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 (MMLCT)-M-3 excited states of Pt-Pt bonded aggregates of these complexes.

Automated summary

Five square-planar [Pt(C^N*N 'C ')] complexes with novel nonsymmetric tetradentate ligands were synthesized and characterized, showing substantial changes in photophysical properties and intermolecular interaction mode in solution and in solid state by varying the structure of the metalating aromatic systems. Some of these complexes exhibited aggregation-induced emission phenomenon in water and mechanochromism in the solid state, which were attributed to the excited states of Pt-Pt bonded aggregates of the complexes.