Synthesis and characterization of deep blue emitters from starburst carbazole/fluorene compounds

Available online at www.sciencedirect.com

Tetrahedron 64 (2008) 2658e2668

www.elsevier.com/locate/tet

Synthesis and characterization of deep blue emitters

from starburst carbazole/ﬂuorene compounds

b

b,

Zujin Zhao ^a, Xinjun Xu ^b, Xiaopeng Chen ^a, Xiaoming Wang ^a, Ping Lu ^a,, Gui Yu , Yunqi Liu

*

^aDepartment of Chemistry, Zhejiang University, Hangzhou 310027, PR China

^bLaboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China

Received 21 September 2007; received in revised form 18 December 2007; accepted 21 December 2007

Available online 8 January 2008

Abstract

A series of well-deﬁned, highly ﬂuorescent starburst compounds with a carbazole core and oligo(2,7-ﬂuorene ethynylene) arms have been

synthesized by Sonogashira coupling reaction and fully characterized. These conjugated compounds exhibit good solubility, high thermal sta-

bility, and excellent ﬂuorescence quantum yields (up to 0.99). The incorporation of carbazole core interrupted the main-chain conjugation and

resulted in blue-shifted absorption and emission. Moreover, deep blue light has been approached from organic light-emitting diodes (OLEDs)

adopting these compounds as emitting layer.

Keywords: Blue emitter; Starburst molecules; Photoluminescence; Electroluminescence

1. Introduction

satisfactory due to their large energy gaps and low electron afﬁn-

ities leading to inefﬁcient electron injection into the blue

emitters.

Since the development of ﬁrst efﬁcient OLEDs by Tang and

VanSlyke,¹signiﬁcant attention has been paid on the produc-

tion of full-color ﬂat panel displays.^2,3Full-color displays

based on OLEDs exhibit many attractive features, such as

wide viewing angles, bright self-emission, facile color tunabil-

ity, and compatibility with ﬂexible substrates and now exist in

a range of commercial applications and compete with conven-

tional liquid-crystal displays (LCDs).^4e7To realize full-color

OLED displays, highly efﬁcient red-, green-, and blue-emit-

ting materials and devices are required. However, only red

and green materials and devices with sufﬁcient efﬁciencies

and lifetimes of commercial value have been described,^8e11

while high-efﬁcient, pure blue light still remains a challenge.

Consequently, a great number of blue-emitting materials,

such as anthracene derivatives,^12e15oligoquinoline,¹⁶tetra-

phenylsilane,^17,18and diarylﬂuorene derivatives^19,20have been

developed. However, most of these materials are still not

Monodisperse oligoﬂuorenes, ﬁrst reported by Klaerner and

Miller,²¹have recently attracted much attention because of

their excellent chemical, thermal, photochemical stabilities

as well as the possibility of structure tuning to adjust the

electronic and morphological properties of desired compounds

via the substitution on the C-9 position of ﬂuorene.^22,23Not

only does this class of materials have great potential applica-

tions for optoelectronic materials, such as blue emitters of

OLEDs,^24,25but also it would be very helpful to study the

properties of a series of pure compounds and to have a better

understanding of the structureeproperty relationships of their

corresponding polymers. On the other hand, carbazole units

hold hole-transport ability and incorporation of them could

improve the hole-transport properties of materials as well as

suppress the aggregation and/or excimers formation of mole-

cules.^26e29In this report, carbazole units were successfully

introduced into ﬂuorene compounds through 3-, 6-, and/or

9-positions of carbazole. Thus, linear and starburst structures

of molecules were obtained (Scheme 1). These synthesized

compounds emitted deep blue light with high quantum yields

* Corresponding authors. Tel./fax: þ86 571 879 52543.

E-mail address: pinglu@zju.edu.cn (P. Lu).

doi:10.1016/j.tet.2007.12.059

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

2659

N

Cz2F

C₇H₁₅

N

Cz2F3

C₇H₁₅

N

Cz2F5

C₇H₁₅

N

CzF6

Cz3F4

C₇H₁₅

N

C₇H₁₅

N

C₇H₁₅

N

CzF9

Cz4F6

C₇H₁₅

N

Scheme 1. Chemical structures of carbazole/ﬂuorene compounds.

and their applications in blue OLEDs were investigated

accordingly.

diethynyl-9-(4-ethynylphenyl)-9H-carbazole (12), which served

as a core of starburst molecules, was prepared by coupling 10

with 3-methyl-1-butyn-3-ol, and subsequently by deprotec-

tion. Fluorene derivatives 13 and 18³³were used to construct

the main chain of these conjugated molecules. Pd/Cu-cata-

lyzed coupling of 4 with an excess amount of 13 yielded

intermediate 14, which could be coupled with 3-methyl-1-bu-

tyn-3-ol in the presence of Pd/Cu catalyst and subsequently

base-promoted deprotection to provide compound 16. Recou-

pling of 16 with an excess amount of 13 afforded 17, which

served as arms of starburst compounds. Similar procedures

were performed to obtain 19.³³Coupling of 2,7-diethynyl-

9,9-diheptyl-9H-ﬂuorene (18) with 2 equiv of 2, 14, and 17

offered linear compounds Cz2F, Cz2F3, and Cz2F5 in

moderate yields of 86, 78, and 72% after separation, respec-

tively. Furthermore, treatment of 3,6-diethynyl-9-p-tolyl-9H-

2. Results and discussion

2.1. Synthesis

Structures of these well-deﬁned, carbazole end-capped and/

or centered ﬂuorene compounds are illustrated in Scheme 1. A

Pd/Cu-catalyzed Sonogashira coupling reaction was used as

a key reaction to construct these triple-bond-linked com-

pounds. Scheme 2 illustrates the synthetic routes to intermedi-

ates and ﬁnal compounds. Our synthetic strategy started from

commercially available compounds carbazole and ﬂuorene.

