Combining Intra- and Intermolecular Charge Transfer with Polycationic Cyclophanes To Design 2D Tessellations

Abstract

A series of donor-acceptor (D–A) naphthalene–viologen-based cyclophanes of different shapes, sizes and symmetries have been synthesized and characterized. Solution optical studies on these cyclophanes reveal the existence of photoinduced intramolecular charge transfer (CT) at 465 nm from naphthalene (D) to viologen (A) units, resulting in a conformational change in the viologen units and the emergence of an emission at 540 nm. The D–A cyclophanes with boxlike and hexagonlike shapes offer an opportunity to control the arrangement into 2D layers where D–A interactions direct the superstructures. While a boxlike 2,6-disubstituted naphthalene-based tetracationic cyclophane does not form square tiling patterns, a truncated hexagonlike congener self-assembles to form a hexagonal superstructure which, in turn, adopts a hexagonal-tiling pattern. Tessellation of the more rigid and highly symmetrical 2,7-disubstituted naphthalene-based cyclophanes leads to the formation of 2D square- and honeycomb-tiling patterns with the boxlike and hexagonlike cyclophanes, respectively. Co-crystallization of the boxlike cyclophanes with tetrathiafulvalene (TTF) results in the formation of D–A CT interactions between TTF and viologen units, leading to tubular superstructures. Co-crystallization of the hexagonlike cyclophane with TTF generates well-ordered and uniform tubular superstructures in which the TTF–viologen CT interactions and naphthalene–naphthalene [π⋯π] interactions propagate with 2D topology. In the solid-state, the TTF–cyclophane co-crystals are paramagnetic and display dual intra- and intermolecular CT behavior at ~470 and ~1000 nm, respectively, offering multi-responsive materials with potential pathways for the electron transport.