Naphthalimide-Modified Clusters for Red-Emitting Devices with High Color Purity

Conventional fluorescent materials frequently exhibit narrow-band emissions with a small full width at half-maximum (fwhm) due to localized-state characteristics, but electroluminescence is less efficient owing to the utilization of only singlet excitons. In this work, taking advantage of naphthalimide (NAI)-acetylide derivatives with a rigid planar structure and localized transition characteristics, we elaborately designed two mononuclear Pt(II) complexes with weak double emissions of fluorescence and phosphorescence. Taking them as synthetic precursors, we prepared three PtAu₂ heteronuclear clusters and successfully attained highly efficient narrow-band red phosphorescence with the fwhm below 30 nm. Both theoretical and experimental results suggest that the phosphorescence of PtAu₂ clusters mainly originates from the naphthalimide-localized ³IL (intraligand) triplet state. Solution-processed organic light-emitting diodes (OLEDs) achieved highly efficient narrow-band red electroluminescence with an external quantum efficiency (EQE) of 16.7%. The CIE coordinates of the electroluminescence (0.69, 0.31) closely match the standard red emission for ultrahigh-definition display.