The cabazole derivatives 1e8^30,31and 9 and 10³²were synthe-

sized according to the reference methods. Compound 3,6-

2660

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

I

OH

N

I

N

R

3 R =

4 R =

I

N

13

d

c

b

a

C₇H₁₅C₇H₁₅

H

C₇H₁₅C₇H₁₅

N

H

i

14

2

1

4

I

R

OH

N

7 ^R=

8 R =

N

c

d

f

c

OH

N

15 R=

16 R =

e

R

N

d

H

6

H

N

H

C₇H₁₅C₇H₁₅

5

I

R

OH

g

f

h

11 R =

12 R =

I

N

d

N

13

C₇H₁₅C₇H₁₅

I

N

H

9

10

i

C₇H₁₅

17

C₇H₁₅

Br

R

i

N

I

N

I

Cz2F3

+

Cz2F

C₇H₁₅C₇H₁₅

C₇H₁₅

C₇H₁₅C₇H₁₅

C₇H₁₅

2

18

14

18

C₇H₁₅C₇H₁₅

Cz2F5

N

8

N

CzF6

8

i

Cz3F4

N

I

i

I

N

C₇H₁₅

C₇H₁₅C₇H₁₅

C₇H₁₅

12

N

17

19

CzF9

12

Cz4F6

Scheme 2. Conditions: (a) (CH₃)₃CCl, AlCl₃, CH₂Cl₂; (b) K₂CO₃, Cu, 18-crown-6, 1,4-diiodobenzene, DMF, N₂, 170 ^ꢀC; (c) 3-methyl-1-butyn-3-ol, Pd(PPh₃)₂Cl₂,

PPh₃, CuI, NEt₃, reﬂux; (d) KOH, 2-propanol, reﬂux; (e) K₂CO₃, Cu, 18-crown-6, 1-iodo-4-methylbenzene, DMF, N₂, 170 ^ꢀC; (f) KI, KIO₃, acetic acid, 80 ^ꢀC; (g)

K₂CO₃, Cu, 18-crown-6, 1-bromo-4-iodobenzene, DMF, N₂, 170 ^ꢀC; (h) 3-methyl-1-butyn-3-ol, Pd(Ph₃P)₄, Ph₃P, CuI, diisopropylamine, N₂, reﬂux; (i)

Pd(PPh₃)₂Cl₂, PPh₃, CuI, NEt₃, reﬂux.

carbazole (8) with 2 equiv of 19 and 17 provided Cz6F, and

Cz3F4 in 69 and 65% yields, respectively. Finally, CzF9 and

Cz4F6 were synthesized by the reactions of 3,6-diethynyl-9-

(4-ethynylphenyl)-9H-carbazole (12) with 3 equiv of 19 and

17, respectively, in the presence of Pd/Cu catalyst.

structures of compounds. Although the chains of all molecules

were composed of ﬂuorene units, the arrangement of ﬂuorene

units was quite interesting. Cz2F3 and Cz2F5, end-capped

with carbazole units, have rod-like structures and the ﬂuorene

units arranged alternatively in two different directions in back-

bones, which was in a good accordance with the arrangement

of ﬂuorene in its homopolymer. However, both CzF6 and

Cz3F4, with V-shaped structures, presented the arrangement

of ﬂuorene in one direction. This phenomenon could also

be observed in the propeller-like structures of CzF9 and

Cz4F6. From Figure 1, we inferred that it was much easier

for small and linear molecule Cz2F to form close molecular

packing than other compounds. The multifeasibility of the

free rotation along the molecular chain and the steric hin-

drance arising from the centered carbazole hampered the close

packing of the aromatic rings and thereafter hindered the ag-

gregation and/or excimer formation.

All compounds appeared to be yellow powder after dried in

vacuum. Structures of the target compounds were character-

ized by NMR, MALDI-TOF mass spectroscopy, and element

analysis. These compounds exhibited excellent solubility in

common organic solvents, such as CH₂Cl₂, CHCl₃, THF, tol-

uene, and even cyclohexane, which was ascribed to the exis-

tence of n-heptyl and tert-butyl substituents. Existence of

alkyl substituents not only beneﬁted the easier preparation

and puriﬁcation of compounds, but also helped the device fab-

rication via simple spin-coating. Further, these compounds

showed good thermal stabilities, and their decomposition tem-

peratures (T_d, 5% loss of initial weight) were above 400 ^ꢀC

examined by thermogravimetric analysis (TGA) in N₂at

a heating rate of 20 ^ꢀC min^ꢁ1. The melting and glass transition

temperatures were not clearly observed by differential scan-

ning calorimetry (DSC).

2.3. Photophysical properties

The photophysical properties of these compounds were ex-

amined by UVevis and ﬂuorescence spectroscopy in dichloro-

methane solutions and in thin neat ﬁlms as well. Figure 2

shows the normalized UVevis absorption spectra. In dilute di-

chloromethane solutions, all the compounds exhibited struc-

tureless absorption bands arising from the pep* transition

2.2. Visualization and simulation

Structures of the synthesized compounds were optimized

by PM3 method. Figure 1 illustrates the energy-minimized

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

2661

Figure 1. Energy-minimized structures of compounds calculated by PM3.

of the molecular chain. The maximum absorption peaks of lin-

ear compounds (Cz2F, Cz2F3, and Cz2F5) bathochromically

shifted with the increase of molecular length. The V-shaped

and the starburst compounds exhibited almost identical ab-

sorption bands with maximum absorption peaks at about

400 nm. The carbazole at the center of the molecules interrup-

ted the main-chain conjugation³⁴and resulted in relatively

short absorption wavelength with respect to that of Cz2F5.

In thin neat ﬁlms, the absorption spectra of these compounds

were quite similar to those in solutions except for slightly

red shifts (1e5 nm), which indicated that these compounds ex-

hibited very similar conformations in both solution and solid

states. The pep* energy gaps (E_g, Table 1) of these com-

pounds were calculated from the UVevis absorption thresh-

olds. The E_gs increased progressively with the decrease of

the chain length. The E_gs of the V-shaped and the starburst

compounds were 2.97 eV, which were higher than that of

Cz2F5. This was also attributed to the different conjugation

degree of molecules with or without centered carbazole core,

which could result in different energy levels.³⁵From Table

1, it was observed that the molar absorption coefﬁcient be-

came larger with the increase of the conjugation length or

the number of arms. Moreover, carbazole end-capped com-

pounds seemed to have relatively larger molar absorption

coefﬁcient compared with those of similar molecules without

carbazole cappers.

Figure 3 displays the emission spectra of compounds in

dilute CH₂Cl₂solutions and in thin neat ﬁlms as well, excited

at 380 nm. Cz2F3 and Cz2F5 showed narrow emission spectra

with a full width at half emission maximum (fwhm) of 14 nm

and emission peaks located at 417 and 421 nm, respectively.

