Proton Catalysis in the Redox Responsivity of a Mini‐Sized Photochromic Diarylethene

Abstract

A thermally irreversible dithienylethene (DTE) photochrom can be turned into a thermally reversible one in presence of Cu(II) triflate. A ring opening (DTEC closed→DTEO open) occurs through the formation of a copper-containing fast transient intermediate. Stopped-flow experiments monitored at 410 and 780 nm have allowed to show that the stoichiometry of this intermediate is DTE/Cu=1:1. At longer monitoring times (i.e., several seconds after mixing), the intermediate undergoes a slow decay while the residual DTEC closed form opens. A joint detailed kinetic and electrochemical analysis has unveiled a proton catalysis scenario in which electron transfer between DTEC and Cu(II), ligand exchange, protonation-deprotonation equilibria of the cation radicals and ring opening are embedded into two main reaction cycles. At the beginning of the reaction, Cu(II) is reduced into Cu(I) and DTE is degraded without ring opening. Then, as the reaction progresses, the triflic acid released from the Cu(II) reduction switches-on a propagation cycle during which ring opens without any more Cu(II) consumption. Cyclic voltammetry, spectro-electrochemical measurements, delayed photocoloration experiments in presence of Cu(II) and acid-base additions have confirmed the main features of the proton catalysis.

Electrocarboxylation of Spiropyran Switches through Carbon‐Bromide Bond Cleavage Reaction

“…The low oxidation potential value obtained for the carboxylate BIPS‐COO − derivative is due to the aromatic electron rich system of the indole moiety. Similar anodic peak potential values were observed for other aromatic electron rich heterocycles, such as thiophenecarboxylate derivatives [50] …”

Photochromic Room Temperature Ionic Liquids Based on Anionic Diarylethene Derivatives

“…The pure diarylethene based RTILs ([ALIQUAT] 2 [DTE] and [P 6,6,6,14 ] 2 [DTE]) as thin films were prepared and studied by UV- ), involving first hydroxide anion exchange, followed by neutralization by means of an acid-base reaction using 1,2-bis(5'-carboxy-2'-methylthien-3'-yl)-cyclopentene. [29,30] [31] (313) 0.025 [31] (365) 1.44 [32] [o/o * + ] 0.85 [32] [c/c * + ] DTE 2À 0.67 [31] (313) 0.025 [31] (365) 0.87 [32] [o 2À /o * À ] 0.33 [32] [c 2À /c * À ] IL 1 0.23 [b] 2 [DTE] (colourless state) as pure RTILs showed two bands, one at shorter wavelengths as a well-defined peak at 258 nm followed by a small shoulder close to 300 nm. These results are similar to those obtained in solution (see supplementary information).…”

“…It is important to emphasize that in solution the photocyclization reaction is significantly faster compared to the RTIL. For several diarylethenes [2,33] and in particular for DTE, [31,32] formation of a by-product that diminishes the photochromic performance by affecting the photoswitching reversibility has been reported. Different approaches, such as varying the nature of the hetaryl moieties, the bridging units or the substituents, have been explored to suppress formation of this by-product and obtain highly fatigueresistance diarylethene-based photochromic systems.…”

Photocontrol of luminescent inorganic nanocrystals via an organic molecular switch

“…The resulting charged defect V O 0 is lying in the middle of the band gap and is thought to be responsible in part for the observed visible emission by the recombination of the electron from the conduction band (CB) with the hole hosted in the V O 0 defect. 34,47 An electron transfer from the DTE's HOMO level (located at À5.9 eV and À5.2 eV for the open and closed isomer respectively) 48 towards V O 0 is thus energetically favorable. It was demonstrated previously that ZnO Ncs coated with dodecylamine can exchange electrons despite the presence of the ligand layer.…”