Synthesis and polarized photoluminescence of novel phosphorescent cyclometalated platinum dimer

Article abstract of DOI:10.1016/j.cclet.2011.01.032

A novel phosphorescent cyclometalated platinum dimer with bis-[2-(p-dodecyloxyphenyl) pyridyl]-hexane-1,6-diol as ligand and 1,3-(1-n-hexyl,3-n-heptadecyl) diketone as ancillary ligand was synthesized. The chemical structure and liquid crystal property of

Full text of DOI:10.1016/j.cclet.2011.01.032

Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1005–1008
www.elsevier.com/locate/cclet
Synthesis and polarized photoluminescence of novel
phosphorescent cyclometalated platinum dimer
b
a
Shi Ping Jiang a, Kai Jun Luo a, , Ying Han Wang , Xin Wang ,
*
Ying Jiang b, Yan Yan Wei a
a Institute of Chemistry and Materials, Sichuan Normal University, Chengdu 610081, China
b State Key Laboratory of Polymer Materials Engineering of China, College of Polymer Science and Engineering,
Sichuan University, Chengdu 610065, China
Received 27 October 2010
Available online 18 May 2011
Abstract
A novel phosphorescent cyclometalated platinum dimer with bis-[2-( p-dodecyloxyphenyl) pyridyl]-hexane-1,6-diol as ligand
and 1,3-(1-n-hexyl,3-n-heptadecyl) diketone as ancillary ligand was synthesized. The chemical structure and liquid crystal property
of the dimer were characterized by 1H NMR, ESI-MS, polarizing optical microscopy (POM) and differential scanning calorimetry
(DSC). The aligned film of title compound on the rubbed polyimide film is intensely emissive at room temperature with emission
maximum at 516 nm. The luminescence dichroic ratio (Ik/I ) at 516 nm is 3.1.
?
# 2011 Kai Jun Luo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Phosphorescent cyclometalated platinum dimer; Liquid crystal; Polarized photoluminescence; Synthesis
Recently, polarized organic luminescent materials and polarized organic light-emitting diodes (OLEDs) have
attracted much interest because of their possible application in industry of information, for example, they can be used
as back-lights for conventional liquid crystal displays [1–3]. In techniques of oriented thin films for polarized
photoluminescence (PL) and electroluminescence (EL), liquid crystalline luminescent materials are appropriate
candidates for their unique self-organizing nature and fluidity, which can be aligned on suitable alignment layers.
Generally, polarized light emission have been accomplished by annealing liquid crystalline polymeric luminescent
films, such as substituted poly( p-phenylenevinylene) (PPV), polyfluorene (PF) and their oligomers, on alignment
layers [4–12] or by aligning low molecular weight liquid crystal compounds with either benzothiazole or oxadiazole
units as chromophores [3,12–14]. Up to now, most liquid crystalline luminescent materials are fluorescent. In this
paper, a novel liquid crystalline phosphorescent cyclometalated platinum dimer, with bis-[2-( p-dodecyloxyphenyl)-
pyridyl]-hexane-1,6-diol as ligand and 1,3-(1-n-hexyl, 3-n-pentadecyl) diketone as ancillary ligand, was synthesized
and its polarized photoluminescence properties were investigated.
The synthetic route of title compound is shown in Scheme 1. The title compound was characterized by 1H NMR and
ESI-MS. 1H NMR (400 MHz, CDCl3): d 8.656 (d, 2H, J = 5.2 Hz), 8.161 (d, 2H, J = 8.4 Hz), 7.220 (d, 2H, J = 4 Hz),
* Corresponding author.
E-mail address: luo-k-j007@163.com (K.J. Luo).
1001-8417/$ – see front matter # 2011 Kai Jun Luo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.01.032

