Molecular Lego (R): non-centrosymmetric alignment within interdigitating layers

Ashwell, Geoffrey J., Hamilton, Richard, Wood, Barry J., Gentle, Ian R. and Zhou, Dejian (2001) Molecular Lego (R): non-centrosymmetric alignment within interdigitating layers. Journal of Materials Chemistry, 11 12: 2966-2970. doi:10.1039/b105657n

Author Ashwell, Geoffrey J.
Hamilton, Richard
Wood, Barry J.
Gentle, Ian R.
Zhou, Dejian
Title Molecular Lego (R): non-centrosymmetric alignment within interdigitating layers
Journal name Journal of Materials Chemistry   Check publisher's open access policy
ISSN 0959-9428
Publication date 2001
Sub-type Article (original research)
DOI 10.1039/b105657n
Open Access Status Not Open Access
Volume 11
Issue 12
Start page 2966
End page 2970
Total pages 5
Place of publication Cambridge
Publisher The Royal Society of Chemistry
Collection year 2001
Language eng
Subject C1
250103 Colloid and Surface Chemistry
780103 Chemical sciences
Abstract (E)-N-Hexadecyl-4-[2-(4-octadecyloxynaphthyl) ethenyl] quinolinium bromide, which has a wide-bodied chromophore and terminal n-alkyl groups, adopts a U-shape when spread at the air-water interface but a stretched conformation when compressed to ca. 35 mN m(-1). The high-pressure phase has a narrow stability range prior to collapse but may be extended from 40 to 60 mN m(-1) by co-spreading the dye in a 1 : 1 ratio with docosanoic acid. The mixed Langmuir-Blodgett (LB) film has a monolayer thickness of 4.6 +/- 0.2 nm which decreases to 2.5 +/- 0.1 nm layer(-1) in the bulk, the reduction arising from an interdigitating layer arrangement, both top and bottom. It is the first example of LB-Lego(R) and, in addition, represents the only fully interdigitating structure with non-centrosymmetrically aligned chromophores. They are tilted 38 degrees from the substrate normal. The second-harmonic intensity increases quadratically with the number of layers, i.e. as I-(N)(2 omega) = (I(1)N2)-N-2 omega, with a second-order susceptibility of chi ((2))(zzz) = 30 pm V-1 at 1064 nm for refractive indices of n(omega) = 1.55 and n(2 omega) = 1.73, d = 2.5 nm layer(-1) and phi = 38 degrees. Angle resolved X-ray photoelectron spectra (XPS) of these films provide no evidence of the bromide counterion, which suggests that it is replaced by OH 2 or HCO3-, which occur naturally in the aqueous subphase, or C21H43COO- from the co-deposited fatty acid. This probably applies to all cationic dyes deposited by the LB technique.
Keyword Chemistry, Physical
Materials Science, Multidisciplinary
Nonlinear-optical Applications
2nd-harmonic Generation
Lb Films
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Mathematics and Physics
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Created: Tue, 14 Aug 2007, 15:38:32 EST