A new approach to second-order nonlinear optical (NLO) materials is reported, in which chirality and supramolecular organization play key roles. Langmuir-Blodgett films of a chiral helicene are composed of supramolecular arrays of the molecules. The chiral supramolecular organization makes the second-order NLO susceptibility about 30 times larger for the nonracemic material than for the racemic material with the same chemical structure. The susceptibility of the nonracemic films is a respectable 50 picometers per volt, even though the helicene structure lacks features commonly associated with high nonlinearity. Susceptibility components that are allowed only by chirality dominate the second-order NLO response.

No abstract

Heterohelicene 10 is synthesized in six steps from 3,3'-bithienyl. Because the number of steps is small, because the yield is 95% in the last (the reaction of a bis-enol ether with 1,4-benzoquinone-a six-step one pot procedure that constructs the helicene skeleton), and because chromatography is not required to purify any of the products in the synthesis, significant amounts are easily prepared. To convert 10 into enantiopure 3, a helicenebisquinone surrounded by four dodecyloxy groups, requires only a precedented three-step sequence. Enantiopure helicene 3, either without solvent or in dodecane (but not in chloroform) aggregates into columnar structures whose optical properties differ markedly from those of the monomer but resemble those shown previously only by aggregates of 1. Evidence of aggregation in the pure material includes optical microscopic observation of long fibrous structures and X-ray diffraction and combined transmission electron microscopic and electron diffraction analyses showing the molecules within the fibers to be organized in columnar arrays. The circular dichroism spectra, specific rotations, and fluorescent emission spectra of the aggregated structures are all distinctive, and, as reported elsewhere, the second harmonic response is very large. The linear polarizations of the monomers' and aggregates' fluorescent emissions differ greatly. The circular polarization of the aggregates' fluorescent emission, after excitation by unpolarized light, is large.

No abstract

This compound was characterized by the expected spectroscopic features and gave satisfactory elemental analyses. It is possible that the actual phosphorylating agent is complexed with dioxane; at present we are unable to distinguish between such a complex and solvated metaphosphate.Visiting Fulbright Scholar on leave from the University of Valencia, Vaiencia. Spain.

Molecules in which the cores of copper and nickel octaazaphthalocyanines are fused to four nonracemic [7]helicenes are constructed. CD and UV−vis absorption spectroscopy show that these compounds aggregate when dissolved in 75% EtOH−25% CHCl3, but not in 60% EtOH−40% CHCl3. The UV−vis absorption spectra of films of the nickel phthalocyanine are similar to those of solutions of the aggregated molecules, suggesting that the structures of the aggregates in the neat samples and in solution are similar. A calculation based on molecular mechanics shows that the energy is minimized when the molecules stack in a chiral superstructure with a core-to-core distance of ca. 3.4 Å. Atomic Force Microscopic images are in accord with this structure if on the surface of mica the stacks are isolated and perpendicular to the surface. In Langmuir films, the molecules stack in the opposite way, with the stacking axis parallel to the water. Although the molecules are remarkably symmetrical, their Langmuir−Blodgett films give very large second-order nonlinear optical responses, dominated by the ca. 21 pm/V components of the susceptibility tensors that are allowed only because the materials are chiral.

No abstract

No abstract