Expectably, the shortest compound (Cz2F) exhibited a red-

shifted, broad emission peak at 422 nm with a fwhm of

65 nm, which was ascribed the excimers formation as

we assumed above. Much energy loss observed from the

largest Stokes shift (52 nm) was well evident. In view of

2662

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

(a)

(b)

1.2

Cz2F

1.0

0.8

0.6

0.4

0.2

0.0

CzF6

Cz2F3

Cz3F4

CzF9

1.0

Cz2F5

Cz4F6

0.8

0.6

0.4

0.2

0.0

300

350

400

Wavelength (nm)

450

500

300

350

400

Wavelength (nm)

450

500

(c)

(d)

1.0

0.8

0.6

0.4

0.2

0.0

1.0

0.8

0.6

0.4

0.2

0.0

Cz2F

CzF6

Cz3F4

CzF9

Cz2F3

Cz2F5

Cz4F6

300

350

400

Wavelength (nm)

450

500

300

350

400

Wavelength (nm)

450

500

Figure 2. Absorption spectra of compounds in dilute CH₂Cl₂solutions (a), (b), and in thin neat ﬁlms (c), (d).

carbazole-centered molecules, their emission spectra were

almost the same. Main emission peaks were located at about

415 nm with shoulder peaks at about 440 nm, which were

close to those of reported polyﬂuorenes (415 and 439 nm).³⁶

Similar to the observation in solutions, Cz2F exhibited broad,

red-shifted emission in thin neat ﬁlm due to the excimer

formation. Emission spectra in thin neat ﬁlms of other com-

pounds were resembled to those in solutions except for slight

red shifts (ꢂ6 nm).

increased as the chain lengths elongated. These ﬁndings

were much better than those of oligo(2,7-ﬂuorene ethynyl-

ene)s without carbazole participation (0.49e0.63).³³Remark-

ably, high quantum yields (0.97e0.99) were observed for

those starburst compounds with centered carbazole core,

which were higher than those of compounds with similar efﬁ-

cient conjugation length.³⁴For example, the quantum yield of

Cz4F6 was 0.99, while those of Cz2F and Cz2F3 were 0.74

and 0.89, respectively. Similar phenomena have been reported

by Yamaguchi et al.,⁴⁰which was ascribed to an extension of

the p conjugation between the arms of starburst molecules.

From higher PL quantum yields as well as larger molar ab-

sorption coefﬁcient of starburst compounds, we inferred that

the insertion of carbazole core into the molecular backbone

The synthesized compounds were highly ﬂuorescent in

solutions and in solid states. Quantum yields were measured

in degassed cyclohexanes using the standard of 9,10-diphenyl-

anthrecene (DPA, F¼0.95 in cyclohexane).^37e39Those of

linear ones were measured in the range of 0.74e0.96, which

Table 1

Photophysical properties of compounds

b

l_Em.(nm)

e

Compound

l_Abs.(nm)

F^c

fwhm^d

(nm)

Stokes

shift (nm)

E_g

(eV)

T_d

(nm)

(^ꢀC)

CH₂Cl₂(3ꢃ10⁵)^a

370 (0.97)

Film

CH₂Cl₂

Film

Cz2F

Cz2F3

Cz2F5

CzF6

CzF9

Cz3F4

Cz4F6

a

369

422

411, 447

423, 448

427, 452

419, 446

420, 444

421, 444

419, 443

0.74

0.89

0.96

0.97

0.99

0.98

0.99

65

14

16

20

16

52

16

12

13

14

15

14

3.02

2.93

2.90

2.97

413

420

419

415

411

421

416

385 (2.20), 401 (1.97)

391 (3.45), 409 (3.32)

381 (3.10), 402 (2.63)

382 (4.56), 401 (4.09)

382 (4.26), 400 (3.95)

382 (5.64), 400 (5.25)

383, 406

387, 410

381, 405

383, 404

382, 404

383, 402

417, 447

421, 446

415, 440

415, 439

415, 440

414, 439

Molar absorption coefﬁcient (3): M^ꢁ1cm^ꢁ1

.

b

c

d

e

Excited at 380 nm.

Measured in cyclohexane solutions using DPA as a standard.

Full width at half emission maximum in dilute CH₂Cl₂solutions (w10^ꢁ6M).

Determined from UVevis absorption spectra.

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

2663

(a)

(b)

1.0

0.8

0.6

0.4

0.2

0.0

1.0

Cz2F

CzF6

Cz2F3

Cz3F4

CzF9

0.8

Cz2F5

Cz4F6

0.6

0.4

0.2

0.0

350

400

450

Wavelength (nm)

500

550

600

350

400

450 500

Wavelength (nm)

550

600

(c)

(d)

1.0

0.8

0.6

0.4

0.2

0.0

CzF6

Cz2F

Cz3F4

CzF9

Cz2F3

Cz2F5

0.8

0.6

0.4

0.2

0.0

Cz4F6

350

400

450

500

550

Wavelength (nm)

600

650

700

350

400

450

500

550

Wavelength (nm)

600

650

700

Figure 3. PL spectra of compounds in dilute CH₂Cl₂solutions (a), (b), and in thin neat ﬁlms (c), (d).

might not interrupt the main-chain conjugation completely,

and a weak p conjugation still occurred between arms.

densityevoltageebrightness characteristic curves and Table 2

summarizes the performance of devices based on these com-

pounds. The EL spectra were similar to PL spectra in thin

neat ﬁlms, which indicated the same radiative decay process

of singlet excitons.^41,42In view of linear compounds, Cz2F

and Cz2F3 showed broad emission peaks with additional emis-

sions around 500 nm. This could be ascribed to the enhanced

excimer formation of these short chains that were prone to align

under electric ﬁelds.^43,44Cz2F5, with longer chain length, ex-

hibited EL emission peaks at 428 and 452 nm with a fwhm of

75 nm. No excimer emission was observed in this case. Further,

compounds with a carbazole core, except for Cz4F6 whose EL

emission was unstable, exhibited similar narrow emission with

fwhms in the range of 72e89 nm. The preliminary results dem-

onstrated that deep blue light could be approached from the

devices based on Cz2F5 and carbazole-centered compounds

2.4. Electroluminescence properties

To investigate the EL properties of these compounds, devices

with the conﬁgurations of indium tin oxides (ITO)/poly(3,4-eth-

ylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)

(30 nm)/compounds (50 nm)/1,3,5-tris(N-phenylbenzimid-

azol-2-yl)benzene (TPBI) (20 nm)/Al (100 nm), were fabricated.

