Blue thermally activated delayed fluorescence emitters incorporating acridan analogues with heavy group 14 elements for high-efficiency doped and non-doped OLEDs

Blue thermally activated delayed fluorescence emitters incorporating phenazasiline and phenazagermine as donor units are developed, and their structural, photophysical, and electroluminescent properties are systematically investigated.

After the solvent was removed in vacuo, anhydrous toluene (20 mL) was added and the suspension was vigorously stirred. The inorganic salts were removed by filtration and solvent was removed in vacuo. The crude product was used for the next reaction without purification.
After the addition of water, the product was extracted with AcOEt. The combined organic layers were washed with brine and dried over anhydrous Na2SO4. After filtration and evaporation, the crude product was purified by column chromatography on silica gel (eluent: hexane/toluene = 4:1, v/v) to afford Bn-MFASi as a white solid (yield = 2.94 g, 88%). 1

2',8'-Dimethyl-5'H-spiro[dibenzo[b,d]silole-5,10'-dibenzo[b,e][1,4]azasiline] (MFASi):
A suspension of Bn-MFASi (1.40 g, 3.00 mmol) and 5% Pd/C (321 mg) in a mixed solvent of CH2Cl2 (7.5 mL) and AcOH (7.5 mL) was vigorously stirred under H2 atmosphere at room temperature for 15 h. After the reaction mixture was filtered through a Celite ® pad, the filtrate was neutralized with an aqueous solution of NaHCO3. The product was extracted with CH2Cl2, and then washed with brine and dried over anhydrous Na2SO4. After filtration and evaporation, the crude product was purified by column chromatography on silica gel (eluent: hexane/CH2Cl2  (1.54 g, 3.00 mmol) and 5% Pd/C (320 mg) in a mixed solvent of CH2Cl2 (7.5 mL) and AcOH (7.5 mL) was vigorously stirred under H2 atmosphere at room temperature for 24 h. After the reaction mixture was filtered through a Celite ® pad, the filtrate was neutralized with an aqueous solution of NaHCO3. The product was extracted with CH2Cl2, and then washed with brine and dried over anhydrous Na2SO4. After filtration and evaporation, the crude product was purified by column chromatography on silica gel (eluent: hexane/CH2Cl2

Electrochemical Analysis
Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed using an ALS CHI 612E electrochemical analyzer and a three-electrode cell equipped with Pt working and counter electrodes and an Ag/AgNO3 reference electrode. The measurements were carried out for CH2Cl2 solutions of 1-5 (1 mM) at a scanning rate of 50 mV s −1 . Tetrabutylammonium perchlorate (n-Bu4NClO4) was used as a supporting electrolyte with a concentration of 0.1 M.
The redox potentials were calibrated with ferrocene as an internal standard.

Photophysical Properties
UV-vis absorption spectra were measured with a Jasco V-670 spectrometer. Fluorescence and phosphorescence spectra were measured with a Jasco FP-8600 spectrophotometer.
Absolute photoluminescence quantum yields (ΦPL) were determined with a Jasco ILF-835 integrating

Computational Methods
Geometry optimization for 1-5 in the S0 state were performed using the B3LYP functional with the 6-31G(d) basis set in the gas phase, implemented in the Gaussian 16 program package. 6 The transition-state (TS) geometries were optimized using TS keyword. It was confirmed that the transition states show only one negative imaginary frequency and the optimized structures displaced in the direction of negative frequency from the TS geometries are identical to the QA or QE geometries. The population ratios between QE and QA were estimated by Boltzmann distribution as follows, where ΔG are the relative Gibbs free energy changes, kb is the Boltzmann constant, and T is the temperature (298 K). The population ratios were calculated considering that there are two enantiomeric isomers in QA for the rotation of donor and acceptor units.
The geometries of the S1 and T1 states were optimized using the TD-DFT method at the

Fig. S18
Kohn-Sham molecular orbitals of 1-4 most involved in the vertical excitations for the S1 states, calculated at the LC-ωPBE/6-31+G(d) level in the optimized S0 geometries.

OLED Fabrication and Evaluation
Indium tin oxide-coated glass substrates were cleaned with detergent, deionized water, acetone, and isopropanol. They were then treated with UV-ozone treatment for 30 min, before being loaded into a vacuum evaporation system. The organic layers were thermally evaporated on the substrates under vacuum (< 1 × 10 −4 Pa) with an evaporation rate of < 1 Å s -1 . All of the layers were deposited through a shadow mask. The layer thickness and deposition rate were monitored in situ during deposition by an oscillating quartz thickness monitor. OLED properties were measured using a Keithley source meter 2400 and a Konica Minolita CS-2000. Luminance (L), external EL quantum efficiency (ηext), current efficiency (ηc), and power efficiency (ηp) were corrected by Lambertian factors of the devices estimated from the angular dependence of the EL intensity.