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Science 30 October 1998:
Vol. 282. no. 5390, p. 841
DOI: 10.1126/science.282.5390.841a
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The second-order nonlinear optical responses of chiral molecules, such as frequency doubling, can be enhanced by supramolecular ordering. Verbiest et al. (p. 913) show that Langmuir-Blodgett films of substituted helicene molecules form helical fibers. Films of one molecular handedness are better organized and show much stronger second-order nonlinearity (by a factor of 30) than films of racemic mixtures. These helicene molecules would not normally be expected to exhibit high second-order effects, but the formation of chiral helical bundles enhanced certain components of the susceptibility tensor describing optical nonlinearity. The ability to form layers of opposite chirality will be useful for generating thicker films that maintain their nonlinear properties through quasi-phase-matching methods.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)