Template Assembly of Spin Crossover One-Dimensional Nanowires

摘要

Spin crossover (SCO) is an important example of molecular switching, which can be realized by a wide variety of external stimuli. Many applications have been explored, including sensor and display technologies, and data storage. Much effort has been expended to develop the assembly of SCO complexes in materials and impressive results have been achieved with monodisperse nanoparti-cles, nanocrystals,thin films, micro- and nanopat-terned media, Langmuir-Blodgett (LB) films, and hys-teretic soft-media assemblies. Progress in this area was recently reviewed by Bousseksou et al., and the link between size morphology and switching characteristics was also examined. However a striking absence from this list is the ID nanowire. Magnetic nanowires have been cited by the magnetic recording industry as being important in overcoming difficulties in domain wall motion,and reliable thin-film etching and template-assisted electrodeposition routes to nanowires of magnetic metals have been established. However, preparation of nanowires of functional molecules by such methods is not possible, and wet chemistry routes are better employed. Melt-assisted template assembly methods have been effective for polymers and in favorable cases, nanowires of functional polymers show novel optical properties, including wave guiding and lasing. These nanowires are prepared by adding molten polymer to a nano- porous template, such as anodic aluminum oxide (AAO), followed by acidic or basic template dissolution. Preparation of polymer nanowires is also possible by using solution-assisted template wetting, and this method can be extended to include small molecules, but the acidic or basic treatment means that it is less suitable for fragile small molecules that would not survive dissolution of the template. However, by appropriate modification, insolubility in acids or bases may be conferred on functional small molecules such as mononuclear SCO complexes. To this end, we have investigated the potential of alkylated derivatives of Wilson's Fe(sal2-trien) complex, where sal2trien is the hexadentate N4O2 bisimino ligand;; formed by condensation of salicylaldehyde with N~3,N~2-bis(2-aminoethyl)-1,2-ethanediamine, to form nanowires by template assembly in nanoporous AAO, and describe herein the first reported SCO nanowires formed from Fe~(III)L(BF4)_(0.8)Br_(0.2)(1).