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

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 box-like and hexagon-like
shapes offer an opportunity to control the arrangement within 2D layers
where D-A inter­actions direct the superstructures. While a box-like
2,6-disubstituted naphthalene-based tetracationic cyclophane does
not form square tiling patterns, a truncated hexagon-like 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 box-like and hexagon-like cyclophanes, respectively. Co-crystallization
of the box-like 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 hexagon-like 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 electron transport.