Naphthalimide-Modified\nClusters for Red-Emitting Devices\nwith High Color Purity

Conventional fluorescent materials frequently exhibit\nnarrow-band\nemissions with a small full width at half-maximum (fwhm) due to localized-state\ncharacteristics, but electroluminescence is less efficient owing to\nthe utilization of only singlet excitons. In this work, taking advantage\nof naphthalimide (NAI)-acetylide derivatives with a rigid planar structure\nand localized transition characteristics, we elaborately designed\ntwo mononuclear Pt(II) complexes with weak double emissions of fluorescence\nand phosphorescence. Taking them as synthetic precursors, we prepared\nthree PtAu<sub>2</sub> heteronuclear clusters and successfully attained\nhighly efficient narrow-band red phosphorescence with the fwhm below\n30 nm. Both theoretical and experimental results suggest that the\nphosphorescence of PtAu<sub>2</sub> clusters mainly originates from\nthe naphthalimide-localized <sup>3</sup>IL (intraligand) triplet state.\nSolution-processed organic light-emitting diodes (OLEDs) achieved\nhighly efficient narrow-band red electroluminescence with an external\nquantum efficiency (EQE) of 16.7%. The CIE coordinates of the electroluminescence\n(0.69, 0.31) closely match the standard red emission for ultrahigh-definition\ndisplay.