Multifunctional assistant acceptor modulated pyrenyl phenanthrimidazole derivatives for highly efficient blue and host-sensitized OLEDs

Abstract

We have designed novel blue emitters, namely, 4-(2-(pyren-1-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PPINCN), 4-(6,9-bis(4-(1,2,2-triphenylvinyl)phenyl)-2-(pyren-1-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PPINCN-TPE) and 4-(6,9-bis(4-(9H-carbazol-9-yl)phenyl)-2-(pyren-1-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PPINCN-Cz) with orthogonal D–A structure to harvest maximum exciton efficiency (EUE) through reverse intersystem crossing (RISC) with hot exciton mechanism. These emitters show hybridized local and charge-transfer (HLCT) states and aggregation-induced emission enhancement (AIEE). The RISC with hot exciton mechanism based on these emitters implies that balanced LE:CT distribution can simultaneously boost photoluminescence efficiency and exciton utilization. The non-doped device with PPINCN-Cz showed maximum efficiency of luminance (L) – 7123 cd m⁻²; current efficiency (CE) – 7.37 cd A⁻¹; power efficiency (PE) – 6.03 lm W⁻¹; external quantum efficiency (EQE) – 5.98%; roll-off efficiency (RO) – 1.33% and exciton utilization efficiency (EUE) – 99.7%. Since nearly 100% EUE has been harvested from the PPINCN-Cz based device, we have used PPINCN-Cz as an emissive dopant and HLCT sensitizing fluorescent host (HLCT-SF). The doped/HLCT-SF device based on PPINCN-Cz showed maximum efficiency of L – 4989/24 081 cd m⁻²; CE – 9.89/29.43 cd A⁻¹; PE – 8.01/26.08 lm W⁻¹; EQE – 9.89/9.82%; RO – 35.9/7.74% and EUE – 90.3/51.9%. The efficient HLCT materials could shed light on a new design strategy towards the improvement of high performance OLEDs.