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A Discrete Platinum(II) Metallacycle Harvesting Triplet Excitons for Solution‐Processed Deep‐Red Organic Light‐Emitting Diodes

Platinum(II) coordination‐driven architectures have exhibited unique features in fabricating functional supramolecular materials. By introducing luminescent moieties into the ligand structure, various light‐emitting metallacycles and metallacages have been facilely prepared, presenting specific applications in chemical sensing, light‐harvesting, and bio‐imaging. Except for building up the metal–ligand bonds, the platinum(II) center should also benefit the ultimate luminescence due to its unique photophysical traits. Here, a platinum(II) metallacycle with deep‐red emission for solution‐processed organic light‐emitting diodes is reported. This metallacycle is assembled by mixing a 180° di‐Pt(II) acceptor with a pyridyl‐decorated ligand functionalized by a deep‐red fluorescent emitter. Notably, the platinum(II) acceptor permits the efficient intramolecular transfer of all electrically generated singlet and triplet excitons from itself to the fluorescent moiety, which dramatically enhances the external quantum efficiency of the device compared with the one consisting of the sole ligand. The present results reveal the function of platinum(II) metallacycles in light‐emitting devices, a finding which should apply to other coordination‐driven architectures with versatile properties.