A new (TTF)₁₁I₈organic molecular conductor: from single crystals to flexible all-organic piezoresistive films

Abstract

This paper reports selective synthesis of two iodine-containing TTF (tetrathiafulvalene) salts: one, (TTF) 11 I 8 , is a new molecular conductor while another is the known non-conducting (TTF)I 3 compound. Single crystals of both salts were prepared using different amounts of iodine in the redox process between TTF and I 2 . X-ray data showed that the resulting conducting (TTF) 11 I 8 salt might be considered as a new modulated phase of the non-stoichiometric (TTF)I 0.7+d salts. The electrical resistance of single crystals of (TTF) 11 I 8 reveals a semiconducting-like behaviour. The paper presents also a study of electromechanical properties of organic conductive bi-layer (BL) films prepared by covering different organic polymeric films with a thin network of oriented submicrocrystals of (TTF)I 0.7+d phases. These BL films exhibit a combination of flexibility, lightweight, and high piezo-resistivity properties showing therefore a potential interest for electronic sensing applications where lightweight, large area coverage and flexibility are required.

Dynamic Resolution of Piezosensitivity in Single Crystals of π‐Conjugated Molecules

“…Development of purely organic π‐conjugated oligomers that are light, flexible and external‐stimuli responsive is highly desirable for multifarious applications in smart devices . Molecules that are capable of responding to external mechanical forces are sought after for human–machine or robotic interfaces, sensors, security inks, memory storage, and healthcare devices . In condensed forms like crystals, liquid crystals, or micelles, the piezosensitivity of a particular material depends extensively on its intermolecular interactions and packing, governed by H‐bonding, π–π, C−H⋅⋅⋅π, or dipole–dipole interactions .…”

“…When these interactions undergo alterations under mechanical perturbation, the emission spectrum or intensity may vary, which is regarded as mechanochromism or piezochromism and finds numerous practical applications . However, the innate complexities of intermolecular forces and structure factors render piezosensitivity of such systems unpredictable and their rational design and synthesis still remains a major challenge . In many cases, piezochromic molecules have appeared as isolated serendipitous occurrences where the change in luminescence is irreversible and achieving reversibility requires a subtle balance between different supramolecular interactions .…”

“…[1] Molecules that are capable of responding to external mechanicalf orces [2] are sought after for human-machine or robotic interfaces, sensors, security inks, memory storage, and healthcared evices. [3] In condensed forms like crystals, liquid crystals, or micelles, the…”

“…[5] However,t he innate complexitieso fi ntermolecular forces and structure factors render piezosensitivity of such systems unpredictable and their rational design and synthesis stillr emainsamajor challenge. [3,6] In many cases, piezochromic molecules have appeared as isolated serendipitous occurrences where the changei nl uminescence is irreversible and achieving reversibility requires as ubtle balance between different supramolecular interactions. [7] The indepthu nderstanding of the mechanism of piezosensitivity requiresi ts correlation with the structural changes occurring underp ressure, [8] which can be characterized by studying the single-crystal structure underh ydrostatic compression.…”

A Tetrathiafulvalene (TTF)‐Conjugated Microporous Polymer Network

“…Different iodide/polyiodide counteranions are observed in TTF iodide salts, which, however, can be controlled by the iodination method or the molecular structure of the TTF derivative 44. 54–58 To obtain the oxidized TTF moieties within the porous structure of TTFCMP, the network was stirred in an iodine/ethanol solution. We also observed that iodine doping can be carried out by iodine vapor diffusion into the porous networks.…”