advances.sciencemag.org/cgi/content/full/6/41/eaba7855/DC1

Supplementary Materials for

Acceptor plane expansion enhances horizontal orientation of thermally activated

delayed fluorescence emitters

Yepeng Xiang, Pan Li, Shaolong Gong*, Yu-Hsin Huang, Chun-Yu Wang, Cheng Zhong, Weixuan Zeng, Zhanxiang Chen, Wei-Kai Lee, Xiaojun Yin, Chung-Chih Wu*, Chuluo Yang*

*Corresponding author. Email: slgong@whu.edu.cn (S.G.); wucc@ntu.edu.tw (C.-C.W.); clyang@szu.edu.cn (C.Y.)

Published 9 October 2020, Sci. Adv. 6, eaba7855 (2020)

DOI: 10.1126/sciadv.aba7855

This PDF file includes:

General Information Photophysical Characterization The Fitting of Transient Photoluminescence Decay Curves and Analyses of Rate Constants X-Ray Structural Analysis of PXZPyPM Determination of the Emitting Dipole Orientation of an Emitting Layer Calculation of Thin-Film Emission Characteristics, OLED Optical Out-Coupling Efficiency and Theoretical External Quantum Efficiency Synthesis and Characterization of PXZPyPM and PXZTAZPM Figs. S1 to S10 Tables S1 to S4

General Information:

All the reagents and solvents used for the synthesis or measurements were

commercially available, and used as received unless otherwise stated. The 1H NMR

and 13

C NMR spectra were recorded on Bruker Advanced II (400 MHz) spectrometer

with CDCl3 CD2Cl2 or DMSO-d6 as the solvent and tetramethylsilane (TMS) as an

internal reference. Elemental analysis of carbon, hydrogen, and nitrogen was

performed on a Vario EL III microanalyzer. Molecular masses were determined by a

Thermo Trace DSQ II GC/MS. Thermogravimetric analysis (TGA) and differential

scanning calorimetry (DSC) were performed on NETZSCH STA 449C instrument

and NETZSCH DSC 200 PC unit under a nitrogen atmosphere, respectively. The

thermal stability of the samples was determined by measuring their weight loss,

heated at a rate of 10 oC min

-1 from room temperature to 600

oC. The decomposition

temperature (Td) was determined as the temperature that corresponds to 5% weight

loss of the initial weight of the compounds. The glass transition temperature (Tg) was

determined from the second heating scan at a heating rate of 10 oC min

-1 from -60 to

200 oC. Cyclic voltammetric (CV) studies of the compounds were carried out in

nitrogen-purged dichloromethane (CH2Cl2) at room temperature with a CHI

voltammetric analyzer. n-Bu4PF6 (0.1 M) was used as the supporting electrolyte. The

conventional three-electrode configuration consists of a platinum working electrode, a

platinum wire auxiliary electrode, and an Ag wire pseudo-reference electrode with

ferrocene (Fc/Fc+) as the external standard. The HOMO energy levels (eV) of the

compounds were calculated according to the formula: -[4.8+(E1/2(ox/red)-E1/2(Fc/Fc+))]eV.

The LUMO energy levels (eV) of the compounds were calculated by using HOMO

levels and energy gap. The energy levels of S1 and T1 were calculated based on the

onset wavelengths of fluorescence (300 K), fluorescence (77 K) and phosphorescence

(77 K) spectra of three emitters in the mCPCN host (6.0 wt.%). Then the ΔEST values

were obtained on the basis of the equation of ΔEST = S1 (77 K) - T1 (77 K).

Photophysical Characterization:

Synthesized compounds were subjected to purification by temperature-gradient

sublimation in high vacuum before use in subsequent studies. Thin films for

photophysical characterization were prepared by thermal evaporation on quartz

substrates at 1-2 Å/sec in a vacuum chamber with a base pressure of

The integration time window used for phosphorescence measurements was 1 ms.

Photoluminescence quantum efficiency (PL) was characterized by a

spectrofluorimeter (FluoroMax-P, Horiba Jobin Yvon Inc.). PLs of thin films were

determined using the spectrofluorimeter equipped with a calibrated integrating sphere.

During the PL measurements, the integrating sphere was purged with pure and dry

nitrogen to keep the environment inert. The selected monochromatic excitation light

of 325 nm was used to excite samples placed in the calibrated integrating sphere.

There were at least five independent samples for the PL measurements of each

emitter/host system.

