Synthesis of efficient blue and red light emitting phenanthroline derivatives containing both hole and electron transporting properties

Article abstract of DOI:10.1016/j.tetlet.2004.06.087

Two phenanthroline derivatives containing a hole transporting triphenylamine and an electron transporting 1,3,4-oxadiazole unit have been prepared with high yield. UVa€"vis absorption and fluorescence measurement indicated they are high efficient light-em

Full text of DOI:10.1016/j.tetlet.2004.06.087

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 6361–6363
Synthesis of efficient blue and red light emitting
phenanthroline derivatives containing both hole
and electron transporting properties
a
Yuan Ji Bing,a,b Louis M. Leungb, and Gong Menglian
*
aState Key Laboratory of Optoelectronic Materials and Technologies, School of Chemistry and Chemical Engineering,
Sun Yat-sen University, Guangzhou 510275, China
bCentre for Advanced Luminescence Materials, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong SAR, PR China
Received 5 April 2004; revised 4 June 2004; accepted 8 June 2004
Abstract—Two phenanthroline derivatives containing a hole transporting triphenylamine and an electron transporting 1,3,4-oxad-
iazole unit have been prepared with high yield. UV–vis absorption and fluorescence measurement indicated they are high efficient
light-emitting materials. The compounds are 6-(5-(4-N,N0-diphenylaminophenyl)-1,3,4-oxadiazol-2-yl) quinoxalino[2,3-f] phen-
anthroline (9, kmax =635nm, 40% quantum yield), and 1-ethyl-2-(4-(5-(4-N,N0-diphenylaminophenyl)-1,3,4-oxadiazol-2-yl)phen-
yl)imidazo[4,5-f]phenanthroline (14, kmax =461nm, 78% quantum yield). Preliminary study on electroluminescence for the two
fluorescent dyes prepared from vacuum evaporation resulted in blue and red light emitting organic light emitting diodes (OLED).
ꢀ 2004 Elsevier Ltd. All rights reserved.
Classical chelates based on 2,20-bipyridyl and 1,10-phen-
anthroline have undergone an explosive development
are in parallel with the rapid development of coordina-
tion chemistry in past decade. The construction of
highly sophisticated molecular architecture incorporat-
ing various transition metals relies on the availability
of multifunctional ligands.1–4 In the course of develop-
ing such ligands, it is vital to have the disposal of facile
synthetic methods, which lead to the synthesis of novel
chelates bearing various functional groups with high
yield. Oxadiazoles, triphenylamine and their derivatives
are known electron and hole transporting materials and
are typically used for the construction of heterojunction
multi-layers OLED. The derivatives of phenanthroline,
which have excellent hole blocking and electron trans-
porting properties, are likely to have interesting value
in the construction of such molecular device too.5 Multi-
functional molecules containing all the three compo-
nents––triphenylamine, oxadiazole and phenanthroline
fused together had not been described in the literatures.
In this report, new synthetic procedures for the prepara-
tion of two such multifunctional 1,10-phenanthrolines
derivatives with different fluorescent characteristics with
good yield are described.
Our approach towards the preparation of multifunc-
tional phenanthroline derivatives relies on two types of
C@N bond formation. One can take advantage of the
easily access 1,10-phenanthroline-5,6-dione as the start-
ing material.5 1,10-Phenanthroline was treated with
H2SO4, HNO3 and KBr to afford 1,10-phenanthroline-
5,6-dione 6 with 80% yield. Reaction of 6 with equimo-
lar of 3,4-diaminobenzoic acid under HAC catalyst in
absolute ethanol afforded compound 7 with 90% yield.
Compounds 2–4 were synthesized according to methods
described in literature.6 Phenanthroline derivative 9 was
prepared from acid chloride compound 8 and 4 with
high yield (60%).7,8 A summary of the synthetic proce-
dures is shown in the following schematic diagram (see
Scheme 1).
In order to correlate the photoluminescent properties
with the effective conjugation length. Another multi-
functional phenanthroline compound with similar
structure was synthesized. The procedures are shown
in Scheme 2. Compounds 11, 12 were prepared by
Keywords: Phenanthroline derivatives; Fluorescence dyes; Hole and
electron transporting.
*
Corresponding author. Tel.: +852-3411-7073; fax: +852-3411-
7348; e-mail: s20974@hkbu.edu.hk
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.06.087

