Solvent effects and polymorphic transformation of organic nonlinear optical crystal L-pyroglutamic acid in solution growth processes I. Solvent effects and growth morphology

Single crystals of a new promising nonlinear optical material for the tunab le UV harmonic generation, L-pyroglutamic acid 60 x 20 x 20 mm(3) in size w ere obtained from aqueous solution by using the temperature-lowering method . Solubility of L-pyroglutamic acid in different solvents was measured. The single crystals showed different morphological characteristics and growth rate in different solvents with different crystallographic orientations. Me thanol or ethanol solutions yielded needle-like crystals. In mixed solution such as methanol/H2O or ethanol/ H2O plate-like crystals with a thickness in the direction [0 1 0] were observed. The water as a good solvent, howeve r, produced long prism-like crystals. The two polymorphs of L-pyroglutamic acid (alpha and beta phases) were found for the first time. The growth shap es of alpha-phase is mainly a prism and beta phases is a rhombic plate.The growth rate of alpha and beta phases is mainly a function of the supersatur ation of the L-pyroglutamic acid in solution. (C) 1999 Elsevier Science B.V . All rights reserved.