Crystal structure, spectroscopic studies and theoretical studies of thiobarbituric acid derivatives: understanding the hydrogen-bonding patterns

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

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.