Similarly, two electron-reduction waves were seen for the open and closed isomers of DTEs bearing strongly electron-withdrawing substituents such as benzonitrile. [25] In light of these quite different observations and conclusions, we were keen to thoroughly investigate and provide a clear-cut attribution of the chemical steps coupled to the oneelectron reduction observed of 1 c 2 + .…”

“…[14,25] Similarly, two electron-reduction waves were seen for the open and closed isomers of DTEs bearing strongly electron-withdrawing substituents such as benzonitrile. [25] In light of these quite different observations and conclusions, we were keen to thoroughly investigate and provide a clear-cut attribution of the chemical steps coupled to the oneelectron reduction observed of 1 c 2 + .…”

“…[24] Further investigations carried out on DTE analogs (dithiazolylethenes) conversely suggested that the addition of two electrons per DTE molecule is required to achieve such isomerization. [14,25] The only conclusion that can be drawn from these previous contributions is that the number of electrons involved in the electrochemical reduction of DTEs strongly depends on the type of skeleton and on its substitution pattern.…”

A Photo‐ and Redox‐Driven Two‐Directional Terthiazole‐Based Switch: A Combined Experimental and Computational Investigation

“…To date, most studies have focused on the electron-rich dithienylethenes and their oxidation induced ring-closing or ring-opening reaction depending on their substitution patterns. [3][4][5][6][7][8][9][10][11] In comparison, examples of reductive electrocyclization are rare and generally require the presence of strong electron withdrawing groups such as N-methylpyridinium connected to the photochromic dithienylethene or dithiazolylethene core. [12][13][14] However, recent works showed that dithienylethenes with appropriate cyano-substitution or an extended π system could also lead to reductive ring-closure, albeit with much more negative potentials.…”

“…[12][13][14] However, recent works showed that dithienylethenes with appropriate cyano-substitution or an extended π system could also lead to reductive ring-closure, albeit with much more negative potentials. [11] It is worth noting that in most cases the redox input triggers only one-way isomerization and cannot be used to bring the diarylethene back to its initial state. There are only few reports on bidirectional photo-and redox-switchable diarylethenes.…”