PEDOT:PSS were used as a hole-injection layer, TPBI was

adopted as an electron-transporting and hole-blocking layer,

and the synthesized compounds functioned as light-emitting

layers. EL spectra as well as current densityevoltageebright-

ness characteristics were measured under ambient conditions.

Figures 4e6 illustrate the normalized EL spectra and current

(a)

(b)

1.0

CzF6

Cz2F

Cz2F3

Cz3F4

0.8

CzF9

Cz2F5

0.6

0.4

0.2

0.0

0.4

0.2

0.0

350 400 450 500 550 600 650 700 750

Wavelength (nm)

350 400 450 500 550 600 650 700 750

Wavelength (nm)

Figure 4. EL spectra of compounds in devices: ITO/PEDOT:PSS/compounds/TPBI/Al.

2664

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

(a)

(b)

CzF6

Cz2F

400

300

200

100

0

Cz2F3

Cz2F5

Cz3F4

300

CzF9

200

100

0

2

4

6

8

Voltage (V)

10 12 14 16

0

2

4

6

Voltage (V)

8

10

12

Figure 5. Brightnessevoltage diagrams for device: ITO/PEDOT:PSS/compounds/TPBI/Al.

(a)

(b)

CzF6

Cz2F

200

150

100

50

200

150

100

50

Cz3F4

CzF9

Cz2F3

Cz2F5

0

2

4

6

Voltage (V)

8

10

12

0

2

4

6

Voltage (V)

8

10 12 14 16

Figure 6. Current densityevoltage diagrams for devices: ITO/PEDOT:PSS/compounds/TPBI/Al.

Table 2

Summary of device performances

4. Experimental section

Compound EL (nm)

fwhm h_{max, ext}h_{max, L}Turn-on Brightness_max

(cd A^ꢁ1) voltage (cd m^ꢁ2, V)

(V)

4.1. General information

(nm) (%)

¹H and ¹³C NMR spectra were obtained on a Bruker

AVANCE DMX500 spectrometer operating in the FT mode.

Solutions in chloroform-d (5% w/v) were used to obtain

NMR spectra. TMS was used as an internal standard. Mass

spectroscopic (MS) measurements were carried using matrix-

assisted laser desorptioneionization time-of-ﬂight (MALDI-

TOF) technique. Fluorescence measurements were made with

a RF-5301PC spectroﬂuorometer (Shimadzu, Kyoto, Japan)

equipped with a xenon lamp. UVevis absorption spectra

were recorded on Shimadzu UV-2450 spectrophotometer.

NETZSCH STA 409 PG/PC was used to measure the thermal

performances of the compounds. The solvents were distilled

before used. Commercially available reagents were used with-

out further puriﬁcation.

Cz2F

468, 492 98 0.34

432, 468, 502 126 0.40

0.63

0.76

0.52

0.39

0.34

0.23

7.4

7.6

5.2

6.1

4.2

421, 13

155, 12.5

296, 9.0

230, 9.0

221, 9.0

222, 8.0

Cz2F3

Cz2F5

CzF6

428, 452

424, 448

420, 448

75 0.44

89 0.30

72 0.31

72 0.21

Cz3F4

CzF9

(Cz3F4 and CzF9). Introduction of carbazole units into molec-

ular backbone led to the color-stable, blue-shifted emission by

suppressing excimers formation.

3. Conclusions

In summary, we had successfully synthesized and fully

characterized a series of well-deﬁned, highly ﬂuorescent com-

pounds with a carbazole core and oligo(2,7-ﬂuorene ethynyl-

ene) arms. Addition of carbazole units signiﬁcantly

increased the ﬂuorescence quantum yields in comparison

with those of oligo(2,7-ﬂuorene ethynylene)s, especially for

carbazole-centered compounds. Moreover, participation of

carbazole interrupted the conjugation and resulted in blue-

shifted absorption and emission. Furthermore, deep blue light

had been approached from OLEDs based on these compounds

as emitters.

4.2. 3,6-Diethynyl-9-(4-ethynyl-phenyl)-9H-carbazole (12)

Compound 10 (2.87 g, 5 mmol), 3-methyl-1-butyn-3-ol

(1.68 g, 20 mmol), cuprous iodide (20 mg, 0.1 mmol), Pd(Ph₃P)₄

(11.5 mg, 0.01 mmol), triphenylphosphine (10.5 mg, 0.04 mmol),

and dry diisopropylamine (150 mL) were placed in a 250 mL

round bottle ﬂask equipped with a Teﬂon covered magnetic stir

bar. After the solution was purged with nitrogen for half an

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

2665

hour, it was reﬂuxed under nitrogen for 12 h. The reaction

mixture was ﬁltered and the ﬁltrate was evaporated under

reduced pressure. Compound 11 was obtained through col-

umn chromatography (silica gel, hexane/ethyl acetate as

eluent). Then 11, potassium hydroxide (2.0 g, 35 mmol),

and 2-propanol (150 mL) were placed in 250 mL round bot-

tle ﬂask equipped with a Teﬂon covered magnetic stir bar.

After the resulting mixture was reﬂuxed for 3 h under N₂,

it was cooled to room temperature. Solution was poured

into water and extracted by CH₂Cl₂. After washing by water

and drying by MgSO₄, the solvent was then removed, and the

residue was puriﬁed through column chromatography (silica

gel, hexane/dichloromethane as eluent). In this way, 1.2 g

0.02 mmol), and dry triethylamine (150 mL) were placed in

a 250 mL round bottle ﬂask equipped with a Teﬂon covered

magnetic stir bar. After the solution was purged with nitro-

gen for half an hour, it was reﬂuxed under nitrogen for

12 h. The reaction mixture was ﬁltered and the ﬁltrate was

evaporated under reduced pressure. The residue was puriﬁed

through column chromatography (silica gel, hexane/dichloro-

methane/ethyl acetate as eluent) to afford 15. Then 15, potas-

sium hydroxide (2.0 g, 35 mmol), and 2-propanol (150 mL)

were placed in 250 mL round bottle ﬂask equipped with

a Teﬂon covered magnetic stir bar. After the resulting mix-

ture was reﬂuxed for 3 h under N₂, it was cooled to room

temperature. Solution was poured into water and extracted

by CH₂Cl₂. After washing by water and drying by MgSO₄,

the solvent was then removed, and the residue was puriﬁed

through column chromatography (silica gel, hexane/dichloro-

1

(72 % total yield) of 12 was obtained. H NMR d CDCl₃:

