Synthesis, structure and luminescence of novel co-crystals based on bispyridyl-substituted α,β-unsaturated ketones with coformers

Based on 2,6-bis((pyridin-4-yl)methylene)cyclohexanone (A) and N-methyl-3,5-bis((pyridin-4-yl)methylene)-4-piperidone (B) with coformers, three novel macrocyclic co-crystals, (A)⋅(resorcinol) (1), (A)⋅(1,3,5-benzenetriol) (2), (B)2⋅(1,3,5-benzenetriol)2 (3) and three chain co-crystals, (A)⋅(hydroquinone) (4), (A)⋅(isophthalic acid) (5), (B)⋅(isophthalic acid) (6) have been synthesized and structurally characterized by IR, 1H NMR and X-ray crystal structure analysis. Structural analysis indicates that four-component macrocycles in 1–3 are generated from “clip-like” resorcinol templates and building blocks, while 4–6 show infinite H-bonding chains. In addition, the luminescent properties of A, B and 1–6 are investigated primarily in the solid state. Compared with free building blocks, 1–6 are blue-shifted 55–60 nm with decreasing emission intensities in spite of the enhancement in 6. The change of luminescent properties might be caused mainly by incorporation of coformers into co-crystals, including H-bonds, molecular conformations, arranging dispositions and π–π characteristics. It might have potential applications for crystal engineering to construct patentable crystals with interesting luminescent properties.