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

Abstract

Terthiazoles with redox-active substituents like an N-methyl pyridinium group and ferrocene have been synthesized and their photo-and electro-chromic behaviors were investigated. The presence of two lateral N-methyl pyridinium substituents in the structure of terthiazole proved to be effective in inducing not only the reductive ring-closure of the terthiazole core but also its oxidative ring-opening reaction, leading to the first terarylene-based switch able to fully operate both photochemically and electrochemically. Moreover, the large increase in the redox potential between its open and closed form (700 mV) means that a part of the photon energy necessary to trigger the cyclization is stored in the form of chemical potential available for other works. Introduction of a second redox-active unit such as ferrocene onto the central thiazolyl moiety is found to inhibit the photochromism of the switch but not its redox switchability, which, instead, got improved for the ring-opening reaction via the redox properties of the ferrocenyl unit. The optical and redox properties of the switch in its different oxidation states are analyzed with the aid of DFT calculations in order to rationalize different switching processes.

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

“…As can be seen in Figure 2, the CV curve of 1 c 2+ (black line) features a one‐electron reversible reduction wave (as established using ferrocene as an internal standard, see Figure S7) at E 1/2 =−0.57 V (⊗ E p =80 mV) which fits well with data reported in the literature [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 .− ) and doubly‐reduced (DTE 2− ) 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] …”

“…Several studies have been specifically focused on the ring‐opening, [15–18] ring‐closing [19–22] or on the interconversion of dithienylethene (DTE) derivatives triggered by electrical inputs [23] . Similar redox‐triggered isomerization processes have also been reported for a series of dithiazolylethenes [11,14] and dithienylethenes [24,25] derivatives bearing pyridinium units. In all these reports, however, the underlying mechanisms, involving coupled electrochemical and chemical steps, were never thoroughly elucidated and therefore still remain unclear.…”

“…These photoisomerization processes can be achieved by irradiation at specific wavelengths (UV light for the open!closed isomerization and visible light for the back transformation) or under the effect of electrical stimulations. [4][5][6][7][8][9][10][11] The fast and reversible photoisomerization of diarylethenes has already been achieved both in solution and at the solid state with very high fatigue resistance and using irradiation wavelengths which can easily be tuned by chemical functionalization. [4][5][6][12][13][14] Several studies have been specifically focused on the ringopening, [15][16][17][18] ring-closing [19][20][21][22] or on the interconversion of dithienylethene (DTE) derivatives triggered by electrical inputs.…”

“…Diarylethene derivatives are particularly relevant for such applications due to their ability to undergo fully reversible light‐induced interconversions between an “open” form, featuring two virtually isolated aryl subunits, and a highly aromatic and rigid “closed” form. These photoisomerization processes can be achieved by irradiation at specific wavelengths (UV light for the open→closed isomerization and visible light for the back transformation) or under the effect of electrical stimulations [4–11] . The fast and reversible photoisomerization of diarylethenes has already been achieved both in solution and at the solid state with very high fatigue resistance and using irradiation wavelengths which can easily be tuned by chemical functionalization [4–6,12–14] …”

Recent advances in electrochemistry of pyridinium-based electrophores: A structronic approach

“…The fine-tuning of electrochemical properties of the dimers [9,11] can be set up by adjusting the following parameters: i) the inter-annular torsional angle (i.e. the degree of π delocalization) [12][13][14][15], ii) the connection scheme of the pyridinium rings [9], iii) the nature of the Npyridinio substituent (alkyl or aryl) [6] and iv) the nature of the intervening spacer (if any) [10,[16][17][18][19], which can be switchable [20,21].…”