3.10 (s, 2H), 3.20 (s, 1H), 7.32 (d, 2H, J¼8.5 Hz), 7.50

(d, 2H, J¼8.5 Hz), 7.55 (dd, 2H, J₁¼8.5 Hz, J₂¼1.5 Hz),

7.73 (d, 2H, J¼8.5 Hz), 8.26 (d, 2H, J¼1.0 Hz) ppm; ¹³C

NMR d CDCl₃: 76.17, 78.83, 82.83, 84.58, 110.18, 114.50,

122.20, 123.16, 124.99, 127.04, 130.80, 134.10, 137.30,

141.03 ppm; MS (EI) (m/z): 315 (M^þ). Anal. Calcd for

C₂₄H₁₃N: C, 91.40; H, 4.15; N, 4.44. Found: C, 91.41; H,

4.13; N, 4.38.

1

methane as eluent). Yield 62%. H NMR d CDCl₃: 0.61e

0.62 (m, 4H), 0.81(t, 6H, J¼7.5 Hz), 1.06 (br, 12H),

1.17e1.21 (m, 4H), 1.47 (s, 18H), 1.96e1.99 (m, 4H),

3.15 (s, 1H), 7.39 (d, 2H, J¼9.0 Hz), 7.47e7.50 (m, 4H),

7.54e7.58 (m, 4H), 7.65 (d, 1H, J¼7.5 Hz), 7.68 (d, 1H,

J¼8.0 Hz), 7.76 (d, 2H, J¼8.5 Hz), 8.14 (d, 2H,

J¼1.0 Hz) ppm; ¹³C NMR d CDCl₃: 14.29, 22.83, 23.99,

29.22, 30.23, 32.05, 32.25, 35.01, 40.55, 55.52, 77.57,

84.85, 89.48, 91.38, 109.47, 116.56, 120.19, 120.36,

121.02, 121.97, 122.20, 123.86, 123.98, 126.29, 126.67,

128.82, 131.07, 131.54, 133.23, 138.36, 139.17, 140.93,

141.40, 143.47, 151.32, 151.45 ppm; MS (MALDI-TOF)

(m/z): 763.9 (M^þ). Anal. Calcd for C₅₇H₆₅N: C, 89.59; H,

8.57; N, 1.83. Found: C, 89.60; H, 8.55; N, 1.80.

4.3. 3,6-Di-tert-butyl-9-[4-(9,9-diheptyl-7-iodo-9H-ﬂuoren-2-

ylethynyl)-phenyl]-9H-carbazole (14)

Compound 4 (379 mg, 1 mmol), 13 (1842 mg, 3 mmol), cu-

prous iodide (10 mg, 0.05 mmol), Pd(PPh₃)₂Cl₂(3.5 mg,

0.005 mmol), triphenylphosphine (5 mg, 0.02 mmol), and dry

triethylamine (150 mL) were placed in a 250 mL round bottle

ﬂask equipped with a Teﬂon covered magnetic stir bar. After

the solution was purged with nitrogen for half an hour, it

was reﬂuxed under nitrogen for 4 h. The reaction mixture

was ﬁltered and the ﬁltrate was evaporated under reduced pres-

sure. The residue was puriﬁed through column chromatogra-

phy (silica gel, hexane/dichloromethane as eluent). In this

way, 623 mg (72 % yield) of 14 was obtained. ¹H NMR

d CDCl₃: 0.62 (br, 4H), 0.80 (t, 6H, J¼7.5 Hz), 1.06e1.07

(m, 12H), 1.16e1.20 (m, 4H), 1.47 (s, 18H), 1.95e2.00

(m, 4H), 7.34 (d, 2H, J¼6.5 Hz), 7.39 (d, 2H, J¼8.0 Hz),

7.47e7.49 (m, 2H), 7.55e7.58 (m, 4H), 7.65e7.70 (m, 2H),

7.75e7.77 (m, 2H), 8.14 (d, 2H, J¼1.5 Hz) ppm; ¹³C NMR

d CDCl₃: 14.28, 22.82, 24.00, 29.21, 30.26, 32.04, 32.23,

34.99, 40.61, 55.40, 89.02, 91.57, 93.42, 109.46, 116.54,

119.92, 120.08, 120.27, 121.93, 123.16, 123.81, 123.96,

126.25, 126.65, 127.14, 127.81, 130.89, 132.37, 133.20,

136.26, 139.12, 141.87, 143.44, 151.30, 153.67 ppm; MS

(MALDI-TOF) (m/z): 739.7 (M^þꢁI). Anal. Calcd for

C₅₅H₆₄IN: C, 76.28; H, 7.45; I, 14.65; N, 1.62. Found: C,

76.25; H, 7.49; N, 1.58.

4.5. 3,6-Di-tert-butyl-9-{4-[7-(9,9-diheptyl-7-iodo-9H-

ﬂuoren-2-ylethynyl)-9,9-diheptyl-9H-ﬂuoren-2-ylethynyl]-

phenyl}-9H-carbazole (17)

The procedure is analogous to that described for 14. Yield

1

58%. H NMR d CDCl₃: 0.62 (br, 8H), 0.80e0.83 (m, 12H),

1.06e1.07 (m, 24H), 1.17e1.21 (m, 8H), 1.47 (s, 18H),

1.93e1.97 (m, 4H), 2.00e2.03 (m, 4H), 7.39e7.45 (m, 3H),

7.48 (dd, 2H, J₁¼8.5 Hz, J₂¼1.5 Hz), 7.53e7.59 (m, 8H),

7.65e7.71 (m, 5H), 7.77 (d, 2H, J¼8.5 Hz), 8.15 (d, 2H,

J¼1.5 Hz) ppm; ¹³C NMR d CDCl₃: 22.84, 23.94, 24.02,

29.20, 29.28, 30.19, 30.28, 32.05, 32.09, 32.25, 35.00,

40.54, 40.70, 55.54, 55.67, 89.47, 90.97, 91.03, 91.43,

93.37, 109.46, 116.55, 120.09, 120.27, 120.31, 121.92,

121.96, 122.02, 122.27, 122.43, 123.98, 126.13, 126.20,

126.52, 126.66, 131.01, 131.07, 132.34, 133.22, 136.25,

138.32, 139.14, 140.35, 140.61, 140.92, 141.13, 143.44,

150.49, 151.41, 153.64 ppm; MS (MALDI-TOF) (m/z):

1250.1 (M^þ). Anal. Calcd for C₈₄H₁₀₀IN: C, 80.67; H, 8.06;

I, 10.15; N, 1.12. Found: C, 80.70; H, 8.10; N, 1.10.

