High Triplet Energy Level Achieved by Tuning the Arrangement of

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High Triplet Energy-Level Achieved by Tuning the Arrangement of Building Blocks in Phosphorescent Polymer Backbones for Furnishing High Electroluminescent Performances in Both Blue and White Organic Light-Emitting Devices Boao Liu, Feifan Dang, Zhuanzhuan Tian, Zhao Feng, Deyuan Jin, Wanping Dang, Xiaolong Yang, Guijiang Zhou, and Zhaoxin Wu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 26 Apr 2017 Downloaded from http://pubs.acs.org on April 28, 2017

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ACS Applied Materials & Interfaces

High Triplet Energy-Level Achieved by Tuning the Arrangement of Building Blocks in Phosphorescent Polymer Backbones for Furnishing High Electroluminescent Performances in Both Blue and White Organic Light-Emitting Devices Boao Liu,† Feifan Dang,† Zhuanzhuan Tian,† Zhao Feng,† Deyuan Jin,† Wanping Dang,† Xiaolong Yang,† Guijiang Zhou,*,†, ¶ Zhaoxin Wu,*, ‡

†

MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter,

Institute of Chemistry for New Energy Material, Department of Chemistry, School of Science, Xi’an Jiaotong University, Xi’an 710049, P. R. China. ¶

State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an

710049, P. R. China. ‡

Key Laboratory of Photonics Technology for Information, School of Electronic and

Information Engineering, Xi’an Jiaotong University, Xi’an, 710049, P. R. China

1

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ABSTRACT: High triplet energy-level (ET) of ca. 2.83 eV has been achieved in novel polymer backbone through tuning the arrangement of two kinds of building blocks showing enhanced hole injection/transporting capacity. Based on this new polymer backbone with high ET, both blue and white phosphorescent polymers were successfully developed with trade-off between high ET and enhanced charge carrier transporting ability for these polymer backbones. In addition, their photophysical features, electrochemical behaviors and electroluminescent (EL) properties have been characterized in detail. Benefitted from the advantages associated with the novel polymer backbone, the blue phosphorescent polymers can furnish top-ranking EL performances with maximum luminance efficiency (ηL) of 15.22 cd A−1, corresponding to power efficiency (ηP) of 12.64 lm W−1 and external quantum efficiency (ηext) of 6.22% and the stable CIE coordinates of (0.19, 0.38). Furthermore, blue-orange (B-O) complementary-colored white phosphorescent polymers based on this novel polymer backbone have also been obtained to show encouraging EL efficiencies of 12.34 cd A−1, 9.59 lm W−1 and 4.10% in the optimized WOLED together with exceptionally stable Commission Internationale de L’Eclairage (CIE) cooridicates of (∆x = 0.014, ∆y = 0.010) in wide driving voltage range from 4 V to 16 V. All these attractive EL results achieved by these novel phosphorescent polymers can show the great potential of this new polymer backbone in developing highly efficient phosphorescent polymers. KEYWORDS: phosphorescent polymers, high triplet energy-level, polymer backbone, OLEDs, charge carrier injection/transporting, functionalization

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INTRODUCTION Phosphorescent polymers can show their intrinsic advantages in constructing organic light-emitting devices (OLEDs) by both employing highly efficient triplet emitters and convenient solution-processed device fabrication.1-8 Similar to their small molecular counterparts,9-17 Phosphorescent polymers can achieve much higher electroluminescent efficiencies compared with fluorescent analogs.1-6 Furthermore, they can successfully cope with the problem of phase separation, i.e., aggregation of phosphorescent emitters in the doped systems in which small molecular phosphorescent emitters are mixed with polymeric hosts.18-22 In order to enhance the solubility of phosphorescent polymers for device fabrication with convenient spin-coating method, long alkyl chains have been introduced. Clearly, these non-electroactive alkyl chains will definitely hamper charge carrier injection/transporting processes of emission layer (EML) deposited by these polymeric emitters. On the bases of the working mechanism of OLEDs,23-28 charge carrier injection/transporting processes are very crucial for the electroluminescent (EL) performances of OLEDs.29-31 Hence, conjugated backbones are typically adopted in phosphorescent polymers in order to elevate their ability of charge

carrier

injection/transporting.32-42

Unfortunately,

conjugated

backbones

in

phosphorescent polymers typically possesses low-energy non-emissive triplet states, which greatly enhance the opportunity of undesired back energy-transfer processes from the emissive triplet states of the phosphorescent cites to the non-emissive triplet states for the conjugated polymer backbones.43-46 Hence, this situation will lead to significant reduction of device performances. Clearly, back energy-transfer issue should be paid more attention in blue- and white-emitting polymers containing blue phosphorescent chromophores which possess relatively high triplet energy level (ET) to raise the possibility of back energy-transfer processes. With the 3



purpose of dealing with the problem of back energy-transfer, phosphorescent polymers with non-conjugated back-bones have been prepared,21-22,

43-49

which will obviously disfavor the

ability of charge carrier injection/transporting. Either Blue(B)-Orange(O) complementary or Red(R)-Green(G)-Blue(B) primary color strategy, blue phosphorescent emitters are typically employed to develop single white-emitting phosphorescent polymers,32-39, 45-46, 50-51 which can be used to fabricate white OLEDs (WOLEDs) conveniently by solution process instead of complicate vacuum deposition technique. As the most promising candidate of future lighting sources, WOLEDs have to show high EL efficiencies.1-2 So, back energy-transfer problem should be avoided in single white-emitting phosphorescent polymers as well.3, 6, 52-56 From what aforementioned, there is a controversy between high ET polymer backbone and charge carrier injection/transporting ability of blue- and white phosphorescent polymers. So, realizing optimized trade-off between these two features should be of great importance for developing high-performance blue- and white phosphorescent polymers. In this contribution, novel backbone of blue-emitting phosphorescent polymers has been developed through coupling 3,6-positions of carbazole-based monomers with 9-position of fluorene units. Furthermore, white-emitting phosphorescent polymers of B-O complementary color have been prepared as well. Through the perpendicular arrangement between carbazole and fluorene units, ET of these new polymer backbone has been elevated to effectively block back energy-transfer process. At the same time, carbazole-based unit has been employed to promote hole injection/transporting ability of the concerned polymers.

RESULTS AND DISCUSSION Design and Synthesis. The synthesis of the blue IrIII phosphorescent monomers M-IrB and the 4


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orange-emitting analog M-IrO (Scheme 1) is very crucial for the preparation of the target blue and

white

phosphorescent

polymers

(Scheme

1),

since

the

organic

monomers

9-(4-(hexyloxy)phenyl)carbazole (CzPhOC6) and fluorenone (FlO) can be easily prepared according to literature method. The synthetic detail for organic monomers CzPhOC6 and FlO has been provided in Supporting Information (SI, Scheme S1). In order to obtain M-IrB and M-IrO, two key organic intermediate picolinic acid derivatives CzOPicOH and CzPicOH have to be prepared at first as auxiliary ligands of the IrIII phosphorescent monomers (Scheme 1). The synthesis of CzOPicOH is started by the preparation PicMe through esterification of 6-hydroxypicolinic acid with MeOH. Then, PicMe couples

with

1-(2-bromoethoxy)-4-iodobenzene

(IPhOBr)

prepared

by

excess

1,2-dibromoethane and 4-iodophenol to obtain PicOPhI (Scheme 1). Though Suzuki cross-coupling reaction between PicOPhI and 4-(N-carbazol)phenylboronic acid (CzPhB), the precursor compound CzOPicMe can be synthesized in high yield. Then, picolinic acid derivative CzOPicOH can be successfully synthesized by hydrolysis of CzOPicMe under base condition (Scheme 1). However, the synthesis of picolinic acid derivative CzPicOH is much easier, since its precursor compound CzPicMe can be obtained conveniently by Suzuki cross-coupling reaction between 6-bromomethylnicotinate and CzPhB. Similarly, CzPicOH is synthesized in high yield by the hydrolysis of CzPicMe. After obtaining the key intermediate picolinic acid derivatives CzOPicOH and CzPicOH, the IrIII phosphorescent monomers M-IrB and M-IrO can be prepared easily by the reaction of the corresponding IrIII dimmer complexes Ir[dFppy]2Cl257 and Ir[PyFl]2Cl258 with Na2CO3 as base (Scheme 1). With the aim of avoiding bathochromic effect in phosphorescent wavelength of blue-emitting M-IrB, picolinic acid unit has

been

attached

to

the

9-(biphenyl-4-yl)carbazole 5


unit

through

non-conjugated


ethylenedioxide linker (Scheme 1). On the contrary, picolinic acid unit is attached to 9-phenylcarbazole unit directly in M-IrO.

Scheme 1. Synthetic protocols for the phosphorescent IrIII monomers.

