Crystal Engineering of Some 2,4,6-Triaryloxy-1,3,5-triazines: Octupolar Nonlinear Materials.
The principles of crystal engineering were used to design a family of structures with potential as octupolar nonlinear optical (NLO) materials. The major aim in such an exercise, a carry-over of mol. symmetry into the crystal, is possible with a retrosynthetic approach. An appropriate choice of precursor trigonal mols. leads from the concept of the dimeric Piedfort unit. The crystal structures and NLO properties of 2,4,6-triaryloxy-1,3,5-triazines, 1-6, are reported. These compds. consistently form quasi-trigonal or trigonal networks that are 2-dimensionally noncentrosym. Substitutional variations on the Ph moieties that were expected to maintain or to perturb this trigonal network were explored. Mol. nonlinearities were measured by Harmonic Light Scattering (HLS) expts. Among the compds. studied, 2,4,6-triphenoxy-1,3,5-triazine, 1 adopts a noncentrosym. crystal structure with a measurable SHG powder signal. All these crystal structures are stabilized by weak intermol. interactions such as herringbone, p...p, C-H...O, and C-H...N H bonding. These octupolar mols. are more isotropic than the classical p-nitroaniline based dipolar NLO mols., and this is advantageous from the viewpoint of potential electrooptic applications.
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