The Fitting of Transient Photoluminescence Decay Curves and Analyses of Rate

Constants:

The lifetimes of transient photoluminescence decay curves of emitters were fitted

based on the following equations:

Bi-exponential Fitting N (t) = Ae-t τp⁄ +Be-

tτd⁄ +C I

chi-square = ∑(Nfitting-Nexperiment)

2

Nexperiment

X = A+B

a = A/X, b = B/X

Y = aτp + bτd

Фp = (aτp/Y) ФPL, Фd = (bτd1/Y) ФPL

The rate constants were calculated by assuming knr, S 90%). The rate constants of

radiation (kr), ISC (kISC) and RISC (kRISC) of the emitters were obtained based on the

following equations:

kp= 1

τp II

kd=

1

τd III

kr = Φpkp + Φdkd ≈ Φpkp IV

kISC=

Φd

Φd+Φp*kp ≈(1-Φp)kp V

kRISC≈ Φd

Φp*kp*kd

kISC VI

X-Ray Structural Analysis:

The single crystal of PXZPyPM was achieved from solvent evaporation method from

chlorobenzene. Single-crystal X-ray-diffraction data were obtained from a Bruker

APEX2 Smart CCD diffractometer through using MoKα radiation (λ = 0.71073 Å)

with a ω/2θ scan mode at 296 K. Structures of the crystals were solved by direct

methods using the APEX2 software. None-hydrogen atoms were refined

anisotropically by full-matrix least-squares calculations on F2

using APEX2, while the

hydrogen atoms were directly introduced at calculated position and refined in the

riding mode. Drawings were produced using Mercury-3.3. CCDC-1860254

(PXZPyPM) contains supplementary crystallographic data. These data can be

obtained free of charge from the Cambridge Crystallographic Data Centre via

www.ccdc.cam.ac.uk/data_request/cif.

Determination of the Emitting Dipole Orientation of an Emitting Layer:

To determine the emitting dipole orientation in a molecular emitting film,

angle-resolved and polarization-resolved photoluminescence measurements were

performed. The sample consisted of a fused silica substrate with the 30-nm-thick

mCPCN film doped with emitters. The sample was attached to a fused silica half

cylinder prism by index matching liquid. The excitation of the samples was performed

with the 325-nm line of the continuous-wave He:Cd laser with a fixed excitation

angle of 45o. The emission angle was changed by use of an automatic rotation stage.

The spectra were resolved by using a p-polarizing filter and were measured by a fiber

optical spectrometer. The angle-dependent p-polarized emission intensity at the peak

wavelength of the PL spectrum of the emitting layer was detected. The emitting

dipole orientation (the horizontal dipole ratio Θ//) was then determined by least square

fitting of the measured angle-dependent p-polarized emission intensity with calculated

results.

Calculation of Thin-Film Emission Characteristics, OLED Optical Out-Coupling

Efficiency and Theoretical External Quantum Efficiency:

The simulation tool used for optical simulation of organic layer structures and OLEDs

is developed by ourselves and is based on the equivalence between molecular

emission through electronic dipole transitions and radiation from classical electrical

dipole antenna. With plane-wave expansion of a dipole field (with each plane-wave

mode being characterized by an in-plane wave vector kt), electromagnetic fields

generated by a radiation dipole embedded in a layered structure is calculated, from

which the distribution of the radiation power into different plane-wave modes and the

far-field radiation can be obtained. Emission characteristics of an emitting layer or an

OLED are calculated by assuming that the emitting layer contains an ensemble of

mutually incoherent dipole radiators with distributions in orientations, locations, and

frequencies. The overall emission characteristics and optical out-coupling efficiencies

of internally generated radiation into air were calculated by locating emitting dipoles

in the emitting layer and by considering the orientational distribution [using the

emitting dipole orientation measured] and the full spectral distribution [using the

photoluminescence spectra of emitting layers] of radiating dipoles. When calculating

the pure optical out-coupling efficiency (ηout), the emitters are assumed to have 100%

emission quantum efficiency. In addition, the refractive indexes (n) and extinction

http://www.ccdc.cam.ac.uk/data_request/cif

coefficient (k) of each material in our device structure are used for calculating ηout (fig.

S1).

fig. S1. Optical parameters. (a) The refractive indexes (n) and (b) extinction

coefficient (k) of each material used in the devices.

