Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene

Dithieno­[2,3-<i>d</i>;2′3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;4,5-<i>b</i>′]­dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F_<i>n</i>TCNQs, <i>n</i> = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the F_<i>n</i>TCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping (<i>t</i>_e^eff) are more than 10 times larger than the donor-to-donor hopping (<i>t</i>_h^eff). This is because the donor orbital next to the highest occupied molecular orbital makes a large contribution to the electron transport owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene

Dithieno­[2,3-<i>d</i>;2′3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;4,5-<i>b</i>′]­dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F_<i>n</i>TCNQs, <i>n</i> = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the F_<i>n</i>TCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping (<i>t</i>_e^eff) are more than 10 times larger than the donor-to-donor hopping (<i>t</i>_h^eff). This is because the donor orbital next to the highest occupied molecular orbital makes a large contribution to the electron transport owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene

Dithieno­[2,3-<i>d</i>;2′3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;4,5-<i>b</i>′]­dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F_<i>n</i>TCNQs, <i>n</i> = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the F_<i>n</i>TCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping (<i>t</i>_e^eff) are more than 10 times larger than the donor-to-donor hopping (<i>t</i>_h^eff). This is because the donor orbital next to the highest occupied molecular orbital makes a large contribution to the electron transport owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene

Dithieno­[2,3-<i>d</i>;2′3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;4,5-<i>b</i>′]­dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F_<i>n</i>TCNQs, <i>n</i> = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the F_<i>n</i>TCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping (<i>t</i>_e^eff) are more than 10 times larger than the donor-to-donor hopping (<i>t</i>_h^eff). This is because the donor orbital next to the highest occupied molecular orbital makes a large contribution to the electron transport owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene

Dithieno­[2,3-<i>d</i>;2′3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;4,5-<i>b</i>′]­dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F_<i>n</i>TCNQs, <i>n</i> = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the F_<i>n</i>TCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping (<i>t</i>_e^eff) are more than 10 times larger than the donor-to-donor hopping (<i>t</i>_h^eff). This is because the donor orbital next to the highest occupied molecular orbital makes a large contribution to the electron transport owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals

Benzothienobenzothiophene-Based Molecular Conductors: High Conductivity, Large Thermoelectric Power Factor, and One-Dimensional Instability

On the basis of an excellent transistor material, [1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)₂XF₆ (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room-temperature conductivity amounts to 4100 S cm^–1 in the AsF₆ salt, corresponding to the drift mobility of 16 cm² V^–1 s^–1. Owing to the high conductivity, this salt shows a thermoelectric power factor of 55–88 μW K^–2 m^–1, which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4<i>k</i>_F charge-density waves as an origin of the low-temperature insulating state

Benzothienobenzothiophene-Based Molecular Conductors: High Conductivity, Large Thermoelectric Power Factor, and One-Dimensional Instability

On the basis of an excellent transistor material, [1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)₂XF₆ (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room-temperature conductivity amounts to 4100 S cm^–1 in the AsF₆ salt, corresponding to the drift mobility of 16 cm² V^–1 s^–1. Owing to the high conductivity, this salt shows a thermoelectric power factor of 55–88 μW K^–2 m^–1, which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4<i>k</i>_F charge-density waves as an origin of the low-temperature insulating state

Benzothienobenzothiophene-Based Molecular Conductors: High Conductivity, Large Thermoelectric Power Factor, and One-Dimensional Instability

On the basis of an excellent transistor material, [1]­benzothieno­[3,2-<i>b</i>]­[1]­benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)₂XF₆ (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room-temperature conductivity amounts to 4100 S cm^–1 in the AsF₆ salt, corresponding to the drift mobility of 16 cm² V^–1 s^–1. Owing to the high conductivity, this salt shows a thermoelectric power factor of 55–88 μW K^–2 m^–1, which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4<i>k</i>_F charge-density waves as an origin of the low-temperature insulating state