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Proton Catalysis in the Redox Responsivity of a Mini‐Sized Photochromic Diarylethene
Author(s) -
Massaad Julie,
Micheau JeanClaude,
Coudret Christophe,
Serpentini Charles Louis,
Guirado Gonzalo
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201301566
Subject(s) - chemistry , catalysis , redox , photochemistry , protonation , deprotonation , cyclic voltammetry , photochromism , proton , electron transfer , electrochemistry , proton coupled electron transfer , catalytic cycle , inorganic chemistry , electrode , ion , organic chemistry , physics , quantum mechanics
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.