4.4. 3,6-Di-tert-butyl-9-[4-(7-ethynyl-9,9-diheptyl-9H-

ﬂuoren-2-ylethynyl)-phenyl]-9H-carbazole (16)

4.6. 2-((9,9-Diheptyl-7-iodo-9H-ﬂuoren-2-yl)ethynyl)-7-((9,9-

diheptyl-9H-ﬂuoren-2-yl)ethynyl)-9,9-diheptyl-9H-ﬂuorene (19)

Compound 14 (866 mg, 1 mmol), 3-methyl-1-butyn-3-ol

(168 mg, 2 mmol), cuprous iodide (10 mg, 0.05 mmol),

Pd(PPh₃)₂Cl₂(3.5 mg, 0.005 mmol), triphenylphosphine (5 mg,

The procedure is analogous to that described for 17. Yield

77%. ¹H NMR d CDCl₃: 0.61 (br, 12H), 0.78e0.83 (m, 18H),

2666

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

1.06 (br, 36H), 1.17e1.18 (m, 12H), 1.94e2.02 (m, 12H),

7.33e7.34 (m, 3H), 7.44 (d, 1H, J¼8.0 Hz), 7.52e7.58 (m,

8H), 7.66e7.71 (m, 7H) ppm; ¹³C NMR d CDCl₃: 14.29,

14.31, 22.83, 23.92, 23.98, 29.20, 29.24, 29.28, 30.18,

30.26, 32.04, 32.08, 40.54, 40.69, 40.75, 55.38, 55.50,

55.65, 90.60, 90.91, 91.05, 91.18, 93.38, 119.91, 120.08,

120.24, 121.63, 121.91, 122.12, 122.35, 122.41, 123.10,

126.10, 126.15, 127.11, 127.76, 130.81, 130.96, 132.30,

136.23, 140.33, 140.58, 140.65, 140.83, 141.00, 141.69,

150.45, 151.02, 151.24, 151.31, 151.34, 153.62 ppm; MS

(MALDI-TOF) (m/z): 1256.9 (M^þ). Anal. Calcd for

C₈₅H₁₀₉I: C, 81.17; H, 8.74; I, 10.09. Found: C, 81.19; H,

8.71.

¹³C NMR d CDCl₃: 14.29, 22.85, 24.04, 29.28, 30.29, 32.09,

32.26, 35.01, 40.71, 55.57, 89.48, 91.08, 91.12, 91.47,

109.47, 116.57, 120.27, 122.01, 122.04, 122.29, 122.35,

123.86, 123.99, 126.23, 126.27, 126.68, 131.03, 131.09,

133.23, 138.35, 139.17, 140.93, 140.99, 141.16, 143.47,

151.43 ppm; MS (MALDI-TOF) (m/z): 1886.3 (M^þ). Anal.

Calcd for C₁₄₁H₁₆₄N₂: C, 89.75; H, 8.76; N, 1.48. Found: C,

89.75; H, 8.75; N, 1.47.

4.7.3. 9,9⁰-(4,4⁰-(7,7⁰-(7,7⁰-(9,9-Diheptyl-9H-ﬂuorene-2,7-

diyl)bis(ethyne-2,1-diyl)bis(9,9-diheptyl-9H-ﬂuorene-7,2-

diyl))bis(ethyne-2,1-diyl)bis(9,9-diheptyl-9H-ﬂuorene-7,2-

diyl))bis(ethyne-2,1-diyl)bis(4,1-phenylene))bis(3,6-di-tert-

butyl-9H-carbazole) (Cz2F5)

1

4.7. General procedure for the synthesis of the compounds

Yield 72 %. H NMR d CDCl₃: 0.64 (br, 20H), 0.80e0.83

(Cz2F, Cz2F3, Cz2F5, CzF6, Cz3F4, CzF9, and Cz4F6)

(m, 30H), 1.08 (br, 60H), 1.18e1.20 (m, 20H), 1.47 (s, 36H),

2.02 (br, 20H), 7.40 (d, 4H, J¼8.5 Hz), 7.49 (dd, 4H,

J₁¼8.5 Hz, J₂¼2.0 Hz), 7.56e7.59 (m, 24H), 7.70e7.72 (m,

10H), 7.78 (d, 4H, J¼8.5 Hz), 8.15 (d, 4H, J¼1.5 Hz) ppm;

¹³C NMR d CDCl₃: 14.29, 22.84, 24.01, 29.29, 30.28, 32.08,

32.24, 35.00, 40.69, 40.76, 55.53, 75.90, 85.95, 89.45,

91.07, 91.43, 116.54, 120.27, 120.30, 121.95, 121.99,

122.23, 122.29, 123.81, 123.97, 126.17, 126.65, 131.01,

131.06, 133.22, 138.30, 139.12, 140.90, 140.96, 141.13,

143.43, 151.36, 151.40 ppm; MS (MALDI-TOF) (m/z):

2656.3 (M^þ). Anal. Calcd for C₁₉₉H₂₃₆N₂: C, 89.99; H,

8.96; N, 1.05. Found: C, 90.00; H, 9.00; N, 0.99.