After obtaining the crucial IrIII phosphorescent monomers M-IrB and M-IrO, the designed 6


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phosphorescent polymers can be prepared according to the protocols in Scheme 2. With the Eaton’s reagent (the solution of phosphorus pentoxide in methanesulphonic acid, 7.5 wt%), the 3,6-positions of the carbazole unit in both CzPhOC6 and M-IrB react with the 9-position of fluorenone (FlO) to form the backbone of the blue phosphorescent polymers. Through tuning the feeding ratio of the three monomers, the blue phosphorescent polymers with different content of blue phosphorescent units have been prepared as ca. 2.0 wt % for P-B-1, 4.0 wt % for P-B-2, 6.0 wt % P-B-3 and 8.0 wt % for P-B-4, respectively (Scheme 2). Following the similar strategy, white phosphorescent polymers have been successfully prepared as well (Scheme 2). Based on the mole-ratio among different monomers in Scheme 2, the content of the phosphorescent units in all three white phosphorescent polymers has been maintained at ca. 10.0 wt %. The weight-ratio between blue and orange phosphorescent units in the white-emitting polymers has been set at ca. 15 : 1 for P-W-1, 20 : 1 for P-W-2 and 30 : 1 for P-W-3 in order to optimize their white emission spectra. In order to investigate the property of backbone of these phosphorescent polymers, organic model polymer P-Org has also been prepared (Scheme 2). Gel-permeation chromatography (GPC) measurements have indicated the formation of high-molecular-weight phosphorescent polymers (Mw in the range from 1.6×104 − 1.9×104 g mol–1) with a relatively narrow polydispersity index (PDI = 1.3 − 1.6). Scheme 2. Synthetic protocols for both blue and white phosphorescent polymers

7



F

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F N

F

F

Ir N

O N

O

O O

O

N

N

M-IrB Eaton's Reagent

x

z y1

y2

n P-B-1 x : (y1+y2) : z = 99.01 : 100 : 0.99 P-B-2 x : (y1+y2) : z = 98.02 : 100 : 1.98 P-B-3 x : (y1+y2) : z = 96.93 : 100 : 3.74 P-B-4 x : (y1+y2) : z = 95.79 : 100 : 4.21

O

O

N O Eaton's Reagent +

N

Fluorenone CzPhOC6

n P-Org F

F N

F

F

Ir N

O O

N

O N

O

O

O

Ir N O

O

N

M-IrB

M-IrO

Eaton's Reagent

N

N

N

x1

x2

z y1

N

y2

y3

w

y4

n P-W-1 (x1+x2) : (y1+y2+y3+y4) : z : w = 94.40 : 100 : 5.29 : 0.31 P-W-2 (x1+x2) : (y1+y2+y3+y4) : z : w = 94.47 : 100 : 5.29 : 0.24 P-W-3 (x1+x2) : (y1+y2+y3+y4) : z : w = 94.54 : 100 : 5.29 : 0.17

Thermal and Optical Properties. Thermal properties of the phosphorescent polymers are fully characterized using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA and DSC curves and the corresponding data are provided in Figure 1 and Table 1. TGA measurements have revealed that both blue and white phosphorescent polymers exhibit high thermal stability with obvious decomposition temperature (Td) above 400 oC (Figure 1a and Table 1). In particular, for the blue phosphorescent polymers, their Td gradually decreases with 8


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increasing the content of IrIII phosphorescent monomer M-IrB (ca. 457 oC for P-B-1, 449 oC for P-B-2, 443 oC for P-B-3 and 439 oC for P-B-4) (Figure 1a and Table 1) on account of their lower thermal stability for blue phosphorescent units (e.g., Td = 335 oC for M-IrB). For the white phosphorescent polymers, P-W-1, P-W-2 and P-W-3, they display very similar TGA curves with nearly identical Tds of ca. 410 oC (Figure 1a and Table 1), since their content of the IrIII phosphorescent units is nearly the same (ca. 10 wt%). However, P-W-1, P-W-2 and P-W-3 even possess higher content of IrIII phosphorescent units than P-B-4 (ca. 8 wt%). Hence, it is reasonable that P-W-1, P-W-2 and P-W-3 exhibit even lower Tds than P-B-4, possessing the lowest Td among the blue phosphorescent polymers. DSC traces of all the phosphorescent polymers indicate their high glass transition temperatures (Tg) above 200 °C with no crystallization and melting peaks (Figure 1b and Table 1). Clearly, all the phosphorescent polymers show similar Tg temperature (Figure 1b). So, the glass transition processes should be induced by organic backbones of the phosphorescent polymers rather than the phosphorescent units due to their low content. The high thermal stability and amorphous nature of the phosphorescent polymers are highly desirable for their EL applications, particularly in the devices fabricated by solution process.

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(a) P-B-1 P-B-2 P-B-3 P-B-4

20%

P-W-1 P-W-2 P-W-3 100

200

300

400

500

600

Temperature (o C)

(b) P-B-1 P-B-2 P-B-3 P-B-4

Exothermic

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Weight retentive ratio (%)


P-W-1 P-W-2 P-W-3

100

150

200

Temperature ( oC)

250

300

Figure 1. (a) TGA and (b) DSC curves of the phosphorescent polymers.

The UV/vis absorption spectra of both blue and white phosphorescent polymers have been measured in CH2Cl2 solution at 298 K (Figure 2). The absorption spectra of these phosphorescent polymers feature the major absorption bands at 248, 270, 300, 335 and 350 nm to the π−π* transitions in both carbazole and fluorene units of the polymer backbone (Figure 2 and Table 1). However, the low-energy metal-to-ligand charge transfer (MLCT) absorption bands (ca. 379, 415, 457 nm for M-IrB and 435, 455, 498 nm for M-IrO in Figure S1) from the IrIII phosphorescent units cannot be detected properly due their low content of in the polymer 10


Page 11 of 47

backbones (Figure 2). Hence, the absorption spectra of both blue and white phosphorescent polymers exhibit great similarity to that of P-Org (Figure 2). (a) P-B-1 P-B-2 P-B-3 P-B-4 P-Org

0.8 0.6

(b) P-W-1 P-W-2 P-W-3 P-Org

1.0

Absorption (a.u.)

1.0

Absorption (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.4 0.2 0.0

0.8 0.6 0.4 0.2 0.0

250

300

350

400

450

500

250

300

Wavelength (nm)

350

400

450

500

Wavelength (nm)

Figure 2. UV/vis absorption spectra of the polymers in CH2Cl2 at 298 K. (a) Blue phosphorescent polymers and model polymer P-Org and (b) White phosphorescent polymers and model polymer P-Org

Table 1. Photophysical and thermal data of these phosphorescent polymers and their model polymer. Compound

Absorption (298 K) λabs (nm) a

P-B-1

246, 258, 270, 300, 336, 355

Emission λem (nm) 298 K Solution Film 375, 474, 497 371, 467, 495

τ (µs) b Film 0.25 (474 nm)

Td/Tg (oC) c 457/215

P-B-2

247, 257, 269, 300, 336, 355

371, 467, 495

375, 474, 497

0.24 (474 nm)

449/218

P-B-3

248, 258, 268, 300, 336, 355

371, 467, 495

474, 497

0.24 (474 nm)

443/216

P-B-4

248, 258, 270, 299, 337, 355

372, 467, 495

474, 497

0.22 (474 nm)

439/213

P-W-1

249, 258, 270, 299, 335, 353

372, 468, 496

473, 498, 544, 585

0.23 (473 nm)

416/206

1.12 (544 nm) P-W-2

250, 258, 271, 300, 335, 352

373, 468, 496

473, 497, 544, 585

0.23 (473 nm)

415/205

0.79 (544 nm) P-W-3

249, 255, 271, 300, 335, 352

373, 467, 496

474, 498, 544, 585

0.25 (474 nm)

413/209

0.90 (544 nm) 0.005 (375 nm) 375/155 371 375 248, 258, 269, 300, 337, 355 P-Org a Measured in CH2Cl2. b Measured in spin-coated film and corresponding wavelength was shown in parentheses. The excitation wavelength was set at 355 nm for all the samples at 298 K. c Td is the decomposition temperature and Tg is the glass transition temperature.

