Photoluminescence of a Platinum(II) Complex Containing Multiresonance B–N Motif in the Cyclometalated Ligand

N- and B-Embedded polycyclic aromatic hydrocarbons with a multiresonance (MR) character have fascinating photophysical properties including high photoluminescence quantum yields and ultrapure emission color purity. The combination of MR character and heavy metal atom for developing photoluminescent transition metal complexes is of great interest but has rarely been investigated. Herein a platinum(II) complex, namely, Pt(BICPy)(acac), containing a MR moiety in the cyclometalated ligand has been synthesized and characterized. The complex displays strong narrowband phosphorescence with a quantum yield of 53% and a lifetime of 26 μs. Theoretical calculations unveiled the enhanced spin–orbit coupling effect induced by metal coordination. This work provides a way for harvesting the triplet excitons of MR type molecules.