有機導電体における分子自由度
低温物質科学研究センター

矢持 秀起

・分子性導体の歴史・(EDO-TTF)2PF6の多重不安定性
超高速・高効率光誘起相転移
・分子の化学修飾と錯体の物性変化-1-Molecular Conductor ― Summarized History
1954 Organic Semiconductor• Br2

1980s: Organic Superconductors
H3 CSeSe

CH3

H3 CSeSe

CH3

Q1D Superconductors
max. Tc = 1.4 K (AP)1960s 1D Organic Metals
NC
CN
S
S
S

S

NC

Increment ofDimensionality

CN

S

S

S

S

S
S
S
S
2D Superconductors
max. Tc = 12.3 K (AP)1990s: 3D Molecular Superconductors

max. Tc = 33 K (AP)-2-

TTF•TCNQ - The First Organic MetalSSSS
TTF+NCCNNC

CNTCNQ(TTF)δ+(TCNQ)δδ = 0.56

38 K
54 K
Peierls gap
Peierls gap
In TTF chain in TCNQ chain
Semiconductor
Metal
-3-

Increasing the Dimensionality
Increment of side-by-side
intermolecular interaction

SS

S

S

H3CSe

Se

CH3

H3C

Se

Se

CH3

Atom Size

Numberof Atoms

TMTSF

S

S

S

S

S

S

S

S

TTF

BEDT-TTF (ET)-4-

TMTSF Superconductors-5-

BEDT-TTF Superconductors
SS

S

S

S

SS

S&muat ch mpreosen retFlexible-6-3-dimensional Superconductors

Alkali metals are in theinterstitial sites among C60's.
Max Tc = 33 K (RbCs2C60)-7-Summarized History

Increment of Dimensionality

1954 Organic Semiconductor

1980s: Organic Superconductors

• Br2

H3CSe

Se

CH3

H3CSe

Se

CH3

Q1D Superconductors
max. Tc = 1.4 K (AP)1960s 1D Organic Metals
NC
CNS
S
S

S

NC

CN

Molecular Degree of Freedom
Lattice point ≠ Simply a point√ Size√ Shape√ Functionality
OS

S

O

S
S
O
O
BEDO-TTF (BO)

O

S

S

S
S
O
EDO-TTF

SSSS

S
S
SS
2D Superconductorsmax. Tc = 12.3 K (AP)1990s: 3D Molecular Superconductors

max. Tc = 33 K (AP)-8-

BEDO-TTF(BO) SaltOSSOOSSO

Self-assembling Packing Pattern
a+2cCalculated Fermi Surface

3a+c

2D Layered Structure→ 2D Electronic StructureSide-by-side
Heteroatomic Contacts
Weak Hydrogen Bond Network

vdW
S•••S = 3.60 ÅS•••O = 3.32 Å

vdWH•••O = 2.72 Å-9-Partial Suppression of Self-assembling Nature of BO
OOSSSOOOOSSSOO

Flat Side Surface-OCH2CH2O→ Stable Metal
NO PHASE TRANSITION

obstruction
Introduction ofBulky Substituent
OS

SOOSSO

BEDO-DBTTF
OSSSO

SSS

EOET

Removal of an
EDO GroupO

SSO

SS

EDO-TTF- 10 -EDO-TTF Complexes
H 2C
H 2C

O

C S

C C

S CH

C S
S CH
O
EDO-TTF

At 2001 (when we started): Synthesis of donor
A few kinds of complexes: No description of composition
Conductivity: No description or ≤ 2 × 10-4 Scm−1+ TCNQ deriv.

→No Metal
No Self-assembling

A. Ota, et al., Mol. Cryst. Liq. Cryst., 376, 177-182 (2002)+ Inorg. Anions →Variety of Structure& Properties

2:1 ReO4, GaCl4
σRT = 130, 54 Scm-1
Activated behaviors ≤ 250 K
Different typed columns
A. Ota et al., J. Low Temp. Phys., 142(3/4), 425 (2006)

5:3 BF4σRT = 1 Scm-1 (Ea = 62 meV)

4:0.85:4(H2O) Sb2F11

σRT = 2 Scm-1 (Ea = 55 meV)

Multimer & monomer

A. Ota et al., in “Multifunctional Conducting
Molecular Materials”, eds. G. Saito et al., RSC
Publishing, Cambridge, UK. (2007), pp. 115-118.

