Effects of aliphatic tails on monolayer structures of hemicyanine dyes at the air/water interface as studied by in situ SHG measurements and surface pressure-area isotherms

Langmuir monolayer assemblies of three kinds of hemicyanine (aminostyryl-pyridinium) dyes having aliphatic tail(s) at different positions of dye skeleton were studied by in situ second harmonic generation (SHG) measurements, also with surface pressure-molecular area (π-A) isotherms. The dye having a...

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Bibliographic Details
Published in:	Journal of photochemistry and photobiology. A, Chemistry. Vol. 132; no. 1; pp. 75 - 80
Main Authors:	Niidome, Yasuro, Ayukawa, Hiromitsu, Yamada, Sunao
Format:	Journal Article
Language:	English
Published:	Lausanne Elsevier B.V 20-03-2000 Elsevier Science
Subjects:	Air/water interface Chemistry Exact sciences and technology General and physical chemistry Hemicyanine Langmuir blodgett films Monolayer Second harmonic generation Surface physical chemistry Monolayer Second harmonic generation Hemicyanine Air/water interface Structure effect Organic cation Arachidic acid Chain length Air water interface Experimental study Fatty acids Amphiphilic compound Cyanine dye Interface structure Mixed monolayer Molecular orientation Langmuir Blodgett layer
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Summary:	Langmuir monolayer assemblies of three kinds of hemicyanine (aminostyryl-pyridinium) dyes having aliphatic tail(s) at different positions of dye skeleton were studied by in situ second harmonic generation (SHG) measurements, also with surface pressure-molecular area (π-A) isotherms. The dye having an aliphatic tail at the nitrogen atom of the aminostyryl moiety afforded stable condensed phases at higher surface pressures than ∼30 mN m −1, whether the layer was diluted with arachidic acid (AA) or not. In the case of the dye having an aliphatic tail at the nitrogen atom of the pyridinium moiety, stable monolayers were formed when the dye fraction was lower than 0.6. As to the dye having two aliphatic tails at the both nitrogen atoms, expanded phases were prominent when the dye fraction was larger than 0.5 and condensed phases appeared at a substantially diluted condition (0.2 dye fraction). It was suggested that the aliphatic tail bound to the amino group was favorable to form the ordered monolayer structure, while that bound to the pyridinium moiety was unfavorable to dense and robust packing. All dyes exhibit similar monolayer structures only at a substantially diluted condition (dye: AA=0.2:0.8).
ISSN:	1010-6030 1873-2666
DOI:	10.1016/S1010-6030(00)00207-0