The theoretical external quantum efficiency (EQEtheoretical) is estimated using the

following equation:

EQE

theoretical = η

rΦPLγηout VII

where ηr refers to a fraction of radiative excitons, γ represents the charge balance

factor, andФPL is the photoluminescence quantum yield of the emitter doped into the mCPCN host (the doping concentration is 6 wt.%). Assuming the perfect charge

balance (γ = 1) and full harvesting of singlet and triplet excitons (ηr = 1), combined

with the ФPL values of 100% for both PXZPM and PXZPyPM and 93% for PXZTAZPM, as well as the simulated ηout values (34.0%, 39.1%, and 39.7% for the

PXZPM-, PXZPyPM-, and PXZTAZPM-based devices, respectively), the theoretical

EQEs calculated with ФPL ηout are 34.0%, 39.1%, and 36.9% for PXZPM-, PXZPyPM-, and PXZTAZPM-based devices, respectively.

Synthesis and Characterization of PXZPyPM and PXZTAZPM:

fig. S2. Synthetic route of PXZPyPM and PXZTAZPM.

The corresponding halogen precursor of ClPPM and borate precursors were prepared

according to literature precedence (26).

2-(4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (1): To a

mixture of 2-(4-bromophenyl)pyridine (702 mg, 3.0 mmol), bis(pinacolato)diboron

(1.14 g, 4.5 mmol), potassium acetate (1.18 g, 12 mmol) and Pd(dppf)Cl2 (110 mg,

0.15 mmol) was added 50 mL of degassed dioxane. After stirring at 90 oC under an

argon atmosphere for 24 h, the mixture was cooled down to room temperature and

extracted with 3 × 40 mL of dichloromethane. The collected organic phase was

washed with brine and dried with anhydrous Na2SO4. After removal of the solvent,

the residue was purified by column chromatography on silica gel (eluent: petroleum /

ethyl acetate = 5:1, v/v) to afford the product as white solid (400 mg, yield: 47%). 1H

NMR (400 MHz, DMSO-d6 + TMS, 298K) δ [ppm]: δ 8.69 (d, J = 7.3 Hz, 1H), 8.12

(d, J = 8.2 Hz, 2H), 8.00 (d, J = 8.0 Hz, 1H), 7.90 (td, J = 7.8, 1.6 Hz, 1H), 7.80 (d, J

= 8.3 Hz, 2H), 7.39 (dd, J = 7.3, 4.8 Hz, 1H), 1.32 (s, 12H).

2,4-Diphenyl-6-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1,3,5-tria

zine (2): Prepared according to the same procedure as Compound 1 but using

2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine. The residue was purified by column

chromatography on silica gel (eluent: petroleum / ethyl acetate = 5:1, v/v) to afford

the product as white solid (220 mg, yield: 52%). 1

H NMR (400 MHz, DMSO-d6 +

TMS, 298K) δ 8.76 (d, J = 7.9 Hz, 6H), 7.96 (d, J = 8.0 Hz, 2H), 7.76-7.66 (m, 6H),

1.36 (s, 12H).

10,10'-((2-(4-(Pyridin-2-yl)phenyl)pyrimidine-4,6-diyl)bis(4,1-phenylene))bis(10

H-phenoxazine) (PXZPyPM): To a mixture of

10,10'-((2-chloropyrimidine-4,6-diyl)bis(4,1-phenylene))bis(10H-phenoxazine)

(ClPPM) (628 mg, 1.0 mmol),

2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)pyridine (Compound 1)

(422 mg, 1.5 mmol), potassium carbonate (2.76 g, 20 mmol) and Pd(PPh3)4 (35 mg,

0.03 mmol) was added 20 mL of degassed tetrahydrofuran and 10 mL of degassed

water. After stirring at 80 oC under an argon atmosphere for 24 h, the mixture was

cooled down to room temperature and extracted with 3 × 40 mL of chloroform. The

collected organic phase was washed with brine and dried with anhydrous Na2SO4.

After removal of the solvent, the residue was purified by column chromatography on

silica gel (eluent: petroleum/dichloromethane = 1:2, v/v) to afford the product as a

yellow powder (470 mg, yield: 63%). 1H NMR (400 MHz, CD2Cl2-d2 + TMS, 298 K)

δ [ppm]: 8.80 (d, J = 8.6 Hz, 2H), 8.66 (d, J = 6.5 Hz, 1H), 8.53 (d, J = 8.5 Hz, 4H),

8.18 (d, J = 8.6 Hz, 2H), 8.14 (s, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.75 (td, J = 7.8, 1.6

Hz, 1H), 7.53 (d, J = 8.5 Hz, 4H), 7.23 (ddd, J = 7.3, 4.8, 1.0 Hz, 1H), 6.66-6.54 (m,

12H), 6.00 (dd, J = 7.8, 1.5 Hz, 4H). 13

C NMR (100 MHz, CDCl3-d) δ[ppm]: 164.5,

164.2, 156.7, 149.6, 144.0, 141.6, 138.3, 137.4, 137.2, 134.0, 131.5, 130.1, 129.0,

127.2, 123.3, 122.6, 121.7, 121.1, 115.6, 113.3, 110.7. EI-MS m/z: 747.7 [M+] (calcd:

747.3). Elemental analysis for C51H33N5O2: C, 81.91; N, 9.36; H, 4.45. Found: C,

81.78; N, 9.29; H 4.37.