- 11 -EDO-TTF — Preparation of PF6 Complex
Electrooxidation (Electrocrystallization)→(EDO-TTF)2PF6
EDO-TTF + (Bu4N)PF6/ EtOH
11.6 mg 68.1 mg 18 mL 0.5 µA
black
12 dayselongated platesb56501
A66501,02

A56501,02

76602

66602

65501

55501
A55501,02o
EDO-TTF was added to (+)
side only, while ca. half
amount of (Bu4N)PF6 wasadded to each chamber.

66501

A65501,02a

Head-to-Tail Stacking along b-axis.
Disordered Ethylene.
Isotropic Rotation of PF6-.

Triclinic P 1̄a = 7.197(0.9) Åb = 7.343(0.6)
c = 11.948(1)α = 93.454(7)°β = 75.158(6)γ = 97.405(7)V = 605.0(1) Å3
Z=1
R = 5.6 %kyYVΓkxXM
CAlmost Uniform 1D Intermolecular Overlap Integrals.
A. Ota et al., J. Mater. Chem., 12, 2600 (2002)- 12 -

Thermally Induced MI Transition of (EDO-TTF)2PF6

TMI ≈ 280 K
ρ jump: ca. 5 orderParamag. ↔ Non-mag.
First-order Transition- 13 -

How Metal-Insulator Transitions Occur
itinerant electrons
New periodicity byPeierls
CDWAnion
Ordering(orderdisorder)

Charge & Latticeforsm nin ioah sitce anMreT
O n O neSDW
On-site Coulomb (U)Charge density
CounterComponent
Spin Density
Localization byCoulomb repulsion

MottNO
ChargeOrdering

Neighbor-site Coulomb (V)NO- 14 -(EDO-TTF)2PF6 — Above and Below TMI (280 K)plθ
a1,nbeθa6nt r:.
0º 2 :: 1 0.
,01. 8º,.31º 2º, 7 .1º.9º

Distinct Molecular Deformation(Overlap Integral × 103)

Overlap
IntegralfromBondPF6Length Rotation

Uniform

0.5+

Isotropic

Alternate1+/0

Uniaxial

PeierlsChargeOrderOrdering Disorder

Molecular Deformation is regarded as theOrigin to Mix Metal-Insulator Transition
Mechanisms (Multi-instability).
- 15 -

(EDO-TTF)2PF6 − Other Properties −Raman Spectra: 4.2 K → Coexistence of 0.9+, 0.1+ Donors
O. Drozdova et al., Synthetic Metals, 133-134, 277-279 (2003).

Accurate Structure Analysis with MEM method:
285 K → +0.6(1)260 K → F: +0.8(1) , B: +0.2(1)S. Aoyagi et al., Angew. Chem. Int. Ed., 43(28), 3670-3673 (2004) .

Reflection Spectra: Significant Temperature DependenceO. Drozdova et al., Phys. Rev., B70(7), 075107-1-8 (2004) .

Calorimetry: Transition Entropy→ Unharmonicity of PF6 Rotation in RT Phase

K. Saito et al., Chem. Phys. Lett., 401(1-3), 76-79 (2005).

Uni-axial Strain: along c* → TMI↑ (> 60 K/4 kbar)

M. Sakata et al., Synthetic Metals, 153(1-3), 393-396 (2005).

Photo-induced Phase Transition:
Ultra-fast Highly Efficient, ~ 0.1 ps, 50 - 500 donors/photon
M. Chollet et al., Science, 307, 86-89 (2005).
- 16 -Photo-induced Phase Transition (PIPT)Time DelayPump
Probe
1.55 eV

Completes in ca. 1.5 ps
1 photon / 50-500 molecules

PIPT to Highly Conducting
Metastable Statevibration: ca. 0.5 ps/cycle at 180 K
Strong Electron-Lattice Interaction
M. Chollet et al., Science, 307, 86-89 (2005)- 17 -PIPT — Comparison with other systems
one photon

Our system
50 – 500 molecules
within ca. 0.1 ps
OO

S
S

SShνO

S

O
S

S
S

Insulator

cool

heat

Metal

RbTCNQ (Ins. - Metal)< 10 molecules, ca. 0.1 ps
TTF-Chloranil (Neutral - Ionic)
280-2,800 molecules, ∼1 ns

Ultra-fast & Highly Efficient PIPT
Controllable Initialization
Development of Phase Transition→ Dynamics of Non-equilibrium State- 18 -PI Metastable State ≠ RT Metallic Phase

Optical Conductivity (103 Ω-1cm)∆R/R

Simulated (simplemultilayer model)

HT phase (290 K)

0.1 ps after pump
one peak at low energy

Theoretical Calculation
H: t, U, V, γ (e-ph coupling∋ anion potential modulation)
time dependent model