On the contrary, the PL spectra recorded in solution at 298 K displayed two main emission 11



bands centered in both high and low energy regions (Figures 3a and 3c). The strong emission bands with high energy should represent the fluorescence from the organic polymer backbones contrast with that of P-Org (Figure S2) and their nanosecond order lifetimes (Table 1). The inefficient energy-transfer process from polymer backbone host to the phosphorescent units has been indicated by their fluorescence-dominated PL spectra. It can be noted that the intensity of phosphorescence has been enhanced with increase the content of blue phosphorescent units from P-B-1 to P-B-4 (Figure 3a). For P-W-1, P-W-2 and P-W-3, no detectable phosphorescent bands from M-IrO are shown in their solutions due to its extremely low content less than 1.0 wt% in the polymer backbones (Figure 3c). However, the weak emission bands from blue phosphorescent unit can be observed (Figure 3c). Clearly, P-W-1, P-W-2 and P-W-3 show the weak phosphorescent signals with almost same intensity (Figure 3c), owing to their almost identical content of the blue phosphorescent unit according to the feeding ratio of different monomers in the preparation of P-W-1, P-W-2 and P-W-3.

0.8 0.6 0.4 0.2

(b) P-B-1 P-B-2 P-B-3 P-B-4

1.0

PL intensity (a.u.)

(a) P-B-1 P-B-2 P-B-3 P-B-4

1.0

PL intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.8 0.6 0.4 0.2 0.0

0.0 350

400

450

500

550

600

350

650

400

450

500

550

Wavelength (nm)

Wavelength (nm)

12


600

650

(c) P-W-1 P-W-2 P-W-3

1.0

PL intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.8 0.6 0.4 0.2

(d) P-W-1 P-W-2 P-W-3

1.0

PL intensity (a.u.)

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0.0

0.8 0.6 0.4 0.2 0.0

350

400

450

500

550

600

650

400

450

Wavelength (nm)

500

550

600

650

700

Wavelength (nm)

Figure 3. PL spectra for the phosphorescent polymers in CH2Cl2 at 298 K. (a) Solutions of blue phosphorescent polymers, (b) Films of blue phosphorescent polymers, (c) Solutions of white phosphorescent polymers and (d) Films of white phosphorescent polymers

In contrast, the PL spectra of thin films of the phosphorescent polymers exclusively emit intense phosphorescent signal originating from the iridium moieties of each corresponding polymer although the emission from the polymer backbone is concomitantly observed in the polymers with low content of phosphorescent unit (P-B-1 and P-B-2) (Figure 3b). The blue phosphorescent polymers can exhibit the highest phosphorescent band at ca. 474 nm (Figure 3b), identical to monomer M-IrB (ca. 474 nm, Figure S3) doped in P-Org. It indicates that no undesired bathochromic effect in emission wavelength of the blue phosphorescent polymers can be induced by the polymerization process. In the white phosphorescent polymers P-W-1, P-W-2 and P-W-3 with complimentary colors, the emission bands from both blue and orange phosphorescent unit can be clearly observed (Figure 3d). Nearly no fluorescence from the organic backbone can be detected in P-W-1, P-W-2 and P-W-3. The good overlapping between the absorption spectra of the phosphorescent units and the emission spectrum of P-Org should also promote the energy-transfer processes from the backbones of organic polymers to the phosphorescent units (Figure 4). All these results indicate the efficient energy-transfer processes from polymer backbones to the phosphorescent units in the rigid film matrix, rendering these 13



polymers suitable for use as emitters in phosphorescent OLEDs (PhOLEDs).

Absorption (a.u.)

1.0

M-IrB M-IrO P-Org

0.8

1.0 0.8

0.6

0.6

0.4

0.4

0.2

0.2

0.0 250

PL intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.0 300

350

400

450

500

550

Wavelength (nm) Figure 4. UV/vis spectra for the phosphorescent monomer and PL spectrum for the model polymer in CH2Cl2 at 298 K.

From the PL spectra of P-Org measured at 77 K (Figure 5), the ET of these phosphorescent polymer backbones can be obtained as ca. 2.83 eV, which is greater than the ET of blue and orange phosphorescent units (ca. 2.62 eV and 2.28 eV, respectively). This can guarantee the efficient energy-transfer process from the backbones of the polymer to the phosphorescent units, effectively avoiding undesired back energy-transfer and hence enhancing their EL performances. The ET of ca. 2.83 eV for the model polymer P-Org is nearly the same to that of FlbCz (ca. 2.86 eV), regarded as the repeating unit of the backbones of these phosphorescent polymers. It means that polymerization has not lowered the ET of the novel polymer backbones substantially owing to the unique arrangement between the carbzole and fluorene units to effectively break the conjugation of polymer backbone. The high ET associated with the novel polymer backbones should indicate their great potential in developing high performance blue phosphorescent polymers as well as the white-emitting ones with blue phosphorescent units.

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O

O

1.0

PL intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


N

P-Org FlbCz

N

0.8

0.6

FlbCz

0.4

0.2 350

400

450

500

550

Wavelength (nm) Figure 5. PL spectra of model polymer P-Org and FlbCz in CH2Cl2 glass at 77 K.

Electrochemical Properties. Under a nitrogen flow, the cyclic voltammetry (CV) calibrated with ferrocene/ferrocenium (Fc/Fc+) redox couple as an internal reference has been employed to characterize the electrochemical properties of these phosphorescent polymers. The results are presented in Table 2. All the phosphorescent polymers display one detectable reversible anodic potential Ea (ca. 0.40 V), very similar to the organic model polymer P-Org. So, it can be concluded that the oxidation process should be induced by the backbones of these phosphorescent polymers. Considering the electronic features of these different units constructing the backbone of the polymer, the existence of electron-rich carbazole units can be safely assigned to the oxidation. However, the anodic potentials for the phosphorescent units in the polymer backbones cannot be observed properly for their low content. In the cathodic scan, all the phosphorescent polymers cannot exhibit detectable reduction process. Hence, the LUMO energy-levels of these phosphorescent polymers are calculated by the equation of ELUMO = Eg + EHOMO, in which the optical energy-gap is derived from their absorption onset. Clearly, the electrochemical properties of these phosphorescent polymers are very similar to that of the polymeric model P-Org (Table 2) and the redox signals of the IrIII phosphorescent units cannot 15



be recorded properly, which can be explained by the low content of the IrIII phosphorescent units in these phosphorescent polymers.

Table 2. Electrochemical properties for these phosphorescent polymers and their model polymer. Polymer Ea (V) a EHOMO (eV)b ELUMO (eV)c Eg (eV)d 0.39 -5.19 -1.81 3.38 P-B-1 0.38 -5.18 -1.80 3.38 P-B-2 0.39 -5.19 -1.81 3.38 P-B-3 0.37 -5.17 -1.81 3.36 P-B-4 0.38 -5.18 -1.82 3.36 P-W-1 0.39 -5.19 -1.83 3.36 P-W-2 0.39 -5.19 -1.83 3.36 P-W-3 0.38 -5.18 -1.79 3.39 P-Org a

Reversible. The value was set as E1/2.

equation HOMO = – (4.8 + Ea).

d

b

HOMO levels are calculated according to the

ELUMO = Eg + EHOMO.

d

Optical energy gap Eg was

determined by the absorption onset.

Electrophosphorescent OLEDs. For characterizing the EL capacity of these emissive polymers, OLEDs have been fabricated by convenient spin-coating approach. With the aim to show the quality of the polymer films obtained by spin-coating, their atomic force microscopy (AFM) images have been obtained (Figure 6). It seems that all these polymer films possess high quality by showing smooth surfaces with low root mean square roughness (RMS) less than 1.0 nm, which is quite desirable for furnishing high-performance devices.

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Figure 6. AFM images for the surfaces of the films spin-coated from the phosphorescent polymer solutions together with the RMS values. (a) P-B-1, (b) P-B-2, (c) P-B-3, (d) P-B-4, (e) P-W-1, (f) P-W-2 and (g) P-W-3 The devices using these phosphorescent polymers possess the configuration of ITO/PEDOT:PSS (40 nm)/polymer (30 nm)/TPBi (60 nm)/LiF (1 nm)/Al (100 nm) (Figure 7). In this device configuration, PEODT:PSS acts as the hole transporting layer (HTL), while TPBi serves the function of electron-transporting and hole-blocking because of its relatively low HOMO level. Table 3 summarizes the EL performance data of the blue electrophosphorescent OLEDs.

17



Page 18 of 47

Al (100 nm)

N

LiF (1 nm) TPBi (60 nm)

N

N

N

Emission layer (30 nm) PEDOT:PSS (40 nm)

N

ITO Glass

O

O

O

O

TPBi

S

+

S O

_

SO3H SO3

S

S O

N

+

O

n O

_

SO3H SO3

SO3H

Device Emission layer B1 B2 B3 B4 W1 W2 W3

P-B-1 P-B-2 P-B-3 P-B-4 P-W-1 P-W-2 P-W-3

n PEDOT:PSS

Figure 7. Structures of the solution-processed OLEDs based on these phosphorescent polymers as well as the functional materials employed.

