Nonsymmetric [Pt(C^NN′^C′)] Complexes: Aggregation‐Induced Emission in the Solid State and in Nanoparticles Tuned by Ligand Structure

Five square‐planar [Pt(C^N*N′^C′)] complexes (Pt1–Pt5) with novel nonsymmetric tetradentate ligands (L1–L5) were synthesized and characterized. Varying the structure of the metalating aromatic systems result in substantial changes in photophysical properties and intermolecular interaction mode of the complexes in solution and in solid state. The complexes are strongly emissive in tetrahydrofuran solution, with the band maxima ranging from 560 to 690 nm. Three of these complexes (Pt1, Pt2, Pt4) afford nanospecies upon injection of their solution into water, which show aggregation‐induced emission (AIE) with a strong red shift of emission bands. In the solid state, crystalline samples of these complexes demonstrate mechanochromism upon grinding with a bathochromic shift of the emission. DFT and TD‐DFT computational analysis of monomeric Pt1–Pt5 in solution and model dimeric emitters formed through intermolecular interaction of Pt1, Pt2, Pt4 molecules allowed assignment of observed AIE to the 3MMLCT excited states of Pt‐Pt bonded aggregates of these complexes. Square‐planar PtII complexes with tetradentate nonsymmetric {C^N*N′^C′} ligands display aggregation‐induced emission (AIE) in the solid state and in nanoparticles formed upon mixing of their solutions in THF with water. The ability of the complexes to show AIE is determined by the steric and electronic properties of the ligands’ aromatic systems.