Nonlinear susceptibility of a cyanobiphenyl derivative at the air/water interface: improved measurement of molecular orientation by optical second harmonic generation

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DOIResolve DOI: http://doi.org/10.1021/jp0541866
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TypeArticle
Journal titleThe Journal of Physical Chemistry B
ISSN15206106
Volume110
Issue2
Pages883890; # of pages: 8
AbstractThe nonlinear susceptibility tensor, χ², for second harmonic generation (SHG) by a monolayer of the cyanobiphenyl derivative 4-n-octyl-4′-cyanobiphenyl (8CB) at the air/water interface has been measured with the fundamental frequency hω=1.55eV (λ=800nm). The contribution of the water subphase was estimated by measuring the magnitudes and relative phases of the nonlinear susceptibilities of the bare and monolayercovered water surfaces. All nonzero elements of χ² are placed on an absolute scale by comparison with SHG in reflection from a z-cut quartz crystal. The experimental measurements for the 8CB monolayer are compared with computed susceptibilities derived by using standard time-dependent perturbation theory in conjunction with a semiempirical electronic structure model. Good agreement has been found between experimental and computational results when the average tilt angle of the cyanobiphenyl chromophore of 8CB is in the range 60-70° relative to the surface normal. A critique is given of an alternative, simplified measurement procedure of the tilt angle in which only the dominant element of the molecular hyperpolarizability tensor is considered. It is shown that the simplified procedure is invalid for 8CB monolayers when the tilt angle is greater than ~70°.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada; NRC Steacie Institute for Molecular Sciences
Peer reviewedNo
Identifier18077705
NPARC number12327223
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Record identifier1f4d01b4-d8f9-4653-9ee1-90dff9218fc0
Record created2009-09-10
Record modified2016-05-09
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