Achieving phthalide-based fluorescent materials with hybridized local and charge-transfer characteristics for efficient deep blue OLEDs

The development of high-efficiency blue organic light-emitting materials is of significant importance for future illumination and display applications. In this work, three blue emitters, PPT, PPPT and PAPT with D-A/D-pi-A architectures have been developed, in which phthalide was first adopted as a functional acceptor. As revealed by theoretical calculations and photophysical experiments, PPT, PPPT and PAPT all display a certain degree of orbital overlap of the local excited state and exhibit typical hybridized local and charge-transfer (HLCT) characteristics. The multiple supramolecular interactions induced by phthalides endow them with high PLQYs. PAPT with the pi bridge of anthracene exerts the advantages of the LE-dominated HLCT excited state and high-lying reverse intersystem crossing (hRISC) via a hot exciton channel to obtain the highest PLQY and external quantum efficiency (EQE). As a result, the PAPT-based non-doped device achieved the maximum EQE of 7.5% at a high luminance of 1800 cd m-2. Particularly, the doped device based on PAPT exhibited superior performance with the maximum EQE of 10.2% and CIE coordinates of (0.151, 0.085), and the full width at half maximum (FWHM) was determined to be only 53 nm. The results offer a simple and efficient approach for engineering D-A/D-pi-A type HLCT materials to achieve high-efficiency deep blue OLEDs. Three blue emitters, PPT, PPPT and PAPT with D-A/D-pi-A architectures have been developed, in which phthalide was first adopted as a functional acceptor. The device based on PAPT exhibited maximum EQE of 10.2% and FWHM of 53 nm.