Noncentrosymmetric organic crystals of barbiturates as potential nonlinear optical phores: experimental and theoretical analyses

Abstract

This paper details with design, synthesis, isolation, spectroscopic and structural elucidation of seven crystals of organic barbiturates (a red phase of bis(5-(hydroxyimino)pyrimidine-2,4,6(1H,3H,5H)-trione) 4H-1,2,4-triazol-4-amine co-crystal (1y), 2-methylamino-1-phenyl-propan-1-ol 2-thioxo-dihydro-pyrimidine-4,6-dione (2), 4-phenylpyridine thiobarbituric acid co-crystal (3), new monoclinic polymorph of violuric acid monohydrate (4), 2-pyrrolidin-1-yl-ethylammonium bis(violurate) dihydrate (5) and redetermination of barbituric acid dihydrate (6) and noncentrosymmetric orthorhombic violuric acid monohydrate (7)). The noncentrosymmetric crystals (1r) (2) and (7) can efficiently be employed in the field of nonlinear optical (NLO) materials research. We aim at studying relationship between molecular, respectively, crystal structure and NLO properties within a relatively large range of temperatures (T = 273–500 K). The single crystal X-ray diffraction, electronic absorption, conventional and linear polarized infrared spectroscopies have been used to provide experimental structural and spectroscopic data. The deuterated derivatives of (4) and (7) have been analysed, as well. The theoretical description of linear and NLO properties of crystals (1)–(7) is based on quantum chemical ab initio methods and density functional theory (DFT). The work contributes, importantly, to the fields of nonlinear optics, crystal engineering or materials research, reflecting in mind frequency conversion of lasers, electro-optics, modulators, waveguides and more.