The Role of Substituent Effects in Tuning Metallophilic Interactions and Emission Energy of Bis-4-(2-pyridyl)-1,2,3-triazolatoplatinum(II) Complexes

The photoluminescence spectra of a series of 5-substituted pyridyl-1,2,3-triazolato Pt^II homoleptic complexes show weak emission tunability (ranging from λ=397-408 nm) in dilute (10^-6 M) ethanolic solutions at the monomer level and strong tunability in concentrated solutions (10^-4 M) and thin films (ranging from λ=487-625 nm) from dimeric excited states (excimers). The results of density functional calculations (PBE0) attribute this "turn-on" sensitivity and intensity in the excimer to strong Pt-Pt metallophilic interactions and a change in the excited-state character from singlet metal-to-ligand charge transfer (¹MLCT) to singlet metal-metal-to-ligand charge transfer (¹MMLCT) emissions in agreement with lifetime measurements. Turn-on tunability: A series of bis-4-(2-pyridyl)-1,2,3-triazolatoplatinum(II) complexes display variable emission tunability. At low concentration, the emission can be tuned only slightly by changing the nature of the substituent but at higher concentrations tunability is enhanced. This "turn-on" sensitivity in the excimeric emission is attributed to strong Pt-Pt metallophilic interactions and a change in the excited-state character.