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A Molecular Architectural Approach
to Novel Electro-Optical Materials
Malkiat S. Johal, Laura B. Smilowitz, Jeanne M. Robinson, CST-6
DeQuan Li*, CST-4
This is the final report of a three-year, Laboratory Directed Research and
Development (LDRD) project at Los Alamos National Laboratory (LANL).
The goal is to construct polar multilayers with nonlinear optical coefficients
larger than classical inorganic crystals such as KDP or quartz. The strategy
is to use various chemical interactions such as covalent bonds or hydrogen
bonding to build polar structures. We have synthesized novel barbituric acid
and melamine derivatives that will spontaneously self-assemble into a
supramolecular ribbon according to their complementary H-bond motif.
This supramolecular ribbon can then stack into a polar multilayer structure
as verified by sum frequency generation (w1+o2) or second harmonic
generation (when o, = o2). Second harmonic generation yields a value of
d33 = 3.2 pm/V for the self-assembled films and sum frequency generation
shows a net polar orientation of the methyl groups in the multilayer along
the surface normal. X-ray diffraction confirms the layered structure and
produces the periodicity of -41 A, which corresponds well to the width of
the supramolecular ribbons (-40 A).
Background and Research Objectives
Ordered molecular assemblies can lead to materials with extremely high second-
order nonlinear optical (NLO) properties.3 Although organic molecules with high
nonlinearities are well known,45 it has been difficult to design bulk materials in which the
molecules are well aligned. Generating ordered assemblies by the Langmuir-Blodgett (LB)
technique often leads to metastable films and is only possible for a narrow range of
molecular species,' while chemical synthesis of covalently bound supramolecular structures
on surfaces can be difficult and time-consuming.' The formation of polar multilayers by
drop-casting is an attractive alternative, especially if such structures lead to
thermodynamically stable asymmetric (head-to-tail) assemblies. Asymmetric assemblies are
*Principal Investigator, e-mail: email@example.com
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Li, D.; Johal, M.S.; Smilowitz, L.B. & Robinson, J.M. Molecular Architectural Approach to Novel Electro-Optical Materials, report, June 29, 1999; New Mexico. (digital.library.unt.edu/ark:/67531/metadc723360/m1/4/: accessed October 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.