Table 3. EL performance of the OLEDs using these blue phosphorescent polmers. Device

Dopant

Vturn-on

Luminance Lmax −2 a

ηext

ηL

ηp

λmax

(V)

(cd m )

(%)

(cd A )

(lm W )

(nm) d

2.14 (3.7) a 1.91 b 1.60 c 3.47 (3.8) 3.22 2.74 6.22 (3.8) 5.64 5.03 5.30 (3.3) 3.95 3.16

4.83 (3.7) 4.28 3.67 7.81 (3.8) 7.32 6.10 15.22 (3.8) 13.72 11.70 12.42 (3.3) 9.25 7.34

4.07 (3.7) 2.14 1.40 6.49 (3.8) 3.97 2.41 12.64 (3.8) 7.24 5.12 11.79 (3.3) 4.10 2.59

472 (0.19, 0.38)

B1

P-B-1 (2.0 wt %)

4.6

1227 (15.6)

B2

P-B-2 (4.0 wt %)

3.8

2675 (15.7)

B3

P-B-3 (6.0 wt %)

3.8

3025 (15.6)

B4

P-B-4 (8.0 wt %)

4.7

1813 (17.0)

−1

a

−1

472 (0.19, 0.38) 472 (0.19, 0.38) 472 (0.19, 0.38)

Maximum data. Numbers in parentheses are the voltages at which the data can be obtained. b Data at 10 cd m−2. Data at 100 cd m−2. d Data obtained at 6 V, CIE coordinates (x, y) in parentheses.

18


c

Page 19 of 47

1.0

EL intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4V 5V 6V 7V 8V 9V 10 V 11 V

0.8 0.6 0.4 0.2 0.0 400

500

600

700

Wavelength (nm) Figure 8. EL spectra of the optimized blue-emitting Device B3 at different voltages.

After applying a proper voltage, the OLEDs with the blue phosphorescent polymers as emitters exhibited intense sky-blue electroluminescence. As depicted in Figure 8 and Figure S4, the EL spectral profile of the blue-emitting device is nearly identical to the PL spectrum of the corresponding polymer in solid film, indicating that the EL emission indeed originates from the triplet excited states of the IrIII units. Additionally, no residual emission from the polymer backbone host can be obviously observed in these blue-emitting devices (Figure 8 and S4), implying the highly efficient forward energy transfer from the host excitons to the phosphorescent units and effective confinement of the excitons on the IrIII units in these blue phosphorescent polymers to guarantee their high EL efficiencies. Importantly, these blue-emitting OLEDs can show very stable EL spectra in wide range of dirving voltage (Figure 8 and Figure S4). The current density–voltage–luminance (J−V−L) characteristics and EL efficiency–luminance curves for these blue-emitting OLEDs are shown in Figure 9 and Figure S5. All the blue-emitting OLEDs show the turn-on voltages of less than 5.0 V (Table 3). Among all the blue 19



phosphoescent polymers with different content of IrIII units, the maximum EL ability has been achieved by P-B-3 with ca. 6.0 -wt% blue phosphorescent unit (Table 3). The optimized device (Device B3) with P-B-3 as emitter can exhibit the best EL performance with a turn-on voltage (Vturn-on) of 3.8 V, and a maximum luminance (Lmax) of 3025 cd m−2 at 15.6 V, a peak luminance efficiency (ηL) of 15.22 cd A−1, corresponding to a peak power efficiency (ηP) of 12.64 lm W−1 and a peak external quantum efficiency (ηext) of 6.22% (Table 3). Even at luminance of 100 cd m-2, device B3 can still maintain high EL efficiencies of 11.70 cd A−1, 5.12 lm W−1 and 5.03% (Table 3 and Figure 10) Obviously, the peak ηL of 15.22 cd A−1 for device B3 should represent the state-of-the-art highly efficient blue phosphorescent OLEDs ever achieved by blue phosphorescent polymers. In addition, the device B4 with P-B-4 as emitter can also exhibit remarkable EL performances with ηL of 12.42 cd A−1, ηP of 11.79 lm W−1 and ηext of 5.30%

-2

Current density (mA cm )

(Table 3 and Figure S6). 200 1000 160 120

100

80 10 40 0 4

8

12

16

Voltage (V) Figure 9. J−V−L characters of the optimized blue-emitting device B3.

20


1

Luminance (cd m-2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 47

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10 1

-1

-1

ηL /η P ( cd A / lm W )

10

ηext (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

0.1

ηext ηL ηP

0.1 1

10

100

1000

0.01

-2

Luminance (cd m ) Figure 10. Relationship between the EL efficiency and luminance for the optimized device B3.

With the same device configuration, WOLEDs have also been constructed with P-W-1, P-W-2 and P-W-3 as emitters. The obtained EL data for the WOLEDs are shown in Table 4. In the EL spectra of the WOLEDs (Figure 11), the EL bands from both blue and orange phosphorescent units can be seen clearly. No EL signal from the polymer backbone can be properly detected (Figure 11), suggesting that the efficient energy-transfer from the backbone of the polymers acting as host material to the phosphorescent units. Owing to the low ratio for blue to orange phosphorescent units (B/O ratio) ca. 15 : 1 in P-W-1, device W1 shows orange-dominated EL spectra (Figure 11a). Clearly, the energy-transfer from blue phosphorescent units to orange ones also accounts for the unbalanced white EL spectra in device W1. So, device W1 shows EL spectra with low color rendering index (CRI) of ca. 45 at 10 V. Through increasing B/O ratio of ca. 20 : 1 in P-W-2 and then ca. 30 : 1 in P-W-3, the blue EL band can be effectively enhanced successively. Hence, more balanced white EL spectra can be achieved in devices W2 and W3 (Figure 11b and 11c) and higher CRI has been fulfilled (ca. 53 for W2 and 58 for W3 at 10 V). Importantly, all the solution-processed WOLEDs can exhibit 21



Page 22 of 47

very stable CIE coordinates in wide range of driving voltage from 4 V to 16 V, representing a critical feature required by practical light sources. As new candidates of new light source, CIE coordinates associated with the EL spectra of WOLEDs should only drift ca. 0.01 or less for both the x- and y-values in wide driving voltage range. For device W1, the drifting value of its CIE coordinates is (∆x = 0.006, ∆y = 0.004) from 4 V to 16 V. And those for W2 and W3 are (∆x = 0.014, ∆y = 0.010) and (∆x = 0.009, ∆y = 0.006), respectively, representing exceptional stability of CIE coordinates ever achieved in solution-processed WOLEDs. These very stable CIE coordinates of WOLEDs should indicate their potential for developing simple WOLEDs for practical application. Table 4. EL performance of the solution-processed WOLEDs. Device

Dopant

Vturn-on

Luminance Lmax

ηext

ηL

ηp

λmax

(V)

(cd m−2) a

(%)

(cd A−1)

(lm W−1)

(nm) d

4.25 (4.5) a 4.04 b 3.83 c 4.10 (4.5) 3.86 3.56 3.82 (3.8) 3.68 3.46

14.03 (4.5) 13.33 12.65 12.34 (4.5) 11.39 10.51 10.40 (3.8) 10.02 9.45

10.91 (4.5) 6.09 4.55 9.59 (4.5) 5.12 3.17 7.66 (3.8) 4.91 3.34

472, 500, 544, 585 (0.394, 0.515)

W1

P-W-1

4.5

7525 (19.2)

W2

P-W-2

4.5

7489 (20.6)

W3

P-W-3

4.3

7151 (18.9)

a

472, 500, 544, 585 (0.338, 0.471) 472, 500, 544, 585 (0.296, 0.428)

Maximum data. Numbers in parentheses are the voltages at which the data can be obtained. b Data at 10 cd m−2. Data at 100 cd m−2. d Data obtained at 6 V, CIE coordinates (x, y) in parentheses.

22


c

Page 23 of 47

EL intensity (a.u.)

1.0

(a) 4 V (0.391, 0.514) 6 V (0.393, 0.515) 8 V (0.394, 0.515) 10 V (0.395, 0.516) 12 V (0.396, 0.516) 14 V (0.397, 0.516) 16 V (0.395, 0.512)

0.8 0.6 0.4 0.2 0.0 400

500

600

700

800

Wavelength (nm)

EL intensity (a.u.)

1.0

(b) 4 V (0.332, 0.468) 6 V (0.336, 0.470) 8 V (0.338, 0.471) 10 V (0.341, 0.473) 12 V (0.344, 0.475) 14 V (0.345, 0.477) 16 V (0.346, 0.478)

0.8 0.6 0.4 0.2 0.0 400

500

600

700

800

Wavelength (nm) 1.0

EL intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(c) 4 V (0.291, 0.424) 6 V (0.293, 0.426) 8 V (0.296, 0.428) 10 V (0.298, 0.429) 12 V (0.300, 0.430) 14 V (0.299, 0.430) 16 V (0.295, 0.426)

0.8 0.6 0.4 0.2 0.0 400

500

600

700

800

Wavelength (nm) Figure 11. EL spectra for the WOLEDs at different driving voltages and CIE coordinates are shown in parentheses. (a) W1, (b) W2 and (c) W3

23



10000

Device W1 Device W2 Device W3

-2

Current density ( mA cm )

120 100

Luminance (cd m-2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 47

1000

80 100

60 40

10

20 1 0 4

8

12

16

20

Voltage (V) Figure 12. J−V−L characters for the solution-processed WOLEDs.

