Conducting Langmuir-Blodgett films based on semiamphiphilic tetracyanoquinodimethane salts: mechanism of the homodoping process

O. Fichet, B. Agricole, H. Kassi, B. Desbat, V. Gionis, Roger Leblanc, C. Garrigou-Lagrange, P. Delhaes

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The homodoping process is a new approach to obtain a conducting Langmuir-Blodgett (LB) film in which a valence system is realized thanks to a controlled ratio between ionic and neutral compounds. In order to generalize this technique and to understand its formation mechanism we carried out a series of experiments with 3-methylthio, 4-5bis (octadecylthio) dithiolium salts with different anions (X = I-, TCNQ-, TCNQF4- where TCNQ denotes tetracyanoquinodimethane). The LB films were obtained from a Langmuir monolayer containing one of these salts and the neutral molecule C18TCNQ. Two series of experiments were performed and analysed through IR spectroscopy techniques, as follows. (i) Starting from a mixture of 1-2 dithiolium-X:C18TCNQ (1:2) we showed that the LB films obtained are independent of the anion used. As revealed by the IR absorption spectra which show both charge transfer band and TCNQ-type vibronic modes, the same final material is obtained. A chemical reaction at the gas-water interface giving rise to a mixed-valence cluster such as (C18TCNQ)2- has to be assumed. (ii) Using a special in situ IR technique, polarization modulation Fourier transform IR spectroscopy on surfaces, we carried out a comparative series of experiments on pure H2O and D2O as subphases. These in situ spectra, obtained at different surface pressures, allow us to demonstrate that the mixed-valence clusters are spontaneously formed on the water surface through the presence of vibronic modes attributed to (C18TCNQ)2 dimers. We therefore conclude that a specific redox process is occurring at the gas-water interface to give rise to these conducting monolayers.

Original languageEnglish
Pages (from-to)592-595
Number of pages4
JournalThin Solid Films
Volume243
Issue number1-2
DOIs
StatePublished - May 1 1994
Externally publishedYes

Fingerprint

Langmuir Blodgett films
Langmuir-Blodgett films
Salts
salts
valence
conduction
Infrared spectroscopy
Monolayers
Negative ions
anions
Anions
Water
polarization modulation
monomolecular films
Gases
Experiments
surface water
gases
Dimers
water

ASJC Scopus subject areas

  • Surfaces, Coatings and Films
  • Condensed Matter Physics
  • Surfaces and Interfaces

Cite this

Conducting Langmuir-Blodgett films based on semiamphiphilic tetracyanoquinodimethane salts : mechanism of the homodoping process. / Fichet, O.; Agricole, B.; Kassi, H.; Desbat, B.; Gionis, V.; Leblanc, Roger; Garrigou-Lagrange, C.; Delhaes, P.

In: Thin Solid Films, Vol. 243, No. 1-2, 01.05.1994, p. 592-595.

Research output: Contribution to journalArticle

Fichet, O, Agricole, B, Kassi, H, Desbat, B, Gionis, V, Leblanc, R, Garrigou-Lagrange, C & Delhaes, P 1994, 'Conducting Langmuir-Blodgett films based on semiamphiphilic tetracyanoquinodimethane salts: mechanism of the homodoping process', Thin Solid Films, vol. 243, no. 1-2, pp. 592-595. https://doi.org/10.1016/0040-6090(93)04188-X
Fichet, O. ; Agricole, B. ; Kassi, H. ; Desbat, B. ; Gionis, V. ; Leblanc, Roger ; Garrigou-Lagrange, C. ; Delhaes, P. / Conducting Langmuir-Blodgett films based on semiamphiphilic tetracyanoquinodimethane salts : mechanism of the homodoping process. In: Thin Solid Films. 1994 ; Vol. 243, No. 1-2. pp. 592-595.
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AU - Kassi, H.

AU - Desbat, B.

AU - Gionis, V.

AU - Leblanc, Roger

AU - Garrigou-Lagrange, C.

AU - Delhaes, P.

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AB - The homodoping process is a new approach to obtain a conducting Langmuir-Blodgett (LB) film in which a valence system is realized thanks to a controlled ratio between ionic and neutral compounds. In order to generalize this technique and to understand its formation mechanism we carried out a series of experiments with 3-methylthio, 4-5bis (octadecylthio) dithiolium salts with different anions (X = I-, TCNQ-, TCNQF4- where TCNQ denotes tetracyanoquinodimethane). The LB films were obtained from a Langmuir monolayer containing one of these salts and the neutral molecule C18TCNQ. Two series of experiments were performed and analysed through IR spectroscopy techniques, as follows. (i) Starting from a mixture of 1-2 dithiolium-X:C18TCNQ (1:2) we showed that the LB films obtained are independent of the anion used. As revealed by the IR absorption spectra which show both charge transfer band and TCNQ-type vibronic modes, the same final material is obtained. A chemical reaction at the gas-water interface giving rise to a mixed-valence cluster such as (C18TCNQ)2- has to be assumed. (ii) Using a special in situ IR technique, polarization modulation Fourier transform IR spectroscopy on surfaces, we carried out a comparative series of experiments on pure H2O and D2O as subphases. These in situ spectra, obtained at different surface pressures, allow us to demonstrate that the mixed-valence clusters are spontaneously formed on the water surface through the presence of vibronic modes attributed to (C18TCNQ)2 dimers. We therefore conclude that a specific redox process is occurring at the gas-water interface to give rise to these conducting monolayers.

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