Physical properties of a new family of charge transfer complexes and their Langmuir films

Solid State Communications, Vol. 94, No. 3, pp. 193-196, 1995 Elsevier Science Ltd Printed in Great Britain 0038- 1098/95 $9.50+.00 00381098(95)oooo!J-7

Pergamon

PHYSICALPROPERTIESOF A NJ3WFAMILY OF CHARGE TRANSFER

COMPLEXES AND THEIR LANGMUIR FILMS

Yufang XL40

(Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000) (Received 20 November 1994 by 2. Can)

Synthesis of a new family

of charge transfer complexes-tetramethylthiotetra-

thiafulvalene-C,Bm(TMT-TIF-Cam,

n=6,24)

is described. The charge transfer

in complexes is investigated by UV electronic absorption spectra, KRD technique and ESR spectroscopy. The pressure-area

isotherm shows that TM’I-TIT-C,Bm

could form the stable monolayers at the air-water interface.

Keywords:

C,

A. Mlerenes

A. thin films

is one of the most promising

B. chemical synthesis

functional

depends on the spreading solution11’~161. It arises from

materials and has led to various attention in synthesis

hydrophobicity

of new materials,

largely reduced by introduction

research.

physical properties

and

C, undergoes a one-electron

reduction

yield C, radical anionl’l and a one-electron to

the

oxidation

radical

stable

However,

reducing

it is

and

difficult

tetrathiafulvalene(.

for

C,

to

monolayers at the air-water

present

work,

properties

that C, can react

oxidizing

of hydrophilic groups,

interface and the

conductivity of this LB film reaches 10” S/~ml’~. In the

and

potentials are -0.44 Vu1 and 1.76 Vlq vs SCE

strongly

aggregation is

such as Br atoms. For example, Ce,Br, can form the

to

oxidation

cation C, l*-‘l. The reduction

respectively in CH,Cl,. It is known with

applied

of C,. The molecular

we

report

the

transfer complexes-tetramethylthio

react

C,Bm(TMT-‘ITF-Cam,

tetrathiafulvalene-

n=6,24).

Syntheses of TMT-TTF

C, derivatives, such as C,Bm,

physical

and thin films of a new family of charge

specieslz’-‘1. with

synthesis,

and C,Bm

( n=6,24)

have stronger ability to accept electrons and better the

have

film-forming

IR(KBr disk): 2987, 2918, 1530, 1400,1100, 966, 883;

TIT-C,Br,

property

than

C,lr”l. A proof is that

been described previouslylyllal~. For TMT-‘ITF,

Su(CDCl3): 2.59; M/Z 388, 373, 341, 238, 223,150,118,

has been synthesizedllO]. Therefore, C,Bm

105, 91, 76; Element Anal. for C,,H,,S,: calcd(found)

is a good candidate as electron acceptors.

c: 30.90(31.11), H:3.11(3.19).UV(CHCl,): Langmuir-Blodgett(LB) thought

technique

to be one of the most

has

338, 384. For C&r,:

been

264,

IR(KBr disk):1440, 1425, 1328,

1290, 1180, 1124, 1098, 1070,1024, 938,857,

powerful tools to

316,

812,

constructure the ultra-thin film with higher conductivity.

808,710, 685, 668, 576, 554, 527. For C,Br,,

In previous work, C, as LB film materials has been

disk):1408, 1236, 1100-1040, 932, 910, 844, 818, 801,

describedl’u.

771,741, 718, 600,540,520.

The

formation

of monolayers

of C, 191

IR(KBr

194

Vol. 94, No.3

PHYSICAL PROPERTIES OF CHARGE TRANSFER COMPLEXES To a solution of 12 mg(O.Olmmol) of C,Br, in

20 ml chloroform TMT-TTF

was added

3.9mg(O.Olmmol)

of

r

dissolved in 10 ml chloroform. The mixture

was refluxed for 5 hours. After cooling the mixture, brown-dark microcrystalline The TMT-TTF-C,Br,

precipitate was obtained.

was yielded through filtering and

washing with acetone. IR(KBr disk): 2987, 2918, 1530, 1447,1420,1324,1290,1178,1120,1063,1020,972,962, 882, 772, 709,682, 665, 524. UV(CHC1,): 266, 340,386, 470,600. Element Anal. For C&,H,,S,Br,: calcd(found) c: 52.90(52.63), H: 0.76 (0.72). 10

TMT-ITF-C,Br,

20

was synthesized in a manner

similiar to that for TMT-TTF-C,Br,.

