Fabrication and properties of self-assembled films of poly(thiophene) derivatives

ELSEVIER

Synthetic Metals 101 (1999) 132-133

Fabrication

and Properties

of Self-Assembled

Films of Poly(thiophene)

N. Sato a , M. Rikuknwa “b, KSanui ‘Deparrmnr

Abstract We fabricated

Derivatives

“b, N. Ogata a

Chemistry, Sophia Universiry, 7-I Kioi-Cho, Chiyoda-ku, Tokyo 1023554, bCREST, Japan Science and Technology Corporarion (JST)

of

electrostatic

self-assembled

thin films

with poly(thiophene-3-acetic

Japan

acid) (PTAA)

as a polyanion

and a

positively-charged second-or&r NLG chromophore as a cation. W-Vi& FT-IR, and second-harmonic generation (SHG) were measuredin order to investigate the process of anion and cation adsorption and to understand the relationship between stnrture and optical properties of the ultra thin films. UV-Vis and Fl-IR spectra of these films indicated that PTA.4 and the-NW chromophdre

formed

centrosymmetricaliy

a layer-by-layer aligned within

h’ey H’ o rds : Self-assembly, Introduction Self-assembled

str~ture.

SHG measurements

suggested

that the NLO chromophores

Polythiophene

derivatives,

Non-linear

optical methods H&

thin

films

are attracting

a great deal of

these techniques are useful for fabricating effective non linear optical (NLO) materials. Second-order NLG effects are created when chromophores are ways.

have been made to design NLOfilms. Blodgett techniques, liquid crystals,

Various

attempts

They inclti Langmuirpoled polymers in an

CH:, v

OH

attention for possible applications on opto-electronic devices. Fabrication of thin films using self-assembly systems enables u to control molecular structure on thenano-scale. Especially,

arranged in non-centrosymmetric

were non-

the self-assembled films.

4

Scheme 1 Structures Experimental hlaterials preparedby

of PTAA and DSMP.

Poly(thiophene-3-acetic the oxidativepolymerizaiion

3-acetate (Lancaster Synthesis)

acid) (PTAA) was of ethyl thiophene-

with ferric chloride,

followed

electric field, and self-assembly techniques. Construction of NZO superlattices by self-assembling via covaient linking has

by acid hydrolysis of the ester group[5]. The chromophore, 4-(4-dimethylamino)styryl-l-methylpyridine

been

(Aldrich,

recently

adsorption

reported

[l],

and

has been successfully

electrostatic

applied

contain an NLG chromophore [ 2,3,4]. In this study, we demonstrate a new approach polymer

thin

films

We constructed electrostatic

with

second-order

alternate

optical properties

that

to fabricate

NLG chromophores.

DSMP) was used without further purification.

One mM PTAA solution were prepared by dissolving PTAA in 1 mM sodium hydroxide and subsequently converting the salt solution

to an acidic solution

by adding

HCl.

1 mM

and a

DSMP solutions were made by dissolving DSMP in HO. Substrate Preparation Glass slides with positively charged surfaces were used as substrates for the adsorption

NLC chromophore as a cation of adsorption, structure, and

process. Positively charged surfaces were made by treating hydrophilic substrates with (N-2-amino-ethyl-3-aino-

self-assembled

multilayer

adsorption

positively-chargedsecond-order and investigated the process

alternate

to polyions

NLO

of

of the self-assembled

structures

a polyanion

film.

by

propyl)trimethoxysilane

0379-677919915 - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)01398-8

(TMS) solutions,

M. Rikukawa

Xiultilager by

Deposition

alternately

containing typically

Multilayer

dipping

glass

the polycations

et al. / Synthetic

Metals

101

(1999)

133

132-133

films were fabricated

substrates

or anions.

in

solutions

The substrates

were

dipped for 30 min,

remove residual compounds,

washed with purified water to and dried with a nitrogen stream.

Measurements W-Vis absorption mcasurments were carriedout to monitor the layer-by-layer &position process of the optically active material in this system. The second-order NLG properties of the self-assembled were investigated

by the second harmonic

generation

technique at 1064 nm with a Q-switched

NdYAG

FT-IR spectra of a self-assembled

PTAA /DSMP

ZnSe substrate were measured with a MAGNA-IR The thickness

of the multilayer

film

film on a

750 (Nicolet). with a

Dektak 2000 profilometer. Results

Figure 1 shows the layer at 400 nm and 470 nm (La

of PTAA and DSMP, respectively) for a self-assembled P’TAA/D%MP film. As can be seen in Figure lA, the of PTAA

amount of PTAAdepositedper other hand, Figure IB exhibits indicating

that DSMP

is linear,

indicating

that the

bilayer is reproducible. aperiodic

molecules

On the increase and decrease,

on the film

desorbed into the aqueous PTAA solution were immersedinto

are partly

when the substrates

the PTAA solution.

In spite of the partial release of DSiMP molecules from the film, DSMP molecules are reproducibly deposited on the self-assembled films by immersion

Figure 2

IT-IR spectra of a self-assembled ZnSe substrate components. profilometer

indicated

that

PTAA/DSMP the film

film onto a

contained

both

Thickness of this film determined by was 28 .&bilayer. These data agreed with IT’-IR

Xonlinear

Fabrication of Multilayers number dependence of absorbance

process

20 30 40 50 60 Incident angle i degree Angular dependence of the transmitted SH signal from a self-assembled PTAhlDSklP film.

results.

and Discussion

deposition

10

(SHG)

laser.

film was determined

0

into the DSMP solution.

that PTAA and DSMP can construct electrostatic self-assembly.

These results multilayer

suggest

structtxes

by

Optical Properties Figure 2 presents the transmitted p-polarized SHG for both the p- and s-polarized fundamentals at 1064 nm for a self-assembled PT..U/DSMP film (50 layers).

The interference fringes of the SH intensity arise from the interaction of the second-harmonic waves from self-assembled films on both sides of the glass substrate. The nearly complete destructive interference assembled films

indicates that the self-

sides of the substrate

have well-

defied layer structure and SHG activities. Conclusion We have demonstrated

that PTA4 and DSMP form uniform

self-assembled multilayers. that these self-assembled centrosymmetric

alignment

The SHG measurement multilayer films and NLO activities.

indicated

have

a non-

Acknowledgments This

0.15

on both

work has been supported

Evolutional

by the Core Research for

Science and Technology

Science and Technology

Corporation

(CREST) of the Japan (JST).

Reference [l]A.K.Kakkar,

S.Yitzchaik,

T.J.Marks,

W.Lin, G.K.Wong,

[?I Y.Lvov, S.Yemsda, (1997) 107. 0.05 0

[3] X.Wang, 0

10 20 30 Layer number Figure 1 Layer number dependence of absorbance at 400 nm (A) and 470 nm (B) for a selfassembled PTA.4 / DS;ClI’ film.

S.Roscoe, F.Kubota, Langmuir,

T.Kunitake,

S.Balasubramanian,

Thin

LLi,

D.S.Allan,

9 (1993) 355. Solid Films.,

X.Jiang,

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D.J. Sandman,

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