A new family of Pt(II) isocyanide complexes with NNC-type pincer ligands: correlation between structural features and aggregation-induced emission

Four square-planar [(NNC)Pt(CN-Xyl)]OTf complexes bearing a novel tridentate ligands (NNC-1/4) were synthesized and fully characterized. Photophysical properties of the obtained compounds were investigated in acetonitrile solution, solid state and aqueous dispersion. It was shown that the complexes in their monomeric form exhibit moderate phosphorescence in the visible and NIR regions with a clear correlation of emission maxima with the nature of the cyclometalated fragment in the pincer ligand. Complexes with substituted phenyl ring as the C-coordinated fragment (NNC-1/3)Pt(CN-Xyl) demonstrate aggregation induced emission (AIE) with a strong red shift of emission bands in the solid state and water dispersions, the magnitude of which correlates with the packing mode of the molecules, i.e., with the number of platinum metal centers taking part in formation of aggregates. The complex containing benzothienyl C-coordinated moiety (NNC-4)Pt(CN-Xyl) shows no AIE effects that is in agreement with its structural features, which do not allow formation of the aggregates with short Pt–Pt contacts. All correlations between the photophysical behavior of the complexes, their composition and structural parameters were also confirmed by quantum-chemical calculations based on the analysis of the model systems containing monomers, dimers and trimers of the starting complexes.