Electrogenerated chemiluminescence from the monomer of a tetradentate chelate Pt(II) compound

Highlights: • The ECL of Pt (II) complexes with planar core structures can be switched between monomer excited states and excimers. • The bulky diphenyl amino group in the phenyl of ptrz ligand results in dominant ECL emission from the Pt complex Ptm monomer. • In the annihilation path, weak ECL signal was produced from the combination of Ptm radical anions and cations. • Dichloromethane could serve as moderate co-reactant to enhance the ECL signal of Ptm. • ECL efficiency of the Ptm/S₂O₈²⁻ coreactant system was enhanced up to 14 times of that of the Ru (bpy)₃²⁺/S₂O₈²⁻ one. Pt (II) compounds have drawn great attention due to their excellent phosphorescence properties. Interestingly, Pt (II) complexes with planar core structures have a great tendency to generate stacked dimers, leading to excimer emission in electrogenerated chemiluminescence or electrochemiluminescence (ECL) processes. It was found through this work that the excimer ECL could be adjusted to monomer excited one by introducing bulky substituents to the ligands. Here, the electrochemical and ECL properties of a tetradentate chelate Pt (II) complex (Ptm) containing an NC-chelate phenyl-1,2,3-triazolyl (ptrz) ligand and an NC-chelate pyridyl-1,2,4-triazolyl (pytrz) ligand in the central core, along with a diphenyl amino substituent in the phenyl of ptrz ligand, was investigated. Ptm showed weak ECL efficiency in the annihilation path and persulfate turned out to be a very good co-reactant to enhance dramatically the ECL intensity. Light emission mechanisms were probed by means of the spooling ECL spectroscopy. It was found that only monomer excited states were generated in the ECL process attributing to the large steric hindrance by bulky diphenyl amino substituent in the ptrz ligand. This is in contrast to ECL of some Pt complex where diphenyl amino substituent was replaced by two small size fluorine atoms leading to dominant excimer ECL emission. Those results well indicate that the ECL of Pt (II) complexes with planar core structures can be adjusted by simply increasing the steric hindrance.