Yellow-Emitting, Pseudo-Octahedral Zinc Complexes of Benzannulated N∧N∧O Pincer-Type Ligands

A series of yellow-emitting, pseudo-octahedral Zn(II) complexes supported by monoanionic, tridentate acetylacetone-derived N boolean AND N-boolean AND O ligands incorporating phenanthridine (benzo[c]quinoline) units is presented. These species emit weakly in solution but exhibit extended millisecond luminescence lifetimes in the solid state at room temperature, and in a frozen glass at 77 K, indicative of phosphorescence from low-lying triplet excited states. Excitation spectra indicate a role for aggregation in enhancing emission in the solid state. In contrast to four-coordinate phenanthridinyl amide-supported tetradentate Zn(II) complexes which are nonemissive in fluid solution, solid-state X-ray crystallographic structures, solution IR spectroscopy, and computational analysis all indicate a delocalized character for the central deprotonated NH which tempers the amido character of the ligand. This design provides a mechanism for turning on long-lived luminescence from N-heterocycle/amido-supported Zn(II) coordination compounds.

Automated summary

This study presents a series of unique Zn(II) complexes with a pseudo-octahedral structure. By incorporating phenanthridine units into the ligands, these complexes exhibit extended luminescence lifetimes in the solid state. The research also indicates the role of aggregation in enhancing emission in solid state.