LT phase (180 K) : (0110)

PIPT state: (1010) Charge Disp.
≠ RT Metallic (½ ½ ½ ½) Phase
Lattice potential:
fluctuated in this time scale
Wide Range Optical
Conductivity Spectra

K. Onda, S. Ogihara, K. Yonemitsu, N. Maeshima, T. Ishikawa, Y. Okimoto, X.F. Shao, Y. Nakano, H.
Yamochi, G. Saito, S. Koshihara, Phys. Rev. Lett., 101(6), 067403-1-4 (2008)- 19 -

After (EDO-TTF)2PF6 − Isotope Effect
OO

SSElectron-Phonon (ElectronMolecular Vibration) Coupling

SShν
O

SO
S

cool

heat

Metal

Isotope substitution→ Lattice (Molecular) Vibrations

SS

DOSS

D

EDO-TTF-d 2• Modulation of π-system(conduction path) vibrations• For PF6 & AsF6 complexes
d0 → d2: ∆TMI ≈ 3 K

321lSinaSd2origO

χ / 10-4 emu mol-1

Insulator

0260

270
T/K280(EDO-TTF-dx)2AsF6- 20 -

After (EDO-TTF)2PF6 − Anion Size EffectTM
Su I bysc Ma
ep gntib etilit icy

Isostructural (EDO-TTF)2XF6 (X = P, As Sb)

TMI↓

TMI↑

Size

TMI (K)ΔTMI (K)

PF6

279.0

1.0

AsF6270.8

5.5

SbF624214

スライド内容 一部削除
ここで観測された、転移温度とヒステリシス幅の陰イオン依存性については、現在、その詳細を解析中です。

- 21 -

Molecular Design Based on EDO-TTFOOSSSSDistinct Molecular Deformation
Multi-instability of Itinerant ElectronshνOSOS

coolheat

MetalSSTo Find Further Peculiar Systems
Similar π-electron system
Similar Molecular Size
Lower Symmetry

Insulator

EDO-TTF having Small Sized Substituent
OSS1) BuLi/THF -78°C

OOSS

2) CH3ISS
O
MeEDO-TTF(43 % yield)

EDO-TTF

S

S

CH3

cf. 17 % yield: A. Miyazaki et al., (2001)- 22 -O

SSOSSCH3Complexes

MeEDO-TTFAnion

D:Aσrt (S cm-1)

Compressed PelletsBF4

2:126 (Metal)

ClO4

2:124 (Metal)

PF6

2:1

3 (Semi.)AsF6

2:115 (MI at 240 K)

SbF6

2:1

6 (MI at 250 K)

HCTMM 4 : 1NCNC
NC

CNCN
CN

6 (Semi.)X.F. Shao et al., J. Mater. Chem., 18, 2131-2140 (2008)

2:1 PF6

σrt (S cm-1)

Black powder

3 (Semi.)Dark green plates

29 (MI at 200 K)

Black plates

0.07 ↔ 4 (Semi.-Semi. at 303 K)- 23 -

Crystal Structure of (MeEDO-TTF)2X (X = BF4, ClO4)
For X = BF4

Metal down to 10 K

Orthorhombic
Cmcma = 28.752(2) Å
b = 12.369(1)c = 6.969(1)V = 2478.4(4) Å3
Z=4
R = 5.7 %(Io > 2σ(Io))
GooF = 1.044

a-axis projection
2D Fermi Surface
with weak intermol. t = 11.7, p = 8.4,
interactions-3s = -5.1 × 10

c-axis projection
Donor: Head-to-Head(parallel)Anion: Disordered- 24 -

(MeEDO-TTF)2PF6: Semiconductor-Semiconductor
H-phaseNearly Localized
Charge-orderω = 0ºL-phaseω ≈ 4ºDefinitive
Charge-orderBlack Plate H-phase
isostructural withmetallic BF4 & ClO4V/t

Area of Conducting Layer (Å2)
Stable BF4 ClO4PF6Semimetal 86.19 86.41 88.07 conductor - 25 -

有機導電体における分子自由度

・格子点 ≠ 点
形状・大きさ・機能性形状変化が可能
・新たな機能性物質
多重不安定性
外場敏感相転移物質
光誘起相転移物質→ 開始時刻の制御→ 非平衡状態の研究

OS

SOSS- 26 -

低温物質科学研究センター

Research Center for Low Temperature and Materials SciencesOOSS

SShνOSOS

coolheatMetalSSInsulator

分子性材料開拓・解析研究分野
Division of Molecular Materials Science- 27 -