10,10'-((2-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)pyrimidine-4,6-diyl)bis(4,1-

phenylene))bis(10H-phenoxazine) (PXZTAZPM): Prepared according to the same

procedure as PXZPyPM but using

2,4-diphenyl-6-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1,3,5-triazine

(Compound 2). The residue was purified by column chromatography on silica gel

(eluent: dichloromethane) to afford the product as yellow solid (1.20 g, yield: 67%). 1H NMR (400 MHz, CDCl3-d + TMS, 298 K) δ [ppm]: 9.01-8.96 (m, 4H), 8.83 (dd, J

= 8.0, 1.6 Hz, 4H), 8.60 (d, J = 8.5 Hz, 4H), 8.20 (s, 1H), 7.65-7.60 (m, 10H),

6.76-6.63 (m, 12H), 6.07 (dd, J = 7.8, 1.5 Hz, 4H). 13

C NMR (100 MHz, CDCl3-d) δ

[ppm]: 171.8, 171.4, 164.2, 144.0, 141.7, 141.4, 137.3, 136.2, 134.0, 132.7, 131.6,

130.1, 129.2, 129.0, 128.8, 128.7, 123.3, 121.7, 115.7, 113.3, 111.1. EI-MS m/z:

901.8 [M+] (calcd: 901.3). Elemental analysis for C61H39N7O2:

C 81.22, N 10.78, H

4.36. found: C 81.12, N 10.68, H 4.24.

fig. S3. The energy levels and frontier molecular orbitals. (a) Acceptor segments.

(b) PXZPM, PXZPyPM and PXZTAZPM.

table S1. The calculated key parameters of excited states of PXZPM, PXZPyPM

and PXZTAZPM.

Emitter Excite state D* (Å) Sr Orbital contributions

†

PXZPM S1 2.168 0.29498 H-L:0.63; H1-L1:0.207

T1 1.858 0.47834 H1-L:0.467; H-L1:0.187

PXZPyPM S1 3.839 0.21362 H-L:0.565; H-L2:0.088

T1 1.768 0.51693 H2-L1:0.288; H-L:0.161

PXZTAZPM S1 2.584 0.22417 H-L1:0.629; H1-L3:0.136

T1 2.106 0.47393 H1-L1:0.361; H4-L:0.145

*Distance between centroid of hole and electron. †The top two orbital contributions of

excite state.

fig. S4. Structure of PXZPyPM. (a) Single crystal structure (CCDC number:

1860254, Triclinic, P-1) and molecular packing diagram of PXZPyPM with hydrogen

atoms omitted (solvent molecules: chlorobenzene). (b) Comparison between the

single crystal structure (green) and the DFT optimized structure (red) of PXZPyPM.

fig. S5. p-polarized photoluminescence intensity measurements. Different emitting

layers (at photoluminescence peak wavelength) as a function of the emission angle

and simulated curves (lines and dotted lines) with different horizontal dipole ratios Θ//

of (a) PXZPM, (b) PXZPyPM, (c) PXZTAZPM doped into the mCPCN host (3.0, 6.0

and 12.0 wt.%), and (d) PXZPM, PXZPyPM and PXZTAZPM doped into the CBP

host (6.0 wt.%).

fig. S6. Thermal and electrical properties of PXZPyPM and PXZTAZPM. (a)

TGA curves of PXZPyPM and PXZTAZPM. (b) DSC curves of PXZPyPM and

PXZTAZPM. (c) Oxidation behavior of PXZPyPM and PXZTAZPM.

table S2. Thermal, electrochemical and TD-DFT calculation data of PXZPM,

PXZPyPM and PXZTAZPM.

compounds HOMO

*/LUMO

†

(eV)

HOMO/LUMO‡

(eV)

ΔEST§ (eV)

Tg/Td||

(oC)

