Ultra‐Narrowband Blue Multi‐Resonance Thermally Activated Delayed Fluorescence Materials

Abstract

Ultra-narrowband blue multi-resonance-induced thermally activated delayed fluorescence (MR-TADF) materials (V-DABNA and V-DABNA-F), consisting of three DABNA subunits possessing phenyl or 2,6-difluorophenyl substituents on the peripheral nitrogen atoms are synthesized by one-shot triple borylation. Benefiting from the inductive effect of fluorine atoms, the emission maximum of V-DABNA-F (464 nm) is blueshifted from that of the parent V-DABNA (481 nm), while maintaining a small full width at half maximum (FWHM, 16 nm) and a high rate constant for reverse intersystem crossing (6.5 × 10 5 s −1 ). The organic light-emitting diodes (OLEDs) using V-DABNA and V-DABNA-F as emitters are fabricated by vapor deposition and exhibit blue emission at 483 and 468 nm with small FWHMs of 17 and 15 nm, corresponding to Commission Internationale d'Éclairage coordinates of (0.09, 0.27) and (0.12, 0.10), respectively. Both devices achieve high external quantum efficiencies of 26.2% and 26.6% at the maximum with minimum efficiency roll-offs of 0.9% and 3.2%, respectively, even at 1000 cd m −2 , which are record-setting values for blue MR-TADF OLEDs.

Solution‐Processable Ultrapure‐Blue Light‐Emitting Electrochemical Cells

“…These results closely match the requirements for the recent standard blue color display reported by the National Television System Committee: CIE color coordinates of (0.14, 0.08) and FWHM <30 nm (Figure S17, Supporting Information). [ 16–20 ] Particularly, the CIE coordinates of DABNA‐4TBC are almost identical to those of the standard blue color provided by the National Television System Committee. Additionally, these CIE coordinates closely resembled the CIE color coordinates (0.131, 0.046) of the next‐generation standard blue display recommended by the International Telecommunication Union (ITU‐R, BT.2100).…”

“…Particularly, urgent improvements are required to effectively achieve blue light emission in LECs, considering that recent displays require blue light emissions with an emission color close to the Commission Internationale de l'éclairage (CIE) coordinates of (0.14, 0.08) and a full-width at half-maximum (FWHM) <30 nm. [16][17][18][19][20] Organic materials exhibit a broadening effect, which is caused by vibronic coupling between the ground and singlet excited states, as well as structural relaxation in the singlet excited state. Consequently, limited progress has been made in terms of the color purity and FWHM of blue-light-emitting LECs based on metal-free materials.…”

“…Recently, Hatakeyama et al proposed multi-resonance-induced thermally activated delayed fluorescence (MR-TADF) materials and fabricated organic light-emitting diodes (OLEDs) with high color purity using the DABNA series. [18][19][20] In these materials, boron, and nitrogen atoms are inserted into the benzene ring to suppress structural relaxation, resulting in the separation of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) into different carbon atoms in the benzene ring owing to the multiple resonance effect. This leads to the suppression of vibrational structures and ultra-narrow-band blue emission without using precious metals.…”

A comparative study of two multi-resonance TADF analogous materials integrating chalcogen atoms of different periods

“…Multi-resonance (MR) type thermally activated delayed fluorescence (TADF) compounds have been receiving particular attention over the past few years, for their bright prospects to enable organic light-emitting diodes (OLEDs) to have high efficiency and high color purity simultaneously. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In MR-featuring compounds, electron donating/withdrawing atoms/groups (e.g., boron (B)/nitrogen (N) atoms) are typically on the opposite sites of a polyaromatic framework. The bonding/anti-bonding characteristics between the adjacent atoms are thus minimized and the non-bonding orbitals can minimize structural relaxation and vibrational couplings.…”

“…Multi-resonance (MR) type thermally activated delayed fluorescence (TADF) compounds have been receiving particular attention over the past few years, for their bright prospects to enable organic light-emitting diodes (OLEDs) to have high efficiency and high color purity simultaneously. 1–19 In MR-featuring compounds, electron donating/withdrawing atoms/groups ( e.g. , boron (B)/nitrogen (N) atoms) are typically on the opposite sites of a polyaromatic framework.…”