A naphthalene-based ligand, N,N,N′,N′-tetrabenzyl-naphthalene-1,5-diamine (L1) has been synthesized and crystallized as two polymorphs, α and β. There are no strong hydrogen bonding donors, instead C–H⋯π interactions play critical roles in the stabilization of the structures of the two polymorphs with different packing motifs. The ligand L1 can be doubly protonated and coordinate with the “second-sphere” of [CoCl4]2− using N–H hydrogen bond donors to form two neutral supramolecular complexes [H2L1]2+[CoCl4]2− (1) and EtOH ⊂ [H2L1]2+[CoCl4]2− (2). L1 in 1 and 2 adopts the arrangement manner of stable polymorph α. The [CoCl4]2− anions are connected with L1 through N–H⋯Cl interactions, meanwhile, the anion [CoCl4]2− acting as an “off–on” switching template controls the photoluminescence.
![Graphical abstract: Polymorphism and photoluminescence in a naphthalene-based ligand, and its supramolecular structures through second-sphere coordination with the [CoCl4]2− anion](http://hg.y866.cn/compound/lib/scimg/usr/1/C3RA22748K.jpg)
