Dicationic Diimine Pt(II) Bis(N-heterocyclic allenylidene) Complexes: Extended Pt center dot center dot center dot Pt Chains, NIR Phosphorescence, and Chromonics

Although square-planar Pt(II) complexes are well-known to self-assemble into supramolecules via noncovalent intermolecular Pt center dot center dot center dot Pt and/ or N-N interactions, the self-assembly of dicationic Pt(II) complexes was scarce due to the electrostatic repulsive force. Herein, a series of dicationic diimine bis(N-heterocyclic allenylidene) Pt(II) complexes were synthesized and characterized. Close Pt center dot center dot center dot Pt and/or N-N contacts are observed in the crystals of these complexes. In particular, complexes 1 center dot 2PF6 and 2 center dot 2PF6 exhibit one-dimensional packing with extended Pt center dot center dot center dot Pt contacts of 3.302 and 3.240 angstrom, respectively. The photophysical properties of these complexes in the solution and solid state were investigated. NIR emission was recorded for complexes 1 center dot 2PF6 (Amax = 950 nm) and 2 center dot 2PF6 (Amax = 855 nm) in the solid state at 298 K. To explore the aggregate behaviors of these complexes, the counteranion PF6- was exchanged to the large lipophilic anion 2,3,4tris(dodecyloxy)benzene sulfonate (LA-) and the hydrophilic anion Cl-. Complexes 1 center dot 2LA and 2 center dot 2LA or 1 center dot 2Cl and 2 center dot 2Cl could self-assemble with Pt center dot center dot center dot Pt and/or N-N interactions in the nonpolar or aqueous solutions as well. Further increasing the concentration of 1 center dot 2Cl and 2 center dot 2Cl in aqueous solution, chromonic mesophases with NIR emission (Amax = 988 nm) were obtained. DFT and TDDFT calculations were performed to gain deep insight into the dication-dication packings and photophysical properties of the complexes. The a-donating as well as N-accepting character of the N-heterocyclic allenylidene ligand endows complexes with rigid and electron-delocalized coplanar features, which are conducive to achieving the self-assembling processes associated with Pt center dot center dot center dot Pt and/or N-N interactions.