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Nanoparticle-based voluminous 3D networks with low densities are a unique class of materials and are commonly known as aerogels. Due to the high surface-to-volume ratio, aerogels and xerogels might be suitable materials for applications in different fields, e.g. photocatalysis, catalysis, or sensing. One major difficulty in the handling of nanoparticle-based aerogels and xerogels is the defined patterning of these structures on different substrates and surfaces. The automated manufacturing of nanoparticle-based aerogel- or xerogel-coated electrodes can easily be realized via inkjet printing. The main focus of this work is the implementation of the standard nanoparticle-based gelation process in a commercial inkjet printing system. By simultaneously printing semiconductor nanoparticles and a destabilization agent, a 3D network on a conducting and transparent surface is obtained. First spectro-electrochemical measurements are recorded to investigate the charge-carrier mobility within these 3D semiconductor-based xerogel networks.

A mononuclear FeII complex, prepared with a Bronsted diacid ligand, H2 L (H2 L=2-[5-phenyl-1H-pyrazole-3-yl] 6-benzimidazole pyridine), shows switchable physical properties and was isolated in five different electronic states. The spin crossover (SCO) complex, [FeII (H2 L)2 ](BF4 )2 (1A ), exhibits abrupt spin transition at T1/2 =258 K, and treatment with base yields a deprotonated analogue [FeII (HL)2 ] (1B ), which shows gradual SCO above 350 K. A range of FeIII analogues were also characterized. [FeIII (HL)(H2 L)](BF4 )Cl (1C ) has an S=5/2 spin state, while the deprotonated complexes [FeIII (L)(HL)], (1D ), and (TEA)[FeIII (L)2 ], (1E ) exist in the low-spin S=1/2 state. The electronic properties of the five complexes were fully characterized and we demonstrate in situ switching between multiple states in both solution and the solid-state. The versatility of this simple mononuclear system illustrates how proton donor/acceptor ligands can vastly increase the range of accessible states in switchable molecular devices.

Chemical modifications of the yet reported iron(II) compound [Fe(dpp)2(NCS)2]⋅Py (dpp = dipyrido[3,2a:2’3’c]phenazine, Py = pyridine) which shows abrupt spin crossover below room temperature with large hysteresis have been made. The purpose was to stabilize different spin states at room temperature as well as to adjust the spin crossover in temperature and hysteresis width. We modified the bidentate ligand dpp by substituting hydrogens at the phenazine by different functional groups. In addition, we substituted the thiocyanate monodentate ligands by NCSe−. The spin states of these compounds have been investigated by Mossbauer spectroscopy at two temperatures and temperature depending IR spectroscopy. These methods indicating that the chemical modifications are influencing the observed spin configuration of the complexes alongside the spin crossover behavior which changed to gradual and incomplete transitions. These promising results offer interesting possibilities for chemical adjustments of the shown spin crossover systems.

We synthesised a series of Iron(II)-triazole compounds and used the electrospinning procedure to incorporate spin crossover compounds (SCO) into polylactic acid polymer fibers. Composite fiber/SCO compounds of [Fe(NH2-trz)3](BF4)2 as well as [Fe(Htrz)2(trz)]BF4 were investigated via Mossbauer spectroscopy at 293 K and 77 K. The Mossbauer studies show that the spin crossover behavior is maintained in the polymer matrix.