Silicon Surface‐Bound Redox‐Active Conjugated Wires Derived From Mono‐ and Dinuclear Iron(II) and Ruthenium(II) Oligo(phenyleneethynylene) Complexes

Abstract

Functional molecular materials are playing an everincreasing role in the fabrication of smart integrated devices that can perform inter alia logic operations. [1][2][3][4][5][6] As a result, the nano-engineering of molecular systems on surfaces has recently become a major focus of activity in the design and tailored construction of innovative materials. [7] The modification of conducting surfaces at the molecular level with redoxactive ''building blocks'' constitutes a powerful approach to the fabrication of such materials, particularly when the goal is integrated systems devoted to information storage or transfer. [8][9][10] For such applications, technologically relevant semiconducting surfaces, such as doped silicon, constitute particularly attractive substrates; indeed, silicon surfaces covalently derivatized with reversible redox-center-terminated organic monolayers [1,2,8,[11][12][13][14] have recently been prepared and examined to determine if molecular memories could result from such hybrid junctions. In parallel with these seminal studies, there have been relevant developments with redoxactive carbon-rich group 8 organometallics. These compounds are ideal candidates for reversible charge storage at the molecular level, [15][16][17][18][19][20] and recently Fehlner, Blum, and Rigaut have independently established that both homo-and heteropolynuclear representatives of this class of molecules can be anchored on conducting silicon [9,10] or gold [21,22] interfaces.The studies of bundles/monolayers on gold have revealed far better conduction through these organometallic substrates than through purely organic analogues of similar length, [21,22] while the studies on silicon surfaces have shown that a given redox state of the immobilized molecules can be generated by application of a suitably chosen electrical potential to this hybrid junction. [9,10] In complementary studies in the field of optics, [23] we have recently demonstrated that electrochemical generation of the various redox congeners of the dinuclear Fe(II)/Ru(II) complex 1 (Scheme 1) [24] provides a means to modulate the linear and nonlinear optical properties of a solution of these compounds. Taken together, these developments strongly suggest that hybrid junctions incorporating such carbon-rich molecules offer significant potential for realization of a variety of molecule-based devices. In view of these stimulating prospects, we report herein (i) the successful covalent assembly of electron-rich mononuclear Fe(II) (2 1 -2 3 ) and dinuclear Fe(II)/Ru(II) acetylides (3; Scheme 1) on monocrystalline silicon surfaces following a new and straightforward approach; and (ii) preliminary results defining the facile electron transfer between the semiconducting silicon surface and the immobilized redox-active molecules.To functionalize the silicon surface, we extended the hydrosilylation route developed for purely organic terminal alkynes [25] to organometallic substrates possessing a terminal alkyne moiety. Thus, solutions of the complexes 2 0 -2 3 [26] (...

Redox-Active Molecular Wires Derived from Dinuclear Ferrocenyl/Ruthenium(II) Alkynyl Complexes: Covalent Attachment to Hydrogen-Terminated Silicon Surfaces

“…3,4 In this connection, we have recently shown that complexes 1 n and 2 (Scheme 1) can be readily grafted onto Si−H surfaces through SiCC bonds. 25 Furthermore, the alkynederived monolayers obtained from 1 n 34 possess remarkably fast charge-transfer kinetics with the underlying silicon chip. 26 Due to the presence of interfacial vinyl bonds, the resulting monolayers are densely packed and are more ordered, and exhibit a higher surface coverage than alkene-derived monolayers, as previously demonstrated for purely organic substrates.…”

A simple synthesis of trans-RuCl(CCR)(dppe)2 complexes and representative molecular structures

“…The chemistry of transition metal complexes transRuCl(C"CR)(dppe) 2 is very well established [1][2][3][4][5][6][7][8][9][10], with a considerable body of recent research demonstrating the utility of these moieties in the construction of multimetallic complexes [11][12][13][14][15], optical materials [16][17][18], including those that exhibit pH or redox-switchable NLO response [19][20][21][22][23][24][25], colormetric [26] and fluorescent [27] sensing behaviour, the ''wire-like" behaviour that arises from extensive d-p mixing along the Ru-C"C fragment [28][29][30][31][32][33][34][35][36][37], and other characteristics that make these compounds potentially useful molecular electronic components [5,33,34,[38][39][40][41]. The facile replacement of the chloride ligand in complexes trans-RuCl(C"CR)(dppe) 2 either directly or from related vinylidenes with a second alkynyl ligand is well documented …”

Electron transport of bis(terpyridine)iron(II) complex wires on a semiconducting electrode

“…On another front, the electrochemical behaviors of redox active self-assembled monolayers (SAMs) on silicon electrodes have been investigated energetically because silicon is one of the essential semiconducting materials in the present electronics and expected as a promising electrode for molecular electronic devices [18][19][20][21][22][23][24]. The asymmetric charge transfer and the photoresponsive redox behavior have been caused by the semiconducting electronic properties such as dopant type, resistivity and band gap [25][26][27][28][29][30][31][32].…”