Mechanochemical Processing of Highly Conducting Organic/Inorganic Composites Exhibiting Spin Crossover–Induced Memory Effect in Their Transport Properties

Abstract

Bistable multifunctional materials have great potential in a large variety of devices, from sensors to information units. However, the direct exploitation of spin crossover (SCO) materials in electronic devices is limited due to their very high electrical resistance (insulators). Beyond their intrinsic properties, SCO materials may also work as probes to confer bistability as switchable components in hybrid materials, as controlled by external stimuli acting upon the SCO spin state. Low resistance conductors with memory effect may be obtained from the incorporation of SCO probes into a conducting organic polymer matrix. This strategy appeared to be limited by the strict synthetic conditions, since polymerization reactions are harsh enough to attack the redox‐unstable SCO component. Because of this, just a few successful examples have been reported. Here a versatile processing protocol is introduced to obtain SCO/conducting polymer composites exploiting a post‐synthetic mechanochemical approach that can be applied to any SCO component and any organic polymer. This new protocol allows highly conducting films of polypyrrole, polyaniline, and poly(3,4‐ethylenedioxythiophene) (PEDOT) to be obtained, with bulk conductivities as high as 1 S·cm−1, and exhibiting a thermal hysteresis in their electrical conductivity above room temperature.

Dynamical Mechanical Analysis and Micromechanics Simulations of Spin-Crossover@Polymer Particulate Composites: Toward Soft Actuator Devices

“…The dispersion of SCO particles inside polymers not only increases the processability of the materials but can also be the source of unprecedented properties thanks to the strain-driven coupling between the particles and the matrix. Hence, efforts into SCO composite mechanics have focused on utilizing the spin transition phenomenon in two waysgenerating movement in actuators − and creating strain-coupled hybrid materials that combine the characteristics of the constituents to achieve novel functionalities, − notably, transduction between heat and electrical energy. − …”

Thermal hysteresis of stress and strain in spin-crossover@polymer composites: towards a rational design of actuator devices

“…4–6 This huge transformation strain has motivated research to harness different forms of energy into useful mechanical work via the SCO phenomenon, with potential applications in robotic, biomedical and nano-technologies. 7–24…”

“…In this context, embedding SCO particles into polymer matrices provides a versatile means for exploiting this mechanical strain in actuating, 7,8,11–13,15–17,19,20,22,23 sensing 9,10,21 and energy harvesting 14,18 devices. Indeed, a polymer matrix allows for convenient processing the SCO material, such as dispersions of microcrystals, nanoparticles, nanorods or molecules, to obtain functional objects with arbitrary shapes at different size scales, including both macroscopic and micro/nanoscale devices.…”

Electronic structure of cobalt valence tautomeric molecules in different environments

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Isothermal voltage-controlled switching of the spin state has been demonstrated in Fe(II) SCO complexes, [24][25][26] opening a route to higher energy efficiency of non-volatile memory 26 and other types of electronic and sensing devices. [24][25][26][27][28] The conductivity of Fe(II)based SCO systems can be further enhanced by adding organic semiconducting polymers, such as polyaniline (PANI) and polar poly-D-lysine (PDL), 28,29 and select molecules. [30][31][32][33][34][35][36][37] Even interfaces can improve conductivity and mobility within adjacent SCO layers and it is likely that this also holds for valence tautomeric films.…”