6362
Y. J. Bing et al. / Tetrahedron Letters 45 (2004) 6361–6363
DMF/
NH4Cl/
NaN3
POCl3,DMF
NH2OH . HCl
N
N
N
N
N
CN
N
N
N
H
O
3
4
2
1
O
O
O
O
3,4-Diamino
benzoic acid
N
N
HNO H SO
4
N
N
N
N
N
N
SOCl2
3,
2
Cl
OH
N
N
C H OH
KBr
2
5
N
N
5
6
8
7
N
N
+
4
N
N
N
N
N
O
N
9
Scheme 1. Synthetic routines for compound 9.
O
O
SOCl2
N
N
4
OH
+
Cl
OHC
OHC
CHO
N
O
10
11
12
H
N
N
N
N
N
N
C H Br
N
2
5
N
N
6
+
HAC
N
N
O
N
N
O
N
NaH,
DMF
NH AC
4
13
14
Scheme 2. Synthetic routines for compound 14.
procedures similar to 8, 9. Reaction of 6 and 12 in the
presence of pure acetic acid and ammonium acetate
afford compound 13 (80% yield).9,10 Compound 13
was then allowed to react with bromoethane under the
presence of NaH to obtain phenanthroline derivative
14 with over 50% yield.11 Both the final products 9
and 14 are soluble in CHCl3, THF and acetone.
C
B
D
A
1.0
0.8
0.6
0.4
0.2
0.0
1
All compounds were characterized by H NMR (JEOL
270 FT NMR) and MS (FAB).7,9–11 The absorption
and photoluminescent (PL) spectra of compounds 9
and 14 in THF are presented in Figure 1. The absorp-
tion spectrum of 9 extended into the visible region
shown typical CT band around 416nm and broad
pfip* transition band around 347nm is a result of ex-
tended conjugation of the phenanthroline moiety. Emis-
sion of compound 9 is red at 635nm (kex =416nm,
quantum yield=40%), whereas the absorption and emis-
sion maximum of 14 were 372, and 461nm (blue),
respectively, (kex =362nm, quantum yield=78%).12 The
significant differences in the emission characteristics of
9 and 14 are results of electron delocalization are being
allowed in between the six-member pyrazine ring and
phenyl-groups in 9 whereas the five-member imidazole
ring and phenyl-groups in 14 are connected through a
single bond with little p-conjugation. As the conjugation
200 300 400 500 600 700 800 900
Wavelength(nm)
Figure 1. UV–vis absorption and fluorescence spectra of compound 9
and 14 in THF (A, D represent UV–vis, PL spectra of 9, respectively;
B, C represent UV–vis, PL spectra of 14, respectively).
length of 9 is longer than that of 14, considerable batho-
chromic and hyperchromic shifts were observed.13
In conclusion, this report has described two synthetic
routes for the preparation of novel multifunctional
1,10-phenanthroline derivatives. The two compounds

