Study of the Valence Tautomer Complex [Co(sq)(cat)(3-tpp)2] for Applications in Molecular Spintronics

Abstract

Molecular materials exhibiting bistability between two states are intriguing candidates for next generation electronic devices. Two similar classes of materials, known as spin crossover (SCO) and valence tautomers (VT) respectively, are of particular interest due to their multifunctional properties, which are controllable via several external parameters, such as temperature, light irradiation, pressure, magnetic field, and electric field. In recent years, considerable research has been dedicated to better understanding the underlying principles that govern the behavior of these materials, so that their implementation into nano-based devices might be achieved.

In this report, a systematic study of the valence tautomer molecule [Co(sq)(cat)(3-tpp)2] is presented. In the first chapter, the phenomenon of valence tautomerism (VT) occurring in coordination compounds is introduced and described from the perspective of Crystal Field Theory (CFT). Further, the molecular structure and physical properties of the [Co(sq)(cat)(3-tpp)2] molecule are explored. The properties of the ferroelectric material Polyvinylidene fluoride- hexafluoropropylene (PVDF-HFP), and the 2-D Mxene Ti3C2 are also discussed.

The next section details equipment development and experimental methods. Thin films of VT molecules were prepared from solution via a drop-casting approach. For thin film analysis, we have developed a custom made, fully automated Vibrating Sample Magnetometer (VSM) with a sensitivity on the order of 1 × 10-5 emu, as well as a fully automated, variable temperature, under vacuum electron transport stage, and a magneto-optic Kerr effect apparatus (MOKE). Additional experimental methods used to characterize the VT thin films include X-ray Absorption Spectroscopy (XAS), UV-visible Spectrometry (UV-Vis) and Differential Scanning Calorimetry. Experimental results obtained from these techniques are discussed and analyzed in the third section. PVDF-HFP polarization dependent isothermal spin state switching of [Co(sq)(cat)(3-tpp)2] is also discussed as well as the effects of doping [Co(sq)(cat)(3-tpp)2] with Ti3C2, followed by a conclusion and an outline of future work.