Great achievements have been made in the development of organic light-emitting diodes in recent decades. However, achieving high color purity for blue emitters remains a challenge. In this study, we have designed and synthesized three naphthalene (NA)-embedded multi-resonance (MR) emitters, named SNA, SNB and SNB1, based on N-B-O frameworks with isomer variations for finely adjusting the photophysical properties. These emitters show tunable blue emission with emission peaks of 450-470 nm. Small full width of half maximum (FWHM) of 25-29 nm are achieved in these emitters, indicating the well maintaining of molecular rigidity and MR effect with NA extension. Such design also ensures a fast radiative decay. However, no obvious delayed fluorescence is observed in all three emitters due to the relatively large energy differences between the first singlet and triplet excited states. Both SNA and SNB enable high electroluminescent (EL) performance in doped devices with external quantum efficiency (EQE) of 7.2 and 7.9 %, respectively. When applying the sensitized strategy, devices based on SNA and SNB show huge improvement with EQE of 29.3 and 29.1 %. More importantly, SNB with twist geometry enables stable EL spectra with almost unchanged FWHM under different doping concentrations. This work demonstrates the potential of NA extension design in constructing narrowband emissive blue emitters.
Keywords: blue emission; multi-resonance emitter; organic lighting emitting diodes; sensitized devices.
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