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

A new dipyridylthiazolylethene ( 1 a ) and its dicationic analogue ( 2 a ), with two N‐methylated pyridyl rings, have been synthesized and structurally characterized. Due to the N‐methylation of the pyridyl rings, 2 a displays not only very different photochromic properties, but also undergoes a reductive ring‐closing reaction to generate its closed‐ring isomer 2 b . Careful electrochemical studies coupled with EPR spectroscopy show that this reductive ring‐closing reaction takes place when 2 a is two‐electron reduced. DFT calculations suggest that such a ground‐state electrocyclization is driven by a very large stabilization of the reduced closed‐ring isomer 2 b relative to the reduced open‐ring isomer 2 a . In addition, 2 b exhibits two successive and reversible one‐electron reductions at half‐wave potentials of 0.04 and −0.14 V versus SCE and a redox modulation as large as 1 V is achieved when passing from 2 a to 2 b .