Manipulating Spectral Width and Emission Wavelength towards Highly Efficient Blue Asymmetric Carbazole Fused Multi-Resonance Emitters

Abstract

The novel carbazole-based multiresonance types of thermally activated delayed fluorescence (MR-TADF) emitters of mICz-DABNA and BFCz-DABNA are reported, and their spectroscopic properties are investigated with the inductive effect on the central nitrogen atom for pure and deep blue emission. With the introduction of electron-donating/-withdrawing properties of substituents, emitters exhibited the bathochromic/hypsochromic shifted emission, respectively, compared to simple carbazole-based MR-TADF. Moreover, their spectral bandwidths became narrower. Theoretical calculation indicated that the meta-positioned bulky moiety restricts the molecular geometry discrepancy and reduces the Huang−Rhys factors. Particularly, the organic light-emitting diode (OLED) with 3% BFCz-DABNA exhibited the maximum external quantum efficiency of 28.0% with the Commission International de l'E ́clairage (CIE) of (0.13, 0.09), which is the best record value among single-boron MR-TADF devices of CIE y < 0.10.

Rational Molecular Design Strategy for High-Efficiency Ultrapure Blue TADF Emitters: Symmetrical and Rigid Sulfur-Bridged Boron-Based Acceptors

“…Furthermore, the device of TSBA-Cz and TSBA-PhCz showed a high EQE of 23.4 and 21.3% at the maximum, a maximum PE of 24.4 and 24.1 l m W –1 , and a maximum CE of 25.6 and 25.4 cd A –1 , respectively. The EQE values of two emitters are at comparatively high levels for the ultrapure blue D–A-type TADF emitters with CIE y < 0.11. ,− Such high device performance and excellent color purity of these two emitters indicate that they are advantageous for the application of various ultrapure blue TADF-OLED devices.…”

Intramolecular Cyclization: A Convenient Strategy to Realize Efficient BT.2020 Blue Multi‐Resonance Emitter for Organic Light‐Emitting Diodes

“…The small E reo value contributes to the smallest Stokes shift and narrowest band emission in CZ2CO. [32][33][34][35][36] Vibrationally resolved fluorescence spectra are calculated to determine the main vibration of the S 1 !S 0 (first singlet excited state to ground state) transition. As shown in Figure 2b-d and Table S3, CZCO shows the most blue-shifted emission while CZ2CO exhibits the smallest FWHM with 358 cm À 1 (6 nm), which is consistent with the experimental trends.…”

“…The E reo value of CZ2CO turns out to be only about half of those of QAO and CZCO (0.131 vs. 0.260 eV and 0.277 eV), which is the combined result of the above‐mentioned factors and proves the molecular design concept. The small E reo value contributes to the smallest Stokes shift and narrowest band emission in CZ2CO [32–36] . Vibrationally resolved fluorescence spectra are calculated to determine the main vibration of the S 1 →S 0 (first singlet excited state to ground state) transition.…”

Recent progress and prospects of fluorescent materials based on narrow emission

“…4 (a-y) Chemical structures of emitters discussed in Section 3.1.1. 26,[32][33][34][38][39][40][41][42][43][44][47][48][49][50][51][52][53][54][55][56][57][58][59] This journal is © The Royal Society of Chemistry 2023…”

“…Recently, a new approach using lateral peripheral moiety substitution on the MR core that can affect the electron density of the nearby nitrogen atom was proposed for blue MR-TADF by Kwon et al 49 The report contained two structurally related emitters, mICz-DABNA and BFCz-DABNA (Fig. 4n) (contrast molecule: DPACzBN2 ).…”