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Electron Transfer and Switching in Rigid [2]Rotaxanes Adsorbed on TiO 2 Nanoparticles
Author(s) -
Lestini Elena,
Nikitin Kirill,
Stolarczyk Jacek K.,
Fitzmaurice Donald
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100903
Subject(s) - viologen , rotaxane , chemistry , cyclic voltammetry , electron transfer , adsorption , electrochemistry , crystallography , photochemistry , supramolecular chemistry , organic chemistry , crystal structure , electrode
Bistable [2]rotaxanes have been attached through a bulky tripodal linker to the surface of titanium dioxide nanoparticles and studied by cyclic voltammetry and spectroelectrochemical methods. The axle component in the [2]rotaxane contains two viologen sites, V 1 and V 2 , interconnected by a rigid terphenylene bridge. In their parent dication states, V 1 2+ and V 2 2+ can both accommodate a crown ether ring, C, but are not equivalent in terms of their affinity towards C and have different electrochemical reduction potentials. The geometry and size of the tripodal linker help to maintain a perpendicular [2]rotaxane orientation at the surface and to avoid unwanted side‐to‐side interactions. When the rigid [2]rotaxane or its corresponding axle are adsorbed on a TiO 2 nanoparticle, viologen V 2 2+ is reduced at significantly more negative potentials (−0.3 V) than in flexible analogues that contain aliphatic bridges between V 1 and V 2 . These overpotentials are analysed in terms of electron‐transfer rates and a donor–bridge–acceptor (D–B–A) formalism, in which D is the doubly reduced viologen, V 1 0 , adjacent to the TiO 2 surface (TiO 2 –V 1 0 ), B is the terphenylene bridge and A is viologen V 2 2+ . We have also found that, in contrast with earlier findings in solution, no molecular shuttling occurs in rigid [2]rotaxane adsorbed at the surface. The observations were explained by the relative position of the viologen stations within the electrical double layer, screening of V 2 2+ by the counterions and high capacity of the medium, which reduces the mobility of the crown ether. The results are useful in transposing of solution‐based molecular switches to the interface or in the design and understanding of the properties of systems comprising electroactive and/or interlocked molecules adsorbed at the nanostructured TiO 2 surface.