It remains a great challenge to achieve polar order in organic molecular crystals because anti-parallel alignment of side-byside molecules is intrinsically preferred. We have addressed this problem with a rational design that focuses on the polar stacking of parallel beloamphiphile monolayers (PBAMs) with strong lateral quadrupole-quadrupole attractions. We employ arene-arene interactions as lateral synthons. The first successes were achieved with unsymmetrical donor (X), acceptor (Y) substituted acetophenone azines which form polar PBAMs with double T-contacts between the azines. Near-perfect alignment was achieved with the methoxy series of (MeO, Y)-azines with Y = Cl, Br, I. Here, we report on the synthesis, the character-ization (GC/MS, 1 H NMR, 13 C NMR, FTIR), the crystallization, and the single-crystal X-ray analyses of the phenoxy series of (PhO, Y)-acetophenone azines with Y = F, Cl, Br, I. Properties of (RO, Y) azines were computed at the APFD/6-311G* level and are discussed with reference to p-nitroaniline (PNA). This (PhO, Y) series embodies an improved PBAM design based on triple Tcontacts which is shown to facilitate faster crystallization and to produce larger crystals. Perfect polar-alignment has been achieved for the phenoxy series of (PhO, Y)-azines with Y = Cl, Br, I and the (PhO, F)-azine also features near-perfect dipole alignment.
The central question of the paper concerns the CEISR effect in the case of symmetrical p-disubstituted acetophenone azines. We use intermolecular interaction inventory analyses to firmly establish the inequivalence or equivalence of the two arenes.
The differences are discussed of the antiferroelectric and ferroelectric stacking of the PBAMs of the polymorphs of (PhO, F)-azine. We will show how non-covalent interlayer H⋯F and F⋯F interactions between the PBAM surfaces affect their stacking.
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