Crystal Structure and Theoretical Investigation of Thiobarbituric Acid Derivatives as Nonlinear Optical (NLO) Materials

Abstract

Here we report on the crystal structure of three enamine/imine TBA derivatives (1–3). Since the derivatives can take the form of enamine or imine tautomers, theoretical calculations were made to confirm that the former predominates due to higher stability (thermodynamic calculations). The enamines’ form was further corroborated by high activation energy (ΔG≠; which is >60 kcal/mol in all the cases), thus requiring a large amount of energy to pass the barrier (kinetics calculations). Furthermore, 1–3 were found to show high static hyperpolarizability (βtot), thereby making them potential candidates as nonlinear materials for electro-optical devices and crystal engineering.

Salts of barbituric and 2-thiobarbituric acids with imidazole: polymorphism, supramolecular structure, thermal stability and water solubility

“…2 Secondly, barbituric acids have the properties of potential hydrogen bond acceptors and donors, exist in various ionic or tautomeric forms, polymorphs and also demonstrate the ability to implement C-H-p-and p-p-interactions. 1 These features determine the rich diversity of the molecular and supramolecular structures of compounds and define their application in the design of pharmaceutical cocrystals, 3 catalysis, 4 molecular recognition [5][6][7] and to create magnetic, 8,9 luminescent 10 and non-linear optical [11][12][13][14][15]…”