These compounds were obtained following an essentially

similar procedure. An illustrative example is provided

for Cz2F: 3,6-di-tert-butyl-9-(4-iodophenyl)-9H-carbazole (2)

(962 mg, 2 mmol), 2,7-diethynyl-9,9-diheptyl-9H-ﬂuorene (18)

(410 mg,1 mmol),cuprousiodide(10 mg,0.05 mmol),dichloro-

bis(triphenylphosphine)palladium (II) (3.5 mg, 0.005 mmol),

triphenylphosphine (5 mg, 0.02 mmol), and dry triethylamine

(100 mL) were placed in a 150 mL round bottle ﬂask equipped

with a Teﬂon covered magnetic stir bar. After the solution was

purged with nitrogen for half an hour, it was reﬂuxed under nitro-

gen for 4 h. The reaction mixture was ﬁltered and the ﬁltrate was

evaporated under reduced pressure. The residue was puriﬁed

through column chromatography (silica gel, hexane/dichlorome-

thane as eluent) to get Cz2F (960 mg, 86% yield).

4.7.4. 3,6-Bis((7-((7-((9,9-diheptyl-9H-ﬂuoren-2-

yl)ethynyl)-9,9-diheptyl-9H-ﬂuoren-2-yl)ethynyl)-9,9-

diheptyl-9H-ﬂuoren-2-yl)ethynyl)-9-p-tolyl-9H-carbazole

(CzF6)

4.7.1. 9,9⁰-(4,4⁰-(9,9-Diheptyl-9H-ﬂuorene-2,7-diyl)

bis(ethyne-2,1-diyl)bis(4,1-phenylene))bis(3,6-di-tert-

butyl-9H-carbazole) (Cz2F)

Yield 69%. ¹H NMR d CDCl₃: 0.63e0.64 (m, 24H), 0.78e

0.83 (m, 36H), 1.05e1.08 (m, 72H), 1.15e1.20 (m, 24H),

1.98e2.03 (m, 24H), 2.51 (s, 3H), 7.33e7.37 (m, 8H), 7.45

(d, 4H, J¼2.5 Hz), 7.55e7.61 (m, 20H), 7.65 (dd, 2H,

J₁¼8.0 Hz, J₂¼1.5 Hz), 7.69e7.71 (m, 12H), 8.38 (d, 2H,

J¼1.0 Hz) ppm; ¹³C NMR d CDCl₃: 14.28, 21.54, 22.82,

22.85, 24.02, 29.24, 29.29, 30.28, 30.30, 32.06, 32.09,

40.69, 40.76, 55.41, 55.54, 89.39, 90.64, 91.02, 91.11,

91.13, 91.18, 110.44, 115.21, 119.91, 120.24, 121.64,

122.12, 122.26, 122.37, 122.68, 123.13, 123.19, 124.28,

126.13, 126.19, 127.13, 127.17, 127.76, 130.22, 130.84,

130.92, 130.98, 134.42, 138.38, 140.67, 140.70, 140.88,

140.99, 141.09, 141.36, 141.71, 151.05, 151.28, 151.38 ppm;

MS (MALDI-TOF) (m/z): 2564.5 (M^þ). Anal. Calcd for

1

Yield 86%. H NMR d CDCl₃: 0.67 (br, 4H), 0.82 (t, 6H,

J¼7.5 Hz), 1.10 (br, 12H), 1.18e1.22 (m, 4H), 1.47 (s,

36H), 2.01e2.05 (m, 4H), 7.40 (d, 4H, J¼8 Hz), 7.48

(dd, 4H, J₁¼8.5 Hz, J₂¼2 Hz), 7.57e7.59 (m, 8H), 7.71 (d,

2H, J¼7.5 Hz), 7.78 (d, 4H, J¼8.5 Hz), 8.14 (d, 4H,

J¼1.5 Hz) ppm; ¹³C NMR d CDCl₃: 14.30, 22.85, 24.05,

29.26, 30.28, 32.08, 32.26, 35.02, 40.65, 55.58, 89.50,

91.44, 109.48, 116.56, 120.33, 122.01, 122.12, 123.87,

123.99, 126.32, 126.70, 131.10, 133.25, 138.38, 139.19,

141.10, 143.48, 151.48 ppm; MS (MALDI-TOF) (m/z):

1117.7 (M^þ). Anal. Calcd for C₈₃H₉₂N₂: C, 89.20; H, 8.30;

N, 2.51. Found: C, 89.19; H, 8.41; N, 2.50.

C₁₉₃H₂₃₁N: C, 90.38; H, 9.08; N, 0.55. Found: C, 90.35; H,

9.08; N, 0.65.

4.7.2. 9,9⁰-(4,4⁰-(7,7⁰-(9,9-Diheptyl-9H-ﬂuorene-2,7-

diyl)bis(ethyne-2,1-diyl)bis(9,9-diheptyl-9H-ﬂuorene-7,2-

diyl))bis(ethyne-2,1-diyl)bis(4,1-phenylene))bis(3,6-di-tert-

butyl-9H-carbazole) (Cz2F3)

Yield 78%. ¹H NMR d CDCl₃: 0.65 (br, 12H), 0.82 (t, 18H,

J¼7.5 Hz), 1.08 (br, 36H), 1.18e1.21 (m, 12H), 1.47 (s, 36H),

2.02 (br, 12H), 7.40 (d, 4H, J¼9.0 Hz), 7.48 (dd, 4H,

J₁¼8.5 Hz, J₂¼2.0 Hz), 7.57e7.59 (m, 16H), 7.69e7.71 (m,

6H), 7.77 (d, 4H, J¼8.0 Hz), 8.15 (d, 4H, J¼1.0 Hz) ppm;

4.7.5. 9,9⁰-(4,4⁰-(7,7⁰-(7,7⁰-(9-p-Tolyl-9H-carbazole-3,6-

diyl)bis(ethyne-2,1-diyl)bis(9,9-diheptyl-9H-ﬂuorene-7,2-

diyl)bis(ethyne-2,1-diyl))bis(9,9-diheptyl-9H-ﬂuorene-7,2-

diyl)bis(ethyne-2,1-diyl))bis(4,1-phenylene))bis(3,6-di-tert-

butyl-9H-carbazole) (Cz3F4)