All the solution-processed WOLED can be turned-on at ca. 4.5 V with Lmax higher than 7000 cd m−2 (Table 4 and Figure 12). Obviously, with increasing B/O ratio from P-W-1 (ca. 15 : 1) to P-W-2 (ca. 20 : 1) and then to P-W-3 (ca. 30 : 1), the EL efficiencies of the WOLEDs decrease, for example 14.03 cd A−1 for W1, 12.34 cd A−1 for W2 and 10.40 cd A−1 for W3, respectively (Table 4 and Figure 12). Clearly, the EL performances for P-W-1, P-W-2 and P-W-3 are decided by both blue and orange phosphorescent units rather than the blue-emitting ones. It has been well accepted the EL efficiencies of WOLEDs are typically up to the blue emitter if the long-wavelength emitters are excited by the cascade energy-transfer from blue emitter. Hence, based on these results, the orange phosphorescent units in these polymers should be mainly excited by direct charge-carrier trapping mechanism despite that cascade energy-transfer excitation

cannot

be

totally

excluded.

The

electron-donating

carbazole

unit

and

electron-withdrawing pyridyl moiety should definitely favor the direct charge-carrier trapping mechanism for both blue and orange phosphorescent units in these polymers. This excitation mechanism might have guaranteed the stable EL spectra in these solution-processed WOLEDs. Taking both EL efficiencies and white EL spectral pattern into consideration, devices W2 and 24


Page 25 of 47

W3 can show more optimized EL performances compared with device W1, especially for W2 (Table 4 and Figure 12). Device W2 can be turned on at ca. 4.5 V and show Lmax of 7489 cd m−2 at 20.6 V, a peak ηL of 12.34 cd A−1, corresponding to a peak ηP of 9.59 lm W−1 and a peak ηext of 4.10% (Table 4 and Figure 13b). In addition, device W3 can also exhbit good EL performances with ηL of 10.40 cd A−1, ηP of 7.66 lm W−1 and ηext of 3.82%. 10

10 1

-1

-1

η L /η P (cd A / lm W )

(a)

ηext (%)

1

0.1

ηext ηL ηP

0.1 1

10

100

-2

1000

Luminance (cd m )

10

(b) 10

1

-1

-1

η L /η P (cd A / lm W )

0.01 10000

ηext (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

0.1

ηext ηL ηP

0.1 1

10

100

1000 -2

Luminance (cd m )

25


0.01 10000


10

10 1

Device W3

-1

-1

ηL /η P (cd A / lm W )

(c)

ηext (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 47

1

0.1

ηext ηL ηP

0.1 1

10

100

1000

0.01 10000

-2

Luminance (cd m )

Figure 13. Relationship between the EL efficiency and luminance for the solution-processed WOLEDs. (a) W1, (b) W2 and (c) W3

Owing to the convenience for device fabrication with simple solution process, both blue and white phosphorescent polymers have been prepared to make OLEDs. Blue phosphorescent polymers have been developed through employing fluorinated poly(arylene ether phosphine oxide) as backbone attached with FIrpic-derived phosphorescent unit.59 These novel blue phosphorescent polymers can show high EL efficiency of 19.4 cd A−1, 10.0 lm W-1 and 9.0%. Another series of blue phosphorescent polymers with polynorbornene backbone attached with both 9,9′-(1,3-phenylene)bis-9H-carbazole (mCP) and FIrpic units can also show attractive EL performances with maximum ηp of 12.9 lm W-1 and 8.8%.44 Except the higher EL efficiencies aforementioned, blue phosphorescent polymers typically show ηext less than 5% and ηL less than 10 cd A−1. 60 For the white phosphorescent polymers, the state-of-the-art EL efficiency18.4 cd A-1 (8.5 lm W-1 and 7.1%) has been achieved in polymers with fluorinated poly(arylene ether phosphine oxide) as backbone. In addition, WOLEDs based on phosphorescent supramolecular polymers can achieve nice EL efficiencies of 2.17% and 3.91 cd A-1.51 Compared with these 26


Page 27 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


attractive EL performances aforementioned, the EL efficiencies of 15.22 cd A−1, 12.64 lm W−1 and 6.22% achived by these novel blue phosphorescent polymers together with 12.34 cd A−1, 9.59 lm W−1 and 4.10% furnished by white phosphorescent analoges should difinitley set these polymeric emitters among the most efficieny phosphorescent polymers. All these EL data can clearly show the importance of the concerned molecular design conception, which can provide a valuable guidance for synthesis new phosphorescent polymers with high EL efficiency.

CONCLUSION In conclusion, in order to restrain undesired back energy-transfer in phosphorescent polymers, novel polymer backbone has been successfully developed through perpendicular arranging the building blocks to effectively break conjugation and furnish high triplet energy level (ET) of ca. 2.83 eV. Based on this novel polymer backbone with high ET, both blue and white phosphorescent polymers have been developed. Owing to the advantages associated with the new polymer backbone, the blue phosphorescent polymers can show state-of-the-art EL performances with maximum luminance efficiency (ηL) of 15.22 cd A−1, corresponding to external quantum efficiency (ηext) of 6.22% and power efficiency (ηP) of 12.64 lm W−1 with the CIE coordinates of (0.19, 0.38). In addition, white phosphorescent polymers with B-O complementary colors based on this novel polymer backbone have been obtained as well to furnish encouraging EL efficiencies of 12.34 cd A−1, 9.59 lm W−1 and 4.10% together with exceptionally stable CIE cooridicates. All these promising EL results achieved by these novel phosphorescent polymers will provide very important information about the critical role played by the novel backbone in optimizing the electroluminescence ability of these phosphorescent polymers. Furthermore, the concerned phosphorescent polymers should represent new platform 27



for developing highly efficient polymeric phosphorescent emitters.

EXPERIMENTAL SECTION General Information. All commercially available starting materials were used directly with no further purification. The solvents were carefully dried prior to use. Thin-layer chromatography (TLC) plates from Merck & Co. were used to monitore all the reactions. Preparative TLC and flash column chromatography were made from silica gel bought from Shenghai Qingdao (300-400 mesh). 1H, 13C and 19F NMR spectra were recorded in CDCl3 on a Bruker Avance 400 MHz spectrometer and chemical shifts were referenced to the residual solvent peak at δ 7.26 ppm and 77.0 ppm for 1H and 13C, respectively. Elemental analyses were performed on a Flash EA 1112 elemental analyzer. The thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) data were collected on a NETZSCH STA 409C instrument and a NETZSCH DSC 200 PC unit, respectively. UV-vis absorption spectra were obtained at room temperature using a Shimadzu UV-2250 spectrophotometer. FLSP920 fluorescence spectrophotometer of Edinburgh Instruments Ltd was empolyed to record the emission spectra and lifetimes through the software package provided by Edinburgh Instruments. Cyclic voltammetry was performed using a Princeton Applied Research model 2273A potentiostat at 100 mV s-1. All experiments were carried out in a three-electrode compartment cell. The counter electrode is a Pt-sheet, working electrode is glassy carbon and the reference electrode is Ag/AgCl, 0.1 M [nBu4N]BF4 solution in acetonitrile was used as the supporting electrolyte. Finnigan MAT SSQ710 spectroscopy was used to obtain the fast atom bombardment (FAB) mass spectra. The surface morphology for the doped films is obtained on the Dimension 3000 Atomic Force Microscope, Digital Instrument. 28


