Carrier generation and electronic properties of a single-component pure organic metal

Abstract

Metallic conduction generally requires high carrier concentration and wide bandwidth derived from strong orbital interaction between atoms or molecules. These requisites are especially important in organic compounds because a molecule is fundamentally an insulator; only multi-component salts with strong intermolecular interaction-namely, only charge transfer complexes and conducting polymers-have demonstrated intrinsic metallic behaviour. Herein we report a single-component electroactive molecule, zwitterionic tetrathiafulvalene(TTF)-extended dicarboxylate radical (TED), exhibiting metallic conduction even at low temperatures. TED exhibits d.c. conductivities of 530 S cm at 300 K and 1,000 S cm at 50 K with copper-like electronic properties. Spectroscopic and theoretical investigations of the carrier-generation mechanism and the electronic states of this single molecular species reveal a unique electronic structure with a spin-density gradient in the extended TTF moieties that becomes, in itself, a metallic state.

Comparable charge transport property based on S···S interactions with that of π-π stacking in a bis-fused tetrathiafulvalene compound

“…Thus, in order to investigate the influence of oxygen on EM-TTP molecule, we further measured the electrical conductivity of EM-TTP crystal in vacuum condition. The results demonstrate similar I-V curves under ambient and vacuum (as shown in Figure 4(a)), indicating the high conductivity ascribed to the radical generation triggered by the protonation of the TTP moiety, not the oxygen doping effect [28,30]. To our knowledge, it is one of the highest conductivity to date reported for single-component organic conductor/semiconductor at room temperature [28,30], suggesting the potential applications of EM-TTP in Figure 3 (a, c) Schematic of two type EM-TTP micro-crystal device structures, one with two electrodes and conducting channel along the S··· S interaction direction, another type with two perpendicular conducting channels based on an individual crystal for anisotropic charge transport investigation; (b, d) optical microscopy images of the actual EM-TTP crystal devices constructed (color online).…”

“…One of the attractive advantages for TTF-based materials is their high conductivity [28,29], thus here we first examined their electrical conductivity based on the two-electrode devices at ambient conditions. Figure 4(a) shows the typical I-V curves of EM-TTP micro-crystals.…”

Cholesteric Aggregation at the Quinoidal-to-Diradical Border Enabled Stable n-Doped Conductor

“…The formation of free carriers in these neutral molecules from thermal activation through the small gap, as shown in low-band-gap quinone-bridged zwitterionic radicals, can also be argued to explain the conductor-like electrical response. [27][28][29] Electrical conductivities of n-doped films of the four 2D(QOT) using a commercially available n-type dopant N-DMBI have also been measured by the four-points probe method (the detailed doping procedure is shown in the Supplemental Information). The electrical conductivity of 2DQBT was increased from 4.9 3 10 À6 S cm À1 at 5 mol % to 1.36 3 10 À4 S cm À1 at the optimized dopant molar ratio of 10 mol % (Figure 2A; Table S3).…”

Mixed valence salts based on carbon-centered neutral radical crystals

“…For an example, the conductivity of insulating crystals of 1,4-phenylene-bis(dithiadiazolyl) diradical increased to σ RT = 100 S cm -1 by doping with iodine as an oxidant 21 . Furthermore, the connection of two TTF units through a π-electronic system effectively reduces U, and single component organic metals were realized in zwitterionic TTF dimer dicarboxylate radical 23 (σ RT = 530 S cm -1 , measured for a bulk sheet) and a transition metal complex with two TTF ligands 24 ([Ni(tmdt) 2 ], σ RT = 400 S cm -1 , measured for single crystal). High conductivities over several S cm -1 have been also realized in several single component bis(dithiolene)-type metal complexes [25][26][27] (σ RT = 750 S cm -1 at most 27 , measured for single crystal).…”