C₂-symmetric bis(amide) molecules: solid-state assembly, thermal stability, and second harmonic generation

Abstract

Chiral C₂-symmetric bis(amide) molecules, N,N'-bis(4-fluorobenzoyl)-(1R,2R)-diaminocyclohexane (BFBDC), N,N'-bis(4-nitrobenzoyl)-(1R,2R)-diaminocyclohexane (BNBDC), N,N'-bis(4-methoxybenzoyl)-(1R,2R)-diaminocyclohexane (BMBDC), and N,N'-bis(4-aminobenzoyl)-(1R,2R)-diaminocyclohexane (BABDC) are synthesized, and their assembly patterns in the solid state are investigated through single-crystal X-ray analysis. A range of noncovalent interactions give rise to helical superstructures in the crystals. The compounds exhibit good optical transparency and high thermal stability; these may be attributed to the specific molecular structure and extended supramolecular interactions. BMBDC and BABDC molecules possess the largest hyperpolarizabilities in the series owing to the presence of electron-donating groups and exhibit second harmonic generation (SHG) in the solid state. The optical transparency, thermal stability, and SHG capability make these materials potentially interesting candidates for quadratic nonlinear optical applications.