PXZPM -5.10/-2.42 -4.73/-2.15 0.18 115/488

PXZPyPM -5.08/-2.36 -4.70/-2.05 0.22 162/489

PXZTAZPM -5.10/-2.44 -4.74/-2.22 0.20 185/503

*Obtained from Cyclic voltammograms in CH2Cl2 solution at room temperature; †LUMO = HOMO

a + Eg;

‡Estimated from DFT calculations. §Estimated from the

excited state analysis of S1 and T1. ||Measured by DSC or TGA.

fig. S7. Solvatochromic measurements. Normalized photoluminescence spectra of

(a) PXZPM, (b) PXZPyPM, and (c) PXZTAZPM (10-5

M) in toluene, chlorobezene,

tetrahydrofuran, and chloroform at 300 K (Excitation wavelength: 400 nm).

fig. S8. Transient photoluminescence decay curves in the mCPCN host. The

transient photoluminescence decay spectra and fitting curves of 6.0 wt.% (a) PXZPM,

(b) PXZPyPM, and (c) PXZTAZPM doped into the mCPCN host at 300 K, following

excitation at 377 nm, detected at 521, 524, and 528 nm (photoluminescence peak

wavelength), respectively. The time-resolved photoluminescence spectra (20 and 5000

ns) of 6.0 wt.% (d) PXZPM, (e) PXZPyPM, and (f) PXZTAZPM doped into the

mCPCN host at 300 K (Excitation wavelength: 377 nm). The transient

photoluminescence decay spectra of 6.0 wt.% (g) PXZPyPM and (h) PXZTAZPM

doped into the mCPCN host from 100 to 300 K, following excitation at 377 nm,

detected at 524 and 528 nm (photoluminescence peak wavelength), respectively.

fig. S9. Photoluminescence properties of PXZPM, PXZPyPM, and PXZTAZPM

doped into the PMMA films. Normalized fluorescence (300 K) and phosphorescence

(77 K) spectra of 6.0 wt.% (a) PXZPM, (b) PXZPyPM, and (c) PXZTAZPM doped

into the PMMA films (Excitation wavelength: 365 nm). The transient

photoluminescence decay spectra and fitting curves of 6.0 wt.% (d) PXZPM, (e)

PXZPyPM, and (f) PXZTAZPM doped into the PMMA films at 300 K, following

excitation at 377 nm, detected at 516, 518, and 517 nm (photoluminescence peak

wavelength), respectively. The time-resolved photoluminescence spectra (20 and 5000

ns) of 6.0 wt.% (g) PXZPM, (h) PXZPyPM, and (i) PXZTAZPM doped into the

PMMA films at 300 K (Excitation wavelength: 377 nm).

fig. S10. Electroluminescence performance of devices. (a) Current

density-voltage-luminance curves of the devices based on emitting layers with

different doping concentrations of PXZPyPM emitter in the mCPCN host (Inset:

Electroluminescence spectra of the devices). (b) Power efficiency and external

quantum efficiency versus luminance curves of the PXZPyPM-based devices. (c)

Current density-voltage-luminance curves of the devices based on emitting layers

with different doping concentrations of PXZTAZPM emitter in the mCPCN host

(Inset: Electroluminescence spectra of the devices). (d) Power efficiency and external

quantum efficiency versus luminance curves of the PXZTAZPM-based devices.

table S3. Summary of electroluminescence characteristics for the devices based

on PXZPyPM and PXZTAZPM.*

compounds Doping concentration (wt.%) ELpeak (nm) EQE (%) PE (lm W-1

)

PXZPyPM

3 521 30.3 101.0

6 528 32.2 119.6

12 534 31.4 118.2

PXZTAZPM

3 522 26.9 82.2

6 530 30.1 101.5

12 536 25.0 90.6

*The device structure is ITO/MoO3 (1 nm)/TAPC (50 nm)/mCP (10 nm)/mCPCN: x

wt.% PXZPyPM or PXZTAZPM (20 nm)/3TPYMB (50 nm)/LiF (0.5 nm)/Al.

table S4. Summary of performances of green to yellow TADF emitters (500 nm <

ELmax < 580 nm) with high external quantum efficiency (EQEmax > 30%).

Compounds ELmax (nm) EQEmax (%) PEmax (lm W

-1) Ref.

CzDBA 528 37.8 121.6 15

tBuCzDBA 542 32.4 109.8 15

cis-BOX2 518 33.4 - 20

Pm2 526 31.3 117.2 27

Pm5 541 30.6 116.3 27

4CzIPN 512 31.2 - 28

PXZPyPM 528 33.9 118.9 This work

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