Issue 4, 1998

Synthesis and non-linear optical properties of (N-alkylpyrrol-2-yl)squaraine derivatives. Part 2

Abstract

Two squaraine dyes, bis(5-ethyl-1-octadecylpyrrol-2-yl)squaraine (Et-Py) and bis(3,5-dimethyl-4-ethyl-1-octadecylpyrrol-2-yl)squaraine (MeEt-Py) have been synthesised and studied as Langmuir–Blodgett (LB) monolayers using atomic force microscopy (AFM), angle dependent X-ray photoelectron spectroscopy (ADXPS) and grazing incidence X-ray diffraction (GIXD). Additional investigations include both their linear and second-order non-linear optical properties, the latter giving deff = 1.5 ± 0.2 pm V–1 for Et-Py and 1.1 ± 0.2 pm V–1 for MeEt-Py. Comparisons with the previously reported dyes, bis(1-octadecylpyrrol-2-yl)squaraine (Py) and bis(3,5-dimethyl-1-octadecylpyrrol-2-yl)squaraine (Me-Py) reveal that Me-Py is the only one of the four which deposits as ordered, densely packed LB films which allows further studies on Me-Py so as to ascertain a valid mechanism for the occurrence of second harmonic generation (SHG) in these centrosymmetric molecules. The results presented demonstrate that the experimentally observed SHG in squaraines arises from a surface induced orientational effect where higher SHG is achieved if the squaraine head-group is essentially perpendicular to the required hydrophilic substrate.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1998, 779-784

Synthesis and non-linear optical properties of (N-alkylpyrrol-2-yl)squaraine derivatives. Part 2

D. E. Lynch, I. R. Peterson, M. Floersheimer, D. Essing, L. Chi, H. Fuchs, N. J. Calos, B. Wood, C. H. L. Kennard and G. John Langley, J. Chem. Soc., Perkin Trans. 2, 1998, 779 DOI: 10.1039/A708892B

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