Thin deposits and patterning of room-temperature-switchable one-dimensional spin-crossover compounds.

We present a study on thin deposits and patterning of 1-D spin-crossover compounds Fe(II)-(L)(2)H](ClO(4))(3)·MeOH [L = 4'-(4'''-pyridyl)-1,2':6'1''-bis- (pyrazolyl) pyridine] (1) that exhibit a reversible, thermally driven spin transition at room temperature. Micrometric rodlike crystals of 1 on silicon surfaces are achieved by drop casting and solvent annealing. We observed that the crystallinity of thin deposits and spin-transition properties critically depends on the deposition procedure. Furthermore, we proved processability and patterning using unconventional wet lithography that reduces the crystallite formation time by 1 order of magnitude. Thin deposits of 1 were characterized by atomic force microscopy, polarized optical microscopy and X-rays, and the switching properties were characterized by Raman spectroscopy.

Self-organization of rotaxane thin films into spatially correlated nanostructures: morphological and structural aspects.

The self-organization of rotaxane thin films into spatially correlated nanostructures is shown to occur upon a thermal stimulus. The mechanism of formation of nanostructures and their organization has been investigated using atomic force microscopy, bright field transmission electron microscopy, selected area electron diffraction, and molecular mechanics simulations. The evolution of the nanostructures follows a complex pathway, where a rotaxane thin film first dewets from the substrate to form nanosized droplets. Droplets coalesce by ripening, generating spatially correlated motifs. In a later stage, the larger droplets change shape, nucleate, and coalesce to yield crystallites that grow into larger crystals by incorporating the surrounding droplets. The results show the following: (i) the nanostructures represent a metastable state of a crystallization process; (ii) spatial correlations emerge during ripening, but they are destroyed as stable nuclei are formed and crystallization proceeds to completion; iii) crystallization, either on graphite or amorphous carbon films, leads to a precise basal plane, viz. (010), which has minimum surface energy. The inherent degrees of freedom permitted in the rotaxane architecture favors the re-organization and nucleation of the film in the solid state. Low-energy trajectories leading to crystallites with stable surfaces and minimum energy contact plane are found to occur via concerted, small amplitude, internal motions without disruption of packing and intermolecular contacts.