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Synthesis. Synthetic details for the critical intermediate compounds 6-hydroxymethylpicolinate (PicMe), 1-(2-bromoethoxy)-4-iodobenzene (IPhOBr) 9-(4-(hexyloxy)phenyl)-9H-carbazole (CzPhOC6) have been provided in SI. 4-(9H-Carbozol-9-yl)phenylboronic acid (CzPhB) was purchased from Acros. The IrIII µ-chlorobridged dimmers Ir[dFppy]2Cl2, Ir[PyFl]2Cl2 and the organic ligand PyFl were prepared according literature method.57-58 PicOPhI. To a round-bottom-flask containing PicMe (0.30 g, 2.00 mmol), IPhOBr (0.65 g, 2.00 mmol), K2CO3 (2.20 g, 16.00 mmol) and KI (0.33 g, 2.00 mmol), Acetone (30 mL) was added and the reaction mixture was stirred at 60 oC for 24 h. After solvent was removed at reduced pressure, water (100 mL) was added to the reaction mixture, which was extracted by CH2Cl2 (3 × 30 mL). The organic layer was dried over anhydrous Na2SO4. After solvent removing, the residue was purified by column chromatography over silica using CH2Cl2/hexane (4:1, v:v) as eluent. The product was obtained as white solid (0.54 g, 68%). 1H NMR (400 MHz, CDCl3, δ): 7.74-7.68 (m, 2H), 7.56 (d, J =8.8 Hz, 2H), 6.99 (dd, J = 7.6, 1.6 Hz, 1H), 6.75 (d, J = 9.2 Hz, 1H), 4.77 (t, J = 4.4, 2H, CH2), 4.31(J = 4.8, 2H, CH2); 13C NMR (100 MHz, CDCl3, δ): 165.54, 163.07, 158.60, 145.28, 139.28, 138.24, 119.01, 117.12, 115.57, 83.07, 66.38, 64.27, 52.65; FAB-MS (m/z): 399 [M] +; Anal. Calcd. for C15H14INO4: C, 45.13; H, 3.54; N, 3.51; found: C, 44.95; H, 3.38; N, 3.42%. CzOPicMe. Under a nitrogen atmosphere, CzPhB (0.32 g, 1.10 mmol), PicOPhI (0.40 g, 1.00 mmol) and Pd(PPh3)4 (0.05 g, 0.043 mmol) were added to a mixture of degassed toluene (20 mL) and 2M Na2CO3 (3 mL). The reaction mixture was heated to 90oC and stirred for 6 h. After cooling to room temperature, the mixture was extracted by CH2Cl2 (3 × 30 mL). The organic layer was dried over anhydrous Na2SO4. The crude product was purified by column chromatography over silica using CH2Cl2/hexane (2:1, v:v) as an eluent. White solid was 29



obtained (0.42 g, 81%). 1H NMR (400 MHz, CDCl3, δ): 8.17 (m, J = 8.0 Hz, 2H), 7.79-7.04 (m, 4H), 7.62 (t, J = 8.8 Hz, 4H), 7.49-7.41 (m, 4H), 7.30 (t, J = 7.2, 2H), 7.11(d, J = 8.8, 2H), 7.03 (dd, J = 7.6, 1.2, 1H), 4.84 (t, J = 4.8, 2H, CH2), 4.44 (t, J = 4.8, 2H, CH2), 3.99 (s, 3H, OMe); 13

C NMR (100 MHz, CDCl3, δ): 165.60, 163.16, 158.55, 145.28, 140.88, 139.87, 139.25,

136.27, 133.08, 128.18, 128.00, 127.31, 125.91, 123.35, 120.28, 119.89, 118.99, 115.63, 115.15, 109.82, 66.43, 64.49, 52.66; FAB-MS (m/z): 514 [M] +; Anal. Calcd. for C33H26N2O4: C, 77.03; H, 5.09; N, 5.44; found: C, 76.84; H, 5.21; N, 5.29%. CzOPicOH. CzOPicMe (0.30 g, 0.58 mmol) and NaOH (0.09 g, 2.25 mmol) were dissolved in the mixture of MeOH (5 mL) and THF (5 mL) and the mixture was stirred at room temperature overnight. Then, water (10 mL) was added and the pH value of the mixture was adjusted to ca. 6.0 with concentrate HCl. After extracted with EtOAc (3 × 15 mL), the combined organic layer was dried over anhydrous Na2SO4. After removing solvent, the obtained white solids were washed with hexane (3 × 15 mL). The product was obtained in high yield (0.25 g, 86%). 1H NMR (400 MHz, DMSO-d6, δ): 8.30 (d, J = 8.0 Hz, 2H), 7.97-7.92 (m, 3H), 7.80-7.71 (m, 5H), 7.49 (d, J = 3.88 Hz, 4H), 7.36-7.32 (m, 2H), 7.22-7.17 (m, 3H), 4.76-4.73 (m, 2H), 4.48-4.71 (m, 2H); 13C NMR (100 MHz, DMSO-d6, δ): 171.04, 167.94, 163.42, 162.15, 151.07, 145.60, 145.32, 144.14, 140.70, 137.01, 133.45, 132.99, 132.26, 131.29, 127.96, 125.78, 124.81, 123.88, 121.78, 120.64, 114.92, 69.52, 69.38, 57.69; FAB-MS (m/z): 500 [M] +; Anal. Calcd. for C32H24N2O4: C, 76.78; H, 4.83; N, 5.60; found: C, 76.62; H, 4.68; N, 5.46%. M-IrB. Under a nitrogen atmosphere, CzOPicOH (0.02 g, 0.04 mmol), Ir[dFppy]2Cl2 (0.023 g, 0.018 mmol) and Na2CO3 (0.19 g, 1.80 mmol) were dissolved in 2-ethoxyethanol (5 mL). The reaction mixture was heated to 80 oC and stirred for 2 h. Then, saturated NaCl solution (15 mL) was added. The colored precipitate was collected by filtration then purified by column 30


Page 30 of 47

Page 31 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


chromatography over silica using EtOAc/MeOH (12:1, v:v) as an eluent. Pale yellow solid (0.036 g, 93%) was obtained as product. 1H NMR (400 MHz, CDCl3, δ): 8.64 (d, J = 5.6 Hz, 1H), 8.24 (d, J = 8.8 Hz, 1H), 8.09 (d, J = 8.4 Hz, 1H), 8.06 (d, J = 7.2 Hz, 1H), 7.96 (t, J = 7.6, 1H), 7.70-7.46 (m, 17H), 7.08 (t, J = 6.4 Hz, 1H), 7.02 (d, J = 8.4 Hz, 1H), 6.79 (t, J = 6.4 Hz, 1H), 6.73 (dd, J = 8.8, 2.8 Hz, 2H), 6.36 (td, J = 10.6, 2.0 Hz, 1H), 6.23 (td, J = 10.6, 2.0 Hz, 1H), 5.70 (dd, J = 9.2, 2.4 Hz, 1H), 5.38 (dd, J = 8.8, 2.4 Hz, 1H), 4.17-4.12 (m, 1H), 4.04-3.99 (m, 1H), 3.73-3.68 (m, 1H), 3.58-3.53 (m, 1H); 13C NMR (100 MHz, CDCl3, δ): 173.06, 165.35, 165.06, 163.99, 161.43, 160.63, 159.57, 155.74, 151.18, 150.15, 148.85, 148.20, 143.06, 141.62, 138.47, 138.00, 137.93, 133.94, 133.28, 132.24, 132.05, 131.96, 128.59, 128.47, 127.66, 125.28, 124.20, 123.34, 123.15, 122.46, 122.22, 121.85, 121.74, 114.31, 114.18, 113.93, 113.48, 110.01, 107.35, 104.42, 100.88, 98.39, 98.12, 97.85, 96.32, 96.06, 67.14, 65.06;

19

F NMR (376 MHz,

CDCl3, δ): -107.86 (d, J = 11.3 Hz, 1F), -108.55 (d, J = 7.5 Hz, 1F), -110.54 (d, J = 7.5 Hz, 1F), -110.74 (d, J = 7.5 Hz, 1F); FAB-MS (m/z): 1072 [M] +; Anal. Calcd. for C54H35F4IrN4O4: C, 60.50; H, 3.29; N, 5.23; found: C, 60.39; H, 3.35; N, 5.15%. CzPicMe. Under a nitrogen atmosphere, methyl 5-bromomethylpicolinate (0.27 g, 1.27 mmol), CzPhB (0.44 g, 1.50 mmol) and Pd(PPh3)4 (0.073 g, 0.064 mmol) were added to 10 mL degassed toluene (10 mL) and 2M Na2CO3 (3 mL). The reaction mixture was heated to 110oC and stirred for 16 h. After cooling to room temperature, CH2Cl2 (20 mL) was added and the mixture was washed with water (3 × 30 mL). The organic phase was dried over anhydrous Na2SO4. The crude product was purified by column chromatography over silica using CH2Cl2/EtOAc (30:1, v:v) as eluent. The product was obtained as white solid (0.43 g, 89%). 1H NMR (400 MHz, CDCl3, δ): 9.08 (d, J = 1.6 Hz, 1H), 8.28 (d, J = 8.0 Hz, 1H), 8.17 (d, J = 8.0 Hz, 2H), 8.13 (dd, J = 8.0, 2.0 Hz, 1H), 7.87 (d, J = 8.4 Hz, 2H), 7.74 (d, J = 8.4 Hz, 2H), 31



