Solution-processable thermally activated delayed fluorescence red emitters poly(carbazole-fluorene) containing naphthalene imide units

In recent years, the development of solution-processable red-emitting TADF materials has progressed slowly compared to green and blue TADF materials in terms of device efficiency and color purity. This study reports a series of solution-processable red-emitting TADF polymers PCzF-mCP-PXZNAI-X (X = 5, 15, 25, 35), which are designed and synthesized by connecting TADF units (6-(10H-phenoxazin-10-yl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2H)-dione, PXZNAI) and host units (1,3-bis(N-carbazolyl)benzene, mCP) to the pre-obtained backbone poly(carbazole-fluorene) (PCzF-N3) through the “click” reaction. All the target TADF polymers exhibited good solubility and high thermal stability. Spin-coating PCzF-mCP-PXZNAI-35 as the emission layer, the solution-processed undoped device showed stable red emission with the maximum emission wavelength (λEL) of 647 nm in the operating voltages 8 V–17 V, the maximum external quantum efficiency (EQEmax) of 0.32% and the maximum luminance (Lmax) of 127 cd/m2. The doped device based on PCzF-mCP-PXZNAI-35 using CBP as host material showed orange-red emission with λEL of 619 nm, EQEmax of 2.34% and Lmax of 1938 cd/m2. This result provides a new strategy for the construction of solution-processable stable red-emitting TADF materials.