Fig. 1. Comparison between D-A type TADF materials and MR-TADF materials

Fig. 2. Comprehensive overview of MR-TADF materials. (a) Classification of MR-TADF materials and comparison of MR-TADF materials with single boron structure and multi-boron structure; (b) development history of MR-TADF materials with multi-boron structures

Fig. 3. Device performance of ν-DABNA^[36]. (a) HOMO and LUMO of a conventional emitter (left, perylene) and proposed emitter (right, ν-DABNA); (b) energy level diagrams of the materials used in OLEDs; (c) normalized EL spectra; (d) EQE versus luminance characteristics (insert: molecular structures of ν-DABNA)

Fig. 4. Type 1 of U-shaped conjugated double-boron blue MR-TADF materials^[37]

Fig. 5. Type 2 of U-shaped conjugated double-boron blue MR-TADF materials^[39]

Fig. 6. Type 3 of U-shaped conjugated double-boron blue MR-TADF materials^[45]

Fig. 7. Photophysical properties and device performance of o-Tol-ν-DABNA-Me^[46]. (a) Normalized absorption spectra of o-Tol-ν-DABNA-Me in THF at concentration of 10^-5 mol/L and steady-state PL spectra of 30% (mass fraction) DBA-SAF doped DBFPO film and DBA-SAF in toluene (0.05 mmol/L); (b) steady-state PL spectra for 3% (mass fraction) o-Tol-ν-DABNA-Me∶DBFPO binary film and for o-Tol-ν-DABNA-Me (mass fraction of 3%)∶DBA-SAF (mass fraction of 30%)∶DBFPO ternary film; (c) excimer binding energy distributions for ν-DABNA and o-Tol-ν-DABNA-Me; (d) calculated nonbonding energy and separated van der Waals energy for each individual system integrated from 20 ns converged frames; (e) J-V-L characteristics of tested OLED; (f) CE‒luminance curves of tested OLEDs; (g) EQE‒luminance curves of tested OLED devices

Fig. 8. Structure and photophysical properties of V-shaped conjugated double-boron blue MR-TADF molecules^[48]. (a) V-shaped conjugated double-boron blue MR-TADF molecule; (b) borylation method for 3, 4a, 4b, 5a, and 5b; (c) UV‒vis absorption/emission spectra of 3 in CH₂Cl₂

Fig. 9. Structure and device performance of double-boron blue MR-TADF molecules with ladder-shaped conjugation^[50]. (a) Type 1 of double-boron blue MR-TADF materials with ladder-shaped conjugation; (b) design strategy for ODBN; (c) device performances of ODBN

Fig. 10. Type 2 of double-boron blue MR-TADF materials with ladder-shaped conjugation^[52]

Fig. 11. Type 3 of double-boron blue MR-TADF materials with ladder-shaped conjugation^[57]

Fig. 12. Double-boron blue MR-TADF molecules with double-emitting cores^[59]

Fig. 13. Mesityl-modified double-boron blue MR-TADF molecules^[66]

Fig. 14. Molecular structures and device performances of m[B-N]N1 and m[B-N]N2^[68]. (a) Double-boron blue MR-TADF molecules containing B-N polar bonds; (b) device performances of m[B-N]N1 and m[B-N]N2

Fig. 15. Device performances of DBCz-Mes^[69]. (a) Device configuration, energy level, and molecular structure of the materials used; (b) EL spectra of devices recorded at 10 mA·cm^-2; (c) CIE coordinates of the device; (d) EQE and power efficiency versus luminance of the device (insert: molecular structure of DBCz-Mes)

Fig. 16. Photophysical properties of B3^[49]. (a) Molecular structure of B3; (b) normalized absorption (blue), fluorescence (red), and phosphorescence (green, 77 K, 25 ms delay) spectra of PMMA films of B3; (c) normalized PL spectra of B3 at 77 K with various delay times

Fig. 17. Characteristics of fabricated OLED device using DOB2-DABNA-A (blue) and DOB2-DABNA-B-NP (light blue) as an emitter^[72]. (a) Device structure and ionization potentials (I_p) and electron affinities (E_a; unit in eV) for each component; (b) normalized EL spectra of the devices in operation; (c) CIE coordinates; (d) current density (solid) and luminance (dashed) vs driving voltage; (e) EQE vs luminance; (f) comparison of EQE values at 1000 cd·m^-2 for reported deep-blue OLEDs with CIE y<0.1; (g) comparison of k_RISC values at 1000 cd·m^-2 for reported deep-blue OLEDs with CIE y<0.1

Fig. 18. Tri-boron blue MR-TADF molecules with helical structure^[64]

Fig. 19. Tri-boron blue MR-TADF molecules with linear conjugation^[74]

Fig. 20. Photophysical properties of 10j^[64]. (a) Molecular structure of 10j; (b) normalized UV‒vis absorption and PL spectra of 10j in toluene solution at room temperature; (c) normalized UV‒vis absorption and PL spectra of 10j in toluene solution at low temperature (77 K)

Fig. 21. Photophysical properties of B4^[49]. (a) Molecular structure of B4; (b) normalized absorption (blue), fluorescence (red), and phosphorescence (green, 77 K, 25 ms delay) spectra of PMMA films of B4; (c) normalized PL spectra of B4 at 77 K with various delay times (saturated in 2-methyltetrahydrofuran)

Fig. 22. Theoretical calculation results of DPA-B2, DPA-B3, DPA-B4, and CzB4^[76]. (a) HOMO and LUMO distributions; (b) SOC constants

Fig. 23. Quadruple-boron blue MR-TADF molecules with linear conjugation^[76]

Fig. 24. Device performance of R/S-BDBF-BOH and R/S-BDBT-BOH^[78]. (a) Molecular structures of R/S-BDBF-BOH and R/S-BDBT-BOH; (b) device performances of R/S-BDBF-BOH and R/S-BDBT-BOH

Fig. 25. Photophysical properties of CzB6 and CzB8^[77]. (a) Molecular structures of CzB6 and CzB8; (b)(d) normalized fluorescence (blue, 300 K; red, 77 K) and phosphorescence (green, 77 K, 25 μs delay) spectra of the 0.1%(mass fraction)-doped PS films of CzB6 and CzB8 with absorption/emission maxima, absolute fluorescence quantum yield (Φ), full width at half-maximum, and energy gap between the S₁ and T₁ states (ΔE_ST); (c)(e) transient decay spectrum of CzB6 and CzB8 at 300 K and its relevant parameters, the red curve shows the single exponential fitting (background is 5), the gray line shows the instrument response function (IRF), Φ_F and Φ_TADF indicate quantum yields of the fluorescent and TADF components, respectively, and τ_F and τ_TADF indicate the lifetimes of the fluorescent and TADF components, respectively