7.42-7.50 (m, 4H), 7.32 (t, J = 8.0 Hz, 2H), 4.07 (s, 1H, OCH3); 13C NMR (100 MHz, CDCl3, δ): 165.55 (C=O), 148.21, 146.72, 140.53, 138.88, 138.56, 135.44, 135.10, 128.83, 127.67, 126.08, 125.33, 123.57, 120.41, 120.28, 109.67, 53.00; FAB-MS (m/z): 378 [M] +; Anal. Calcd. for C25H18N2O2: C, 79.35; H, 4.79; N, 7.40; found: C, 79.26; H, 4.88; N, 7.29%. CzPicOH. CzPicMe (0.20 g, 0.53 mmol) and NaOH (0.09 g, 2.25 mmol) were dissolved in the mixture of MeOH (5 mL) and THF (5 mL) and the mixture was stirred at room temperature overnight. Then, water (10 mL) was added and the pH value of the mixture was adjusted to ca. 6.0 with concentrate HCl. After extracted with EtOAc (3 × 15 mL), the combined organic layer was dried over anhydrous Na2SO4. After removing solvent, the obtained white solid were washed with hexane (3 × 15 mL). The product was obtained in high yield (0.16 g, 83%). 1H NMR (400 MHz, CDCl3, δ): 8.97 (d, J = 2.0 Hz, 1H), 8.37 (d, J = 8.0 Hz, 1H), 8.24 (dd, J = 8.4, 2.4 Hz, 1H), 8.17 (d, J = 8.4 Hz, 2H), 7.88 (d, J = 8.4 Hz, 2H), 7.77 (d, J = 8.4 Hz, 2H), 7.43-7.50 (m, 4H), 7.33 (td, J = 7.0, 1.2 Hz, 2H);

13

C NMR (100 MHz, DMSO, δ): 166.84,

147.79, 140.41, 137.80, 137.22, 135.79, 135.54, 134.21, 129.38, 127.77, 126.85, 125.08, 123.36, 121.08, 120.76, 110.19; FAB-MS (m/z): 364 [M] +; Anal. Calcd. for C24H16N2O2: C, 79.11; H, 4.43; N, 7.69; found: C, 79.02; H, 4.28; N, 7.53%. M-IrO. Under a nitrogen atmosphere, CzOPicOH (0.053 g, 0.15 mmol), Ir[PyFl]2Cl2 (0.11 g, 0.067 mmol) and Na2CO3 (0.071 g, 0.67 mmol) were dissolved in 2-ethoxyethanol (5 mL). The reaction mixture was heated to 80 oC and stirred for 2 h. Then, saturated NaCl solution (15 mL) was added. The colored precipitate was collected by filtration then purified by column chromatography over silica using EtOAc/CH2Cl2 (1:3, v:v) as eluent. The product was obtained as orange solid (0.11 g, 75%).1HNMR (400 MHz, CDCl3, δ): 8.93 (d, J = 5.6 Hz, 1H), 8.44 (d, J = 8.0 Hz, 1H), 8.18-8.10 (m, 4H), 8.03 (d, J = 8.0 Hz, 1H), 7.99 (d, J = 7.6 Hz, 1H), 7.80 (q, J = 32


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7.2 Hz, 2H), 7.68 (d, J = 5.6 Hz, 1H), 7.63 (s, 1H), 7.59 (s, 1H), 7.47 (s, 4H), 7.36-7.16 (m, 15H), 6.98 (t, J = 6.8 Hz, 1H) , 6.81 (s, 1H), 6.21 (s, 1H), 2.08-1.90 (m, 8H), 0.37-0.23 (m, 12H); 13

CNMR (100 MHz, CDCl3, δ): 151.04, 150.98, 150.81, 149.34, 148.31, 147.80, 146.23, 146.18,

143.56, 143.45, 143.17, 142.91, 142.87, 142.78, 140.99, 140.28, 139.54, 138.75, 136.98, 136.93, 135.13, 133.90, 128.34, 128.22, 127.52, 127.28, 126.76, 126.39, 126.23, 126.02, 123.56, 123.50, 123.27, 122.79, 122.75, 121.78, 121.45, 120.41, 120.33, 119.83, 119.61, 119.13, 118.81, 118.67, 118.55, 109.47, 55.42, 55.27, 33.06, 32.88, 32.73, 32.65, 8.86, 8.74, 8.66; FAB-MS (m/z): 1152 [M] +; Anal. Calcd. for C68H55IrN4O2: C, 70.87; H, 4.81; N, 4.86; found: C, 70.69; H, 4.67; N, 4.73%. FlbCz. Under a nitrogen atmosphere, Fluorenone (0.016 g, 0.0889 mmol), CzPhOC6 (0.067 g, 0.1955 mmol) were dissolved in CH2Cl2 (1 mL). Then, Eaton’s Reagent (P2O5, 7.5 wt % in MeSO3H) (0.05 mL) was added to the reaction mixture and stirred at 100 oC for 6 h. After cooling to room temperature, CH2Cl2 (10 mL) and 2M Na2CO3 (5 mL) was added to quench the reaction. The mixture was extracted with CH2Cl2 (3 × 10 mL) and the organic phase was dried over anhydrous Na2SO4. Then the solvent was removed and the residue was collected by filtration then purified by column chromatography over silica using hexane/CH2Cl2 (7:1, v:v) as an eluent. White solid (0.05 g, 65%) was obtained. 1H NMR (400 MHz, CDCl3, δ): 8.00 (d, J = 1.6 Hz, 2H), 7.94 (d, J = 8.0 Hz, 2H), 7.83 (d, J = 7.6 Hz, 2H), 7.57 (d, J = 7.6 Hz, 2H), 7.33-7.41 (m, 9H), 7.27-7.32 (m, 5H), 7.20 (d, J = 8.8 Hz, 2H), 7.16 (td, J = 8.0, 1.2 Hz, 2H), 7.06 (dd, J = 6.8, 2.0 Hz, 4H), 4.03 (t, J = 6.8 Hz, 4H), 1.80-1.87 (m, 4H), 1.49-1.52 (m, 4H), 1.36-1.39 (m, 8H), 0.92 (t, J = 7,2 Hz, 6H);

13

C NMR (100 MHz, CDCl3, δ): 158.32, 152.55,

141.59, 140.20, 140.05, 137.98, 130.05, 128.33, 127.71, 127.74, 126.70, 126.40, 125.68, 123.05, 122.76, 120.32, 120.17, 119.46, 115.47, 109.62, 109.47, 104.25, 68.34, 65.64, 31.59, 29.24, 33



25.74, 22.61, 14.05. P-Org. Under a nitrogen atmosphere, Fluorenone (0.032 g, 0.178 mmol) and CzPhOC6 (0.061 g, 0.178 mmol) were dissolved in CH2Cl2 (1 mL). Then, Eaton’s Reagent (P2O5, 7.5 wt % in MeSO3H) (0.05 mL) was added to the reaction mixture and stirred at 40 oC for 10 h. After cooling to room temperature, CH2Cl2 (10 mL) and 2M Na2CO3 (5 mL) was added to quench the reaction by vigorous stirring. The mixture was extracted with CH2Cl2 (3 × 10 mL) and the organic phase was dried over anhydrous MgSO4. Then the solvent was removed and the residue was redissolved in CH2Cl2 (5 mL) and filtered with a 0.45 µm PTFE syringe filter. The copolymer was precipitated three times in MeOH and washed with acetone in a Soxhlet apparatus for 12 h, then dried under vacuum. Off-white powder (89 mg, 81%) was obtained. 1H NMR (400 MHz, CDCl3, δ): 8.17 (d), 8.02 (s), 7.89-7.95 (m), 7.85 (d), 7.80 (d), 7.60 (d), 7.47-7.54 (m), 7.00-7.45 (m). 4.04-4.07 (m), 1.84-1.89 (m), 1.53-1.58 (m), 1.42 (s), 0.95 (s); GPC: Mw = 1.9 × 104 g mol–1, PDI = 1.3 (against polystyrene standards). P-B-1. Under a nitrogen atmosphere, Fluorenone (0.032 g, 0.1777 mmol), CzPhOC6 (0.0604 g, 0.1759 mmol) and M-IrB (1.93 mg, 0.0018 mmol) were dissolved in CH2Cl2 (1 mL). Then, Eaton’s Reagent (P2O5, 7.5 wt % in MeSO3H) (0.05 mL) was added to the reaction mixture and stirred at 40 oC for 10 h. After cooling to room temperature, CH2Cl2 (10 mL) and 2M Na2CO3 (5 mL) was added to quench the reaction by vigorous stirring. The mixture was extracted with CH2Cl2 (3 × 10 mL) and the organic phase was dried over anhydrous Na2SO4. Then the solvent was removed and the residue was redissolved in CH2Cl2 (5 mL) and filtered using a 0.45 µm PTFE syringe filter. The copolymer was precipitated three times in MeOH and washed with acetone in a Soxhlet apparatus for 12 h, and finally dried under vacuum. Off-white powder (89 mg, 80%) was obtained. 1H NMR (400 MHz, CDCl3, δ): 8.14 (d), 8.00 (s), 7.89-7.95 (m), 34


