Tetrathiafulvalene-Tetracyanoquinodimethane Charge-Transfer Complexes Wired to Carbon Surfaces: Tuning of the Degree of Charge Transfer

Abstract

International audienceCharge-transfer complexes involving tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) derivatives are engineered in a 2D arrangement onto a carbon surface through the exposure of immobilized TTF units to TCNQ compounds. TTF molecules were immobilized as robust monolayers on carbon surfaces using the electrografting method followed by a click chemistry coupling. When the TTF monolayer is exposed to TCNQ TCNQF(2) (2,5-difluoroTCNQ), and TCNQF4 (2,3,5,6-tetrafluoro-TCNQ), strong donor acceptor complexes are formed onto the surface. A considerable decrease of the electrochemical response accompanies the formation of the charge-transfer complex. This observation is rationalized by the analysis of original crystal samples using an ultramicroelectrode cavity, confirming that charge transfer complexes are electrochemically silent. A fine control of the degree of charge transfer with the judicious choice of different acceptors is evidenced through electrochemical and X-ray photoelectron spectroscopy (XPS) measurements. Thus, donor acceptor complexes of different natures are formed. A fully ionic charge-transfer complex is formed upon exposure of the TTF monolayer to the more oxidizing TCNQF(4), while a neutral complex is obtained after exposure to the less oxidizing TCNQ, Exposition of the TTF monolayers to the intermediate TCNQF(2) yields a mixture of neutral-ionic systems. These donor acceptor interactions that fully mimic those described in the solid state are rarely described in such a 2D arrangement, with systems being directly wired to an electrode

A post-functionalization toolbox for diazonium (electro)-grafted surfaces: review of the coupling methods

“…114 These azide-or alkyne-modified surfaces react efficiently and rapidly with compounds bearing an acetylene or an azide function respectively, thus forming a covalent 1,2,3triazole linkage by means of click chemistry. This approach, compatible with a myriad of electroactive groups, has been exploited to immobilize ferrocene, 105, porphyrin, 142 phthalocyanin, 113,[143][144][145][146] tetrathiafulvalene, 147 fluorene, 148,149 BODIPY, 150,151 metallic complexes, 85,[152][153][154] TEMPO 155 or nitrophenyl derivatives. 138 The role of the redox probe varies according to the nature of the studies undertaken.…”

“…8). 147 The mild conditions required for the anchoring of the entities by click chemistry make it a very convenient method for the immobilization of biological material, mainly for the development of biosensors. This way has led to the elaboration of DNA (or aptamer), 129,[161][162][163][164] enzyme, 114,141,165,166 non enzymatic protein, 167 peptide 136 or amino acid 168 -modified surfaces.…”

“…Whether they are carried out in one direction or another (azide surface and alkyne in solution, or the opposite), the couplings are made under similar operating conditions. Cupper(I) is always used as a reaction catalyst (directly added, 134,148,162,173,175 or formed in situ from cupper(II) and a reducing agent 85,105,[113][114][115]119,[121][122][123][124]127,128,132,135,139,140,142,147,149,157,158,160,[163][164][165][166]168,177,178 or electrochemically generated 137,176 ). The most common option relies on the combined use of copper(II) sulfate and ascorbic acid (or sodium ascorbate, usually in excess) as reducing agent.…”

“…Indeed, terminal alkyne can easily be protected with silyl groups; this pathway has been exploited by the authors to graft bulky diazoniums avoiding the formation of multilayers. 115,116,119,122,123,127,128,147,149,177 The protecting group, which is compatible with diazonium electroreduction is then cleaved on the surface, allowing the post-reaction with an azide function. This strategy has been first validated by the electroreduction of a triisopropylsilyl (TIPS)-protected ethynyl aryldiazonium salt and the subsequent immobilization of azidomethylferrocene, after TIPS deprotection.…”

Solvent-tuned charge-transfer properties of chiral Pt(ii) complex and TCNQ˙− anion adducts

“…38,39,43 Moreover, ion-, vapor-, mechano-, and photo-induced multi-dimensional switches have been reported, and different conformations, alternating stackings and intermolecular CT capabilities can be modulated under specic stimuli. [44][45][46] In general, the TCNQc À anion interacts with other cations to form CT adducts through p-p and hydrogen-bonding interactions; CT adducts containing Pt(II) complexes and TCNQc À would be of special interest because effective Pt-p contacts may be found, therefore leading to more interesting spectroscopic, magnetic and conductive properties. 47 Due to intensive charge transfer interactions between Pt(II) complexes and TCNQc À , their adducts exhibit continuous UV-vis-NIR absorptions spanning ca.…”