Inkjet printing to trap transient polymorphs described by Ostwald's rule and observed by second-order nonlinear optical imaging of chiral crystals (SONICC)
Abstract
Second-order nonlinear optical imaging of chiral crystals (SONICC) is a powerful tool for analyzing crystals of chiral molecules prepared from racemic solutions that can form both conglomerates and/or racemates. The overwhelming majority of homochiral crystals comprised of a single enantiomer are bulk-allowed for second harmonic generation (SHG), or the frequency doubling of light. Conglomerates of homochiral crystals are also generally expected to be SHG-active. In contrast, most racemates crystallize in space groups with inversion symmetry (centrosymmetric) and are symmetry-forbidden for SHG. Analysis of nanocrystals formed by inkjet printing of racemic aqueous amino acid solutions resulted in the observation of SHG-activity, despite the absence of SHG from powders formed from those same solutions upon slow drying. The emergence of SHG-active nanocrystalline forms upon rapid drying from ∼pL droplets dispensed by inkjet printing is attributed to the presence of kinetically trapped transient polymorphic states. The presence of these metastable structures provides insight into the nature of crystal nucleation and supports Ostwald's rule or polymorph ordering.
Degree
M.S.
Advisors
Simpson, Purdue University.
Subject Area
Chemistry|Optics
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