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7.76-7.84 (m), 7.57 (d), 7.47-7.51 (m), 7.00-7.45 (m). 4.04-4.07 (m), 1.84-1.88 (m), 1.53-1.58 (m), 1.40 (s), 0.95 (s); GPC: Mw = 1.8 × 104 g mol–1, PDI = 1.4 (against polystyrene standards). P-B-2. It was prepared from Fluorenone (0.032 g, 0.1777 mmol), CzPhOC6 (0.0598 g, 0.1742 mmol), M-IrB (3.75 mg, 0.0035 mmol) and Eaton’s Reagent (0.05 mL), following the same procedure as for P-B-1. The polymer was obtained as off-white powder (Yield: 79%). 1H NMR (400 MHz, CDCl3, δ): 8.17 (d), 8.03 (s), 7.91-7.97 (m), 7.85 (d), 7.02-7.81 (m), 7.60 (d), 7.47-7.55 (m), 6.97-7.45 (m), 4.02-4.07 (m), 1.83-1.88 (m), 1.51-1.53 (m), 1.38-1.40 (m), 0.95-0.97 (m); GPC: Mw = 1.9 × 104 g mol–1, PDI = 1.3 (against polystyrene standards). P-B-3. It was prepared from Fluorenone (0.032 g, 0.1777 mmol), CzPhOC6 (0.0591 g, 0.1722 mmol), M-IrB (5.90 mg, 0.0055 mmol) and Eaton’s Reagent (0.05 mL), following the same procedure as for P-B-1. The polymer was obtained as yellowish white powder (Yield: 81%). 1H NMR (400 MHz, CDCl3, δ): 8.17 (d), 8.03 (d), 7.91-7.98 (m), 7.85 (d), 7.80 (d), 7.60 (d), 7.47-7.54 (m), 7.07-7.45 (m), 4.04-4.07 (m), 1.84-1.88 (m), 1.51-1.55 (m), 1.38-1.40 (m), 0.94-0.97 (m); GPC: Mw = 1.7 × 104 g mol–1, PDI = 1.5 (against polystyrene standards). P-B-4. It was prepared from Fluorenone (0.032 g, 0.1777 mmol), CzPhOC6 (0.0584 g, 0.1702 mmol), M-IrB (8.04 mg, 0.0075 mmol) and Eaton’s Reagent (0.05 mL), following the same procedure as for P-B-1. The polymer was obtained as yellowish white powder (Yield: 81%). 1H NMR (400 MHz, CDCl3, δ): 8.16 (d), 8.02 (d), 7.96 (s), 7.91-7.95 (m), 7.85 (d), 7.79 (d), 7.70-7.75 (m), 7.58-7.60 (m), 7.47-7.55 (m), 7.07-7.45 (m), 4.02-4.07 (m), 1.84-1.87 (m), 1.51-1.54 (m), 1.38-1.40 (m), 0.94-0.97 (m); GPC: Mw = 1.6 × 104 g mol–1, PDI = 1.6 (against polystyrene standards). P-W-1. Under a nitrogen atmosphere, Fluorenone (0.064 g, 0.3554 mmol), CzPhOC6 (0.1151 g, 0.3355 mmol), M-IrB (20.16 mg, 0.01880 mmol), M-IrO (1.27 mg, 0.0011 mmol) 35



were dissolved in CH2Cl2 (2 mL). Then, Eaton’s Reagent (0.1 mL) was added to the reaction mixture and stirred at 40 oC for 10 h. After cooling to room temperature, CH2Cl2 (15 mL) and 2M Na2CO3 (10 mL) was added to quench the reaction by vigorous stirring. The mixture was extracted with CH2Cl2 (3 × 15 mL) and the organic phase was dried over anhydrous Na2SO4. Then the solvent was removed and the residue was redissolved in CH2Cl2 (8 mL) and filtered using a 0.45 µm PTFE syringe filter. The copolymer was precipitated three times in MeOH and washed with acetone in a Soxhlet apparatus for 12 h, and finally dried under vacuum. Yellowish white powder (160 mg, 80%) was obtained. 1H NMR (400 MHz, CDCl3, δ): 8.15-8.17 (m), 8.02 (d), 7.89-7.95 (m), 7.82-7.84 (d), 7.76-7.78 (m), 7.71-7.75 (m), 7.58-7.60 (d), 7.49-7.55 (m), 7.02-7.41 (m), 4.00-4.05 (m), 1.82-1.87 (m), 1.50-1.54 (m), 1.38-1.40 (m), 0.93-0.96 (m); GPC: Mw = 1.8 × 104 g mol–1, PDI = 1.5 (against polystyrene standards). P-W-2. It was prepared from Fluorenone (0.064 g, 0.3554 mmol), CzPhOC6 (0.1152 g, 0.3357 mmol), M-IrB (20.16 mg, 0.01880 mmol), M-IrO (1.04 mg, 0.0009 mmol) and Eaton’s Reagent (0.10 mL), following the same procedure as for P-W-1. The polymer was obtained as yellowish white powder (Yield: 80%). 1H NMR (400 MHz, CDCl3, δ): 8.15-8.17 (m), 8.02 (d), 7.91-7.97 (m), 7.82-7.84 (d), 7.71-7.78 (d), 7.45-7.58 (m), 6.94-7.43 (m), 4.01-4.05 (m), 1.82-1.87 (m), 1.50-1.54 (m), 1.38-1.40 (m), 0.94-0.97 (m); GPC: Mw = 1.6 × 104 g mol–1, PDI = 1.4 (against polystyrene standards). P-W-3. It was prepared from Fluorenone (0.064 g, 0.3554 mmol), CzPhOC6 (0.1153 g, 0.3360 mmol), M-IrB (20.16 mg, 0.01880 mmol), M-IrO (0.69 mg, 0.00060 mmol) and Eaton’s Reagent (0.10 mL), following the same procedure as for P-W-1. The polymer was obtained as yellowish white powder (Yield: 82%). 1H NMR (400 MHz, CDCl3, δ): 8.15-8.17 (m), 8.01-8.03 (d), 7.91-7.97 (m), 7.84-7.86 (d), 7.78-7.80 (d), 7.72-7.73 (m), 7.58-7.60 (d), 36


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7.49-7.54 (m), 6.94-7.43 (m), 4.01-4.07 (m), 1.82-1.87 (m), 1.50-1.54 (m), 1.38-1.40 (m), 0.93-0.97 (m); GPC: Mw = 1.7 × 104 g mol–1, PDI = 1.6 (against polystyrene standards). OLED Fabrication and Measurements. The ITO glass substrates were pre-cleaned by ethanol, acetone and deionized water under an ultrasonic bath, then disposed to UV-ozone for half hour. The 40 nm-thick PEDOT:PSS layer was spin-coated on the ITO surface. After heating at 120 °C for half hour in the air, the EML (40 nm) was constructed by spin-coating a solution of each phosphorescent polymer in chlorobenzene. After dried in vacuum at 50 °C for 15 min, the obtained ITO chip was transferred to the deposition instrument for fabricating other layers of TPBi (40 nm), LiF (1 nm) and Al cathode (100 nm) under pressure less than 10–6 Torr. PR650 spectra colorimeter was used to measure the EL spectra and CIE coordinates of the OLEDs. Keithley 2400/2000 source meter was used to obtain the J–V−L characters of the OLEDs. All of these characterizations were conducted under ambient conditions.

ASSOCIATED CONTENT Supporting Information Synthesis of intermediate compounds, Absorption spectra of M-IrB and M-IrO, PL spectra of P-Org and M-IrB and some EL data. This material is available free of charge via the Internet at http://pubs.acs.org. Author Contributions B.A.L. prepared all the polymers and characterized the basic photophysical properties. Z.Z.T., Z.F. and D.Y.J. prepared some intermediate compounds. W.P.D. and X.L.Y. measured the CV curves. F.F.D. and Z.X.W. designed the structure of the OLEDs and F.F.D. fabricated all the devices. G.J.Z. designed the polymers supervised the overall project. G.J.Z. also contributed to 37



Page 38 of 47

analysis and writing of the whole paper.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. (G.J.Z.) *E-mail: [email protected]. (Z.X.W.) Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 21572716,

20902072),

the

China

Postdoctoral

Science

Foundation

(Grant

No.

20130201110034), the Fundamental Research Funds for the Central Universities (cxtd2015003) and the Key Creative Scientific Research Team in Yulin City of Shaanxi Province.

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