Yield 65%. ¹H NMR d CDCl₃: 0.65 (br, 16H), 0.82 (t, 24H,

J¼7.5 Hz), 1.08 (br, 48H), 1.18e1.22 (m, 16H), 1.47 (s, 36H),

2.02e2.04 (m, 16H), 2.52 (s, 3H), 7.36e7.41 (m, 6H), 7.45e

Z. Zhao et al. / Tetrahedron 64 (2008) 2658e2668

2667

7.50 (m, 8H), 7.56e7.60 (m, 20H), 7.65 (dd, 2H, J₁¼8.5 Hz,

J₂¼2.0 Hz), 7.71 (d, 8H, J¼7.5 Hz), 7.78 (d, 4H, J¼8.5 Hz),

8.14 (d, 4H, J¼1.5 Hz), 8.38 (s, 2H) ppm; ¹³C NMR

d CDCl₃: 14.30, 21.54, 22.85, 24.03, 29.28, 29.30, 30.29,

30.32, 32.10, 32.25, 35.01, 40.70, 40.77, 55.54, 55.55,

89.39, 89.45, 90.98, 91.14, 91.46, 109.46, 110.45, 115.20,

116.55, 120.22, 120.25, 120.28, 120.31, 121.99, 122.11,

122.37, 122.69, 123.19, 123.84, 123.98, 124.29, 126.11,

126.19, 126.22, 126.26, 126.67, 127.17, 130.23, 130.92,

131.02, 131.08, 133.23, 134.42, 138.32, 138.39, 139.15,

140.66, 140.89, 141.11, 141.16, 141.36, 143.45, 151.38,

151.42 ppm; MS (MALDI-TPF) (m/z): 2549.4 (M^þ). Anal.

Calcd for C₁₉₁H₂₁₃N₃: C, 89.94; H, 8.42; N, 1.65. Found: C,

89.98; H, 8.39; N, 1.45.

(MALDI-TOF) (m/z): 3683.2 (M^þ). Anal. Calcd for

₂₇₆H₃₁₀N₄: C, 90.00; H, 8.48; N, 1.52. Found: C, 89.97; H,

8.50; N, 1.72.

C

4.8. Fabrication and characterization of OLEDs

All the devices were fabricated on bare ITO substrates that

were cleaned by detergent, deionized water, acetone, and

ethanol. Poly(3,4-ethylenedioxythiophene):poly(4-styrenesul-

fonate) (PEDOT:PSS) was spin-coated on ITO glass, and

was baked under 100 ^ꢀC for 2 h. Compounds Cz2F, Cz2F3,

Cz2F5, CzF6, Cz3F4, CzF9, and Cz4F6 were spin-coated

onto PEDOTePSS layer from their toluene solutions. Films

of 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) and

Al cathodes were formed by vacuum deposition under a pres-

sure of 3ꢃ10^ꢁ4Pa. The deposition rate for TPBI and Al

4.7.6. 3,6-Bis((7-((7-((9,9-diheptyl-9H-ﬂuoren-2-

yl)ethynyl)-9,9-diheptyl-9H-ﬂuoren-2-yl)ethynyl)-9,9-

diheptyl-9H-ﬂuoren-2-yl)ethynyl)-9-(4-((7-((7-((9,9-

diheptyl-9H-ﬂuoren-2-yl)ethynyl)-9,9-diheptyl-9H-ﬂuoren-

2-yl)ethynyl)-9,9-diheptyl-9H-ﬂuoren-2-yl)ethynyl)phenyl)-

9H-carbazole (CzF9)

cathode layers was 1 and 5 A s^ꢁ1, respectively. The thickness

˚

of the thin ﬁlms was monitored by a quartz crystal oscillator

placed near the substrates and was calibrated ex situ by an

Ambios Technology XP-2 surface proﬁlometer. EL spectra

were recorded with a Photo Research PR-650 spectrophotom-

eter. Currentevoltage characteristics were measured with

a Hewlett-Packard 4140B semiconductor parameter analyzer.

A Newport 2835-C multifunction optical meter was used to

measure the luminescence output.

1

Yield 58%. H NMR d CDCl₃: 0.65 (br, 36H), 0.80e0.85

(m, 54H), 1.07e1.10 (m, 108H), 1.17e1.22 (m, 36H),

1.98e2.04 (m, 36H), 7.33e7.37 (m, 10H), 7.47 (d, 2H,

J¼8.0 Hz), 7.57e7.63 (m, 30H), 7.69e7.74 (m, 21H), 7.86

(d, 2H, J¼8.5 Hz), 8.42 (s, 2H) ppm; ¹³C NMR d CDCl₃:

14.27, 22.80, 22.84, 23.97, 29.22, 29.28, 30.26, 30.27,

32.04, 32.08, 40.67, 40.75, 55.37, 55.50, 90.60, 90.91,

90.98, 91.01, 91.06, 91.15, 110.38, 115.69, 119.90, 120.22,

121.62, 122.12, 122.18, 122.31, 122.52, 123.10, 126.10,

126.14, 126.19, 127.10, 127.75, 130.80, 130.90, 130.96,

133.45, 140.65, 140.72, 140.80, 140.85, 140.96, 141.01,

141.67, 151.00, 151.23, 151.34 ppm; MS (MALDI-TOF) (m/z):

3704.5 (M^þ). Anal. Calcd for C₂₇₉H₃₃₇N: C, 90.45; H, 9.17;

N, 0.38. Found: C, 90.44; H, 9.13; N, 0.42.

Acknowledgements

P.L. thanks the National Natural Science Foundation of

China (20674070) and the Natural Science Foundation of Zhe-

jiang Province (R404109). This work is partially supported by

the Major State Basic Research Development Program and the

Chinese Academy of Sciences.

Supplementary data

4.7.7. 9,9⁰-(4,4⁰-(7,7⁰-(7,7⁰-(9-(4-((7-((7-((4-(3,6-Di-tert-

butyl-9H-carbazol-9-yl)phenyl)ethynyl)-9,9-diheptyl-9H-

ﬂuoren-2-yl)ethynyl)-9,9-diheptyl-9H-ﬂuoren-2-

yl)ethynyl)phenyl)-9H-carbazole-3,6-diyl)bis(ethyne-2,1-

diyl)bis(9,9-diheptyl-9H-ﬂuorene-7,2-diyl)bis(ethyne-2,1-

diyl))bis(9,9-diheptyl-9H-ﬂuorene-7,2-diyl)bis(ethyne-2,1-

diyl))bis(4,1-phenylene))bis(3,6-di-tert-butyl-9H-carbazole)

(Cz4F6)

Supplementary data and representative spectra associated

with this article can be found in the online version, at

doi:10.1016/j.tet.2007.12.059.

References and notes

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Synthesis and characterization of deep blue emitters from starburst carbazole/fluorene compounds

DOI: 10.1016/j.tet.2007.12.059

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