Friday, July 20, 2012

Synthesis of Chiral Zinc Metallacrowns for Applications in Second Generation Harmonics

Here's a copy of the abstract I just submitted for the research symposium that will occur at the University of Notre Dame two weeks from today. Now I need to create my poster!

       Second harmonic generation (SHG) occurs when two photons of a specific energy are combined to form a new photon with twice the energy. Applications in opto-electronics and photonics that utilize SHG properties have traditionally been implemented in simple inorganic crystals such as potassium dihydrogenphosphate (KDP) most effectively. Recently, organic chromophores have exhibited higher and faster nonlinearities compared to inorganic crystals. The SHG properties of organic chromophores can be custom-tailored for a desired application because of the versatility of organic synthesis. Metallacrowns are inorganic analogues of crown ethers that assemble from hydroxamic acids and metals. By incorporating three or more metals into a dense ring structure, metallacrowns often exhibit unique single-molecule magnetism and luminescence properties. Metallacrowns can be used in conjunction with organic chromophores to develop novel SHG material. Engineering a crystalline material that exploits the SHG capabilities of organic chromophores has three main requirements: the crystalline structure must be non-centrosymmetric, it must arrange the chromophores such that their dipole moments are aligned parallel, and the material should be colorless so it will not absorb the frequency doubled light in the visible region. Chiral metallacrowns have been shown to form cavities that sequester and properly align organic chromophores in a non-centrosymmetric environment. Previously, a Ln(III)[15-metallacrownCu(II), pheHA-5] complex with the SHG chromophore isonicotinate exhibited modest SHG behavior. The intensity was much weaker than KDP, presumably because the crystalline blue powder absorbed much of the generated green light. Performance is likely to be increased by forming chiral metallacrowns containing zinc, which will be colorless in the visible region. This project aims to develop new chiral 12-metallacrown-4 zinc complexes using the hydroxamic acids (s)--phenylalanine and (s)--homophenylalanine. Electrospray mass spectrometry has shown that the metallacrown [12-MC-Zn(II), -pheHA-4] readily assembles in a variety of solvents. Colorless crystals of this metallacrown have been grown by diffusing a solution of pyradine with ethyl acetate. Efforts to isolate this material, optimization of the ligand synthesis, and metallacrowns with SHG chromophores for the development of SHG materials will be discussed.

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