Approaching Efficient and Narrow RGB Electroluminescence from D–A-Type TADF Emitters Containing an Identical Multiple Resonance Backbone as the Acceptor

Abstract

Highly twisted electron donor (D)–electron acceptor (A)-type thermally activated delayed fluorescence (TADF) emitters can achieve high efficiency while suffering from serious structural relaxations and broad emissions. Multiple resonance (MR)-type TADF emitters can realize narrow emission. However, until now, only a few efficient MR-emitting cores are reported and custom tunning of their emission color remains a major challenge in their wider applications. In this work, by combining the conventional TADF and MR-TADF designs, we demonstrate that color tuning and narrowing the spectral width of conventional TADF emission can be easily achieved simultaneously. We select a prototypical carbonyl (CO)/N-based MR core as a backbone and attach it with D segments of different electron-donating abilities and numbers to obtain three different TADF emitters with emissions from sky blue to green and orange-red while maintaining the narrow emission of the original MR core. The corresponding sky blue, green, and orange-red organic light-emitting diodes achieve maximum external quantum efficiencies of 20.3, 27.3, and 26.3%, respectively, and narrow full widths at half-maximum all below 0.28 eV. These results provide a new molecular design strategy for developing narrowband TADF emitters with easily tunable emissions covering the full visible range.

Efficient circularly polarized thermally activated delayed fluorescence hetero-[4]helicene with carbonyl-/sulfone-bridged triarylamine structures

“…Noticeably, owing to the rigid conjugated skeleton, the fluorescence spectrum of QPO displays a narrow deep blue emission band centred at 431 nm with a full width at half maximum (FWHM) of 33 nm in toluene. 34,36,38,39 Because of the ICT transitions, QPO-PhCz shows a blue emission peak at 447 nm with a larger FWHM of 58 nm 34,48 (Fig. 3).…”

An S-shaped double helicene showing both multi-resonance thermally activated delayed fluorescence and circularly polarized luminescence

“…41,42 These so-called multi-resonant TADF (MR-TADF) emitters rely on p-and n-doping of polycyclic aromatic hydrocarbons to limit the overlap between the HOMO and the LUMO electron-density and thus produce a small DE ST , while their rigid molecular structure results in negligible conformational reorganization in the excited state, and narrowband emission. 40,42,43 There are now examples of blue, [44][45][46][47][48] green [48][49][50][51][52] and red 43,53,54 MR-TADF materials used as emitters in high-efficiency OLEDs. [55][56][57] The study and exploitation of CPL has accelerated over the past decade due to a recognition that employing CPL-active compounds can lead to an increased efficiency of OLEDs and other optoelectronic devices.…”

A deep blue thermally activated delayed fluorescence emitter: balance between charge transfer and color purity

“…15,38 Further, most of the MR-TADF based emitters suffer from poor luminance. 39,40 In order to overcome this limitation, conventional TADF emitters need to be designed and focused to achieve high color purity along with high device brightness as well as performance. Recently, several attempts were made to improve color purity and device performance using conventional TADF molecular design (Table S8, ESI †).…”