Bidirectional Ring‐Opening and Ring‐Closing of Cationic 1,2‐Dithienylcyclopentene Molecular Switches Triggered with Light or Electricity

Abstract

Either light or electricity can be used to trigger the reversible cyclization reactions of three bis(N‐methylpyridinium)dithienylethene derivatives that differ from each other by the presence of either thiophene rings or methyl groups at the two carbon atoms of the photoresponsive hexatriene system involved in forming the new C–C bond. All three derivatives undergo ring‐closing isomerization reactions when irradiated with UV light (365 nm) or when electrochemically reduced (–1.0 V). All three derivatives can also be ring‐opened by irradiating them with visible light (> 490 nm) or by electrochemically oxidizing them (+1.5 V). The presence of additional thiophene rings attached to the two C2 ring positions of the dithienylethene (DTE) backbone enhances the electrochromic behavior, while methyl groups in these positions results in improved photochromic performance. The nature of these groups also greatly affects the thermal properties of the compounds in their ground states. Replacing each methyl group at the C2 ring positions with a thiophene ring systematically lowers the activation energy of spontaneous ring‐opening by 8 kJ mol–1, which correlates with the enhanced efficiency of the oxidative ring‐opening reactions and with the limited photochromism of the thiophene‐functionalized derivative.

Photochromic and Reductive Electrochemical Switching of a Dithiazolylethene with Large Redox Modulation

“…The first example of a reductive ring‐closing reaction was reported for a dicationic dithienylethene,9 which was initially designed to demonstrate how its redox behavior could be modulated by controlling the electronic communication between the two terminal electroactive pyridinium groups through the photochromic reaction of the central dithienylethene linker 10. More recently, several related dithienylethenes with judicious structural modifications have been reported to display, for the first time, bidirectional electrochemical switching 11…”

Photochromic Diarylethenes Designed for Surface Deposition: From Self‐Assembled Monolayers to Single Molecules

“…[80] The charge transfer between surface and molecules is also important in the context of bistable compounds because the properties of the o and c forms in their charged radical states are different from their neutral ones. [28][29][30][31][32][33][34][35][36] Kim's group clearly demonstrated this when they showed that the c form is more stable than the o form in STM studies of 15 (Figure 7a) on metallic surfaces. Deposition and subsequent imaging of the assynthesized o forms resulted in the observation of both o and c forms, seen as extended and triangular lobes respectively, on Cu(111) at room temperature (Figure 7b).…”

“…The charge transfer between surface and molecules is also important in the context of bistable compounds because the properties of the o and c forms in their charged radical states are different from their neutral ones . Kim's group clearly demonstrated this when they showed that the c form is more stable than the o form in STM studies of 15 (Figure a) on metallic surfaces.…”

“…Nevertheless, other strategies for cycloreversion are also available: heating, [25] multiphoton absorption, [26] triplet sensitization, [27] and photo/electrocatalytic chain reactions. [28][29][30][31][32][33][34][35][36] Fourth, Irie and Uchida reported a diarylethene based on a benzothiophene where the aromatic groups have high fatigue resistance. [37] Hecht and co-workers found that electron withdrawing groups also increase fatigue resistance.…”

“…However, the high photocyclization quantum yield comes at a cost of low cycloreversion. Nevertheless, other strategies for cycloreversion are also available: heating, multi‐photon absorption, triplet sensitization, and photo/electrocatalytic chain reactions . Fourth, Irie and Uchida reported a diarylethene based on a benzothiophene where the aromatic groups have high fatigue resistance .…”