Red to near-infrared phosphorescent Ir(iii) complexes with electron-rich chelating ligands

The design of molecular phosphors with near-unity photoluminescence quantum yields in the low-energy regions of the spectrum, red to near-infrared, is a long-standing challenge. Because of the energy gap law and the quantum mechanical dependence of radiative decay rate on the excited-state energy, compounds which luminesce in this region of the spectrum typically suffer from low quantum yields. In this article, we highlight our group's advances in the design of top-performing cyclometalated iridium complexes which phosphoresce in red to near-infrared regions. The compounds we have introduced in this body of work have the general formula Ir((CN)-N-boolean AND)(2)((LX)-X-boolean AND), where (CN)-N-boolean AND is a cyclometalating ligand that controls the photoluminescence color and (LX)-X-boolean AND is a monoanionic chelating ancillary ligand. The Ir((CN)-N-boolean AND)(2)((LX)-X-boolean AND) structure type is among the most widely studied and technologically successful classes of molecular phosphors, particularly when (LX)-X-boolean AND = acetylacetonate (acac). In our work we have pioneered the use of electron-rich, nitrogen containing ancillary ((LX)-X-boolean AND) ligands as a means of controlling the excited-state dynamics and optimizing them to give record-breaking phosphorescence quantum yields. This paper progresses through our work in three distinct regions of the spectrum - red, deep-red, and near-infrared - and summarizes the many insights we have gained on the relationships between molecular structure, frontier orbital energies, and excited-state dynamics.

Automated summary

This article discusses advances in the design of molecular phosphors that phosphoresce in the red to near-infrared regions, focusing on cyclometalated iridium complexes. The introduction of electron-rich, nitrogen-containing ancillary ligands has allowed for record-breaking phosphorescence quantum yields. The study covers insights gained on the relationships between molecular structure, frontier orbital energies, and excited-state dynamics across three distinct regions of the spectrum.