IR(KBr

disk):

2986,2920,1540,1417,1335,1305,1065,1015,970,960, 882, 774, 695,574,522,512.

40

30

20 (degree) Figure 1. The XRD pattern of TMT-‘ITF-Cam (n=6,a and n=24,b) and TMT-TTF(c)

UV(CHCI,): 266,340, 400,

470,605. Element Anal. for C,,,H,,S,Br,: calcd.(found), complexes were a simple

C: 27.74(27.68), H: 0.396(0.401).

C,Bm, UV electronic absorption spectrum of TMT-TI’F

mixture

of TMT-TIF

and

the XRD pattern would have shown peaks

corresponding to the individual components, TMT-TTF

exhibited four bands at 264, 316,338 and 384 nm. The

and C,Bm,

electronic

that the new charge transfer complexes were formed.

bands

absorption

situated

at

spectrum 221, 270,

Compared

with the electronic

TMT-TTF

and C,,

TMT-TTF-C,Bm

of C,

showed four

340 and

460nmP”‘.

absorption

bands of

it is found that the peak of

at 6OO(or 605)nm is a new electronic

exactly at the same positions. It also shows

Figure 2 shows ESR signals of TMl-TTF-&,Bre

and

TMT-TTF. Only one ESR absorption line was observed from TMT-‘ITF

and C,Br,.

The room-temperature

absorption band, which is assigned to charge transfer

value of

band

CSOBr~21] are 17G, 2.0067(Fig.2b) and 5.58 G, 2.00255,

due to partial

charge transfer between TMT-

TTF and C,Bm.

PHP-p and the g factor of TMT-TTF

respectively.

For

TMT-TTF-C,Br,,

three

and

ESR

absorption peaks appear, the g factor and AHP-p value Figure 1 shows the X-ray diffraction of TMTITF-C,Bm

and TMT-‘ITF.

TMT-TI’F-C,Bm

The XRD pattern

of

shows reflection peaks at 28=7.52’,

are 2.011, 4.2 G, 2.0073, 8.3 G; and 2.0024, 2.5 G, respectively. If the complex was simple mixture, the new three

ESR absorption

peaks would not have been

8.10°, 9.96’, 17.100, 18.94’, 19.94’, 21.2’, 22.2’, 22.6’,

observed and the ESR absorption peak is similiar to

30.28’ for TMT-TTF-C,Br,

that of TMT-TTF

(Fig.la)

and

Ze=7.62’,

and C,Br,. It is shown that the new

13.14’, 18.98’, 19.98’, 20.56’, 22.14’, 22.66’, 23.0°, 28.52’,

charge transfer complex was formed. The new three

30.34’ for TMT-TTF-C,Br,

ESR absorption

peaks arise from the occurrence

charge transfer

between TMT-TTF

TMT-TTF

(Fig.lb). The pattern of

reveals the reflection

peaks at 28=7.56’,

and C,Br,

10.02’, 13.29’, 15.12’, 17.12’, 17.58’, 19.00, 20.04°,22.200,

interaction

22.70°, 30.40°, 32.62’, 34.50°, 35.200, 38.2’(Fig.lc).

transfer takes place between TMT-TTF

By

TMT-TTF,

entirely different in structure

voltammetry, is a good electron donor.

If the

and

of nuclei. It is possible that the charge

comparison it becomes evident that the complexes are from TMT-ITF.

of

which has been

investigated

and C,Br,. by cyclic

Vol. 94, No.3

PHYSICAL, PROPERTIES OF CHARGE TRANSFER COMPLEXES

Molecular

195

area (“In3

Figure 3. The T-A isotherm of the complexes, (a) TMT-TI’F-&,Br6,

(b) TMT-‘ITF-C,Br,

were formed at the air-water interface

and did not

collapse

area of the

until 40 mN/m. The limiting

complexes C,Br,

is found to be 1.26 nm* for TMT-TTF-

and 1.56 nm* for TMT-TTF-C,Br24.

that it is efficient to reduce the molecular

and TMT-TTF(b)

of C,Brn.

The limiting area is consistent

calculated

from the molecular

C,Bmt”I, The surface pressure-area isotherm of TMT-TTF is a nonamphiphilic

compound.

with that

crystal structure

which shows that the monolayer

formed at the air-water

of was

interface.

It could not form The transfer of thin Ehns, physical properties of LB

floating film at the air-water interface. It is seen from Fig. 3 that the stable floating

aggregation

and improve the film-forming property by introduction

Figure ‘2.The ESR absorption signals of TMT-TTFC,Br,(a)

It shows

films of the complexes

films based on these two complexes are under progress.

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