Y. J. Bing et al. / Tetrahedron Letters 45 (2004) 6361–6363
6363
dry pyridine was added dropwise into the mixture, and
refluxed for three days. The crude product was concen-
trated under reduced pressure leaving a red residue. The
desired product was obtained by sol–gel column chroma-
tography using chloroform/hex (9:1) as the eluent.
6-(5-(4-N,N0-Diphenylaminophenyl)-1,3,4-oxadiazol-2-yl)
quinoxalino[2,3-f] phenanthroline (9): Yellow needle; mp
300ꢁC (DSC); 1H NMR (270MHz) d (ppm) (CDCl3) 9.64
(d, J=8.1Hz, 2H), 9.30 (s, 2H), 9.00 (s, 1H), 8.68 (d,
J=8.1Hz, 1H), 8.48 (d, J=8.1Hz, 1H), 8.02–8.07 (m, 2H),
7.80–7.85 (m, 2H), 7.30–7.39 (t, J=8.1Hz, 4H), 7.12–7.19
(m, 8H); MS (FAB): 594 (M++1). Anal. Calcd for
C38H23N7O C: 76.88%, H: 3.90%, N: 16.52%. Found C:
76.40%, H: 3.90%, N: 16.21%.
have different light-emitting characteristics but are both
functional charge transporting materials. We are cur-
rently exploring the photo and electroluminescent prop-
erties of these two compounds in OLEDs fabricated
from traditional vacuum deposition method. Further
studies for the two compounds to be used as metal coor-
dination ligand for multifunctional molecular materials
are under investigation.
Acknowledgements
This work is supported by a research grant from the re-
search grant council of the Hong Kong SAR Govern-
ment (grant number: HKBU 2037/02P) and from the
Scientific and technical project of Guangdong province
(B10502).
8. Krebs, F. C.; Spanggaard, H. J. Org. Chem. 2002, 7,
7185–7192.
9. 2-(4-N,N0-Diphenylaminephenyl)-5-(4-formalphenyl)-1,3,
1
4-oxadiazole (12). H NMR (270MHz) d (ppm) (CDCl3)
10.1 (s, 1H), 8.30 (d, J=8.1Hz, 2H), 8.04 (d, J=2.7Hz,
2H), 8.02–7.92 (m, 2H), 7.36–7.30 (m, 4H), 7.19–7.09 (m,
8H). MS (FAB): 418 (M++1).
10. 2-(4-(5-(4-N,N0-Diphenylaminophenyl)-1,3,4-oxadiazol-2-
yl)phenyl)imidazo[4,5-f] phenanthroline (13). 1H NMR
(270MHz) d (ppm) (DMSO-d6) 9.05 (dd, J=2.7, 5.4Hz,
2H), 8.99 (d, J=8.1Hz, 2H), 8.54 (d, J=8.1Hz, 2H), 8.32
(d, J=8.1Hz, 2H), 7.99 (d, J=8.1Hz, 2H), 7.89 (s, 2H),
7.40 (t, J=8.1Hz, 4H), 7.21–7.15 (m, 6H), 7.03 (d,
J=8.1Hz, 2H), 14.05 (N–H). MS (FAB): 608 (M++1).
11. 1-Ethyl-2-(4-(5-(4-N,N0-diphenylaminophenyl)-1,3,4-oxa-
diazol-2-yl)phenyl)imidazo[4,5-f] phenanthroline (14). 1H
NMR (270MHz) d (ppm) (CDCl3) 9.18 (dd, J=2.7,
5.4Hz, 2H), 9.09 (dd, J=2.7, 5.4Hz, 1H), 8.6 (d,
J=8.1Hz, 1H), 8.3 (d, J=5.4Hz, 2H), 8.01–7.93 (m,
4H), 7.75 (dd, J=5.4, 2.7Hz, 2H), 7.37–7.31 (m,4H), 7.20–
7.11 (m, 8H), 4.73 (dd, J=5.4, 2.7Hz, 2H), 1.67 (t,
J=8.1Hz, 5.4Hz, 3H). MS (FAB): 636 (M++1). Anal.
Calcd for C41H29N7OÆH2O, C: 75.33%, H: 4.78%, N:
15.00%. Found C: 74.87%, H: 4.96%, N: 14.78%.
12. Luminescence quantum yields were determined relative to
a reference solution of quinine sulfate in 1N sulfuric acid
(U=0.546) and corrected for the refractive index of the
solvent.
References and notes
1. Yasuda, T.; Yamaguchi, I.; Yamamoto, T. Adv. Mater.
2003, 15, 293–296.
2. Gong, X.; Ng, P. K.; Chan, W. K. Adv. Mater. 1998, 16,
1337–1340.
3. Meyer, M.; Kersting, B.; Powers, R. E.; Raymond, K. N.
Inorg. Chem. 1997, 36, 5179–5191.
4. Williams, A. F.; Piguet, C.; Bernardinelli, G. Angew.
Chem., Int. Ed. Engl. 1991, 30, 1490–1492.
5. Yamada, M.; Tanaka, Y.; Yoshimoto, Y.; Kuroda, S.;
Shimao, I. Bull. Chem. Soc. Jpn. 1992, 65, 1006–1011.
6. Tamoto, N.; Adachi, C.; Nagai, K. Chem. Mater. 1997, 9,
1077–1085.
7. General procedures for the synthesis of Compounds 8 and
9. To dipyrido(3,2-a,20,30-c)phenazine-8-carboxylic acid
(3.28g, 10mmol) was added thionyl chloride (60mL) and
the mixture was refluxed for 24h. The solution was
concentrated to 10mL under reduced pressure and then
benzene (40mL) was added. The benzene was removed
also under reduced pressure later. To the residue 200mL
dry pyridine was added and then stirred until dissolved.
The triphenylaminetetrazole (3.13g, 10mmol) in 100mL
13. Yang, J.-S.; Chiou, S.-Y.; Liau, K.-L. J. Am. Chem. Soc.
2002, 124, 2518–2527.