[()TD$FIG]
1006
S.P. Jiang et al. / Chinese Chemical Letters 22 (2011) 1005–1008
a
b
OH
I
OH
I
OC H
O
I
6
12
N
N
N
N
e
d
c
Br
OH
Br
N
O(CH ) CH
2 11
(HO) B
O(CH ) CH
2 11 3
3
2
f
H C(H C)
OC H
6 12
O
O(CH ) CH
3
2
16
2 11
3
N
H C(H C)
O
OC H O
6 12
O(CH ) CH
3
2
11
2 11
3
N
N
Pt
Pt
Pt
Cl
Cl
Cl
Cl
N
Pt
h
N
H C(H C)
O
OC H O
6 12
O(CH ) CH
3
2
11
2 11
3
CO(CH ) CH
3
g
2 16
CH (CH ) COOCH CH
3
2 16
2
3
CH
2
CO(CH ) CH
2 5
3
H C(H C)
O
OC H O
6 12
O(CH ) CH
3
2
11
2 11
3
N
N
Pt
Pt
O
O
O
O
H C(H C)
(CH ) CH
H C(H C)
(CH ) CH
2 16 3
3
2
16
2 5
3
3
2
5
Scheme 1. Synthetic route to the title compound. reagents and conditions: (a) water solution of potassium hydroxide (20%), iodine, potassium
iodide, room temperature, 8 h; (b) K2CO3, DMF, 1,6-dibromohexane, 110 8C, 4 h; (c) K2CO3, DMF, dodecyl bromide, 110 8C, 4 h; (d) argon,
tributy-borate, magnesium, THF, iodine, 40 8C, 4 h; (e) Pd(PPh3)4, tetrabutylammonium bromide, K2CO3, toluene, ethanol, water, 80 8C, 10 h; (f)
K2PtCl4, 3:1 mixture of 2-ethoxyethanol and water, 80 8C [15], 17 h; (g) sodium hydride, dimethylsulfoxide, 2-octanone, ethyl stearate, reflux, 6 h;
(h) 2-ethoxyethanol, cesium carbonate, 100 8C, 3 h.
7.190 (d, 2H, J = 1.2 Hz), 6.929 (dd, 2H, J1 = 5.6 Hz, J2 = 8.4 Hz), 6.627 (dd, 2H, J1 = 2.8 Hz, J2 = 8 Hz), 5.436 (s,
2H), 4.114 (t, 4H, J = 6.4 Hz), 4.059 (t, 4H, J = 6.8 Hz), 2.243 (dd, 8H, J1 = 7.2 Hz, J2 = 13.2 Hz), 1.996–2.014 (m,
4H), 1.680–1.839 (m, 16H), 1.425–1.561 (m, 8H), 1.282–1.325 (m, 96H), 0.887 (t, 18H, J = 2.4 Hz). MS (ESI):
2047.35[M+23]+.
The mesogenic behaviour of title compound was investigated by differential scanning calorimetry (DSC) and hot
stage polarizing optical microscopy (POM). The enantiotropic liquid crystal (LC) phase is assigned based on DCS
(Fig. 1) and polarized optical picture (Fig. 2). The title compound shows phase transition at 42 8C for crystalline-to-LC
and at 76 8C for LC-to-isotropic at the heating scan and at 65 8C for isotropic-to-LC and at 29 8C for LC-to-crystalline
at the cooling scan. The fanlike texture of title compound under polarized light indicates that title compound shows
smectic phase.
The aligned films of title compound on rubbed polyimide film were obtained by drop-casting CH2Cl2 solution of
the title compound (10ꢀ5 mol/L) onto glass substrate whose surface was coated with mechanically rubber polyimide
film and the films were dried and annealed at 65 8C for 2 h, and then quenched to room temperature. The luminescence
dichroic ratio (Ik/I ) is defined as the luminescence intensity parallel over that perpendicular to rubbed polyimide film.
?

[()TD$FIG]
S.P. Jiang et al. / Chinese Chemical Letters 22 (2011) 1005–1008
1007
Fig. 1. DSC thermogram of title compound (10 8C/min of heating and cooling rate).
[()TD$FIG]
Fig. 2. Polarized optical texture of title compound at 55 8C (obtained on cooling).
The luminescence dichroic ratio at room temperature was recorded on a Perkin Elmer LS55 fluorometer with the aid of
a polarizer. Fig. 3 shows polarized photoluminescence spectra of an aligned film of title compound. It is found that the
photoluminescence polarized parallel to the rubbed polyimide direction is much higher than that polarized
perpendicular to the rubbed polyimide direction. The luminescence dichroic ratio (Ik/I ) is 3.1 at 516 nm when
?
excitation wavelength is 390 nm. It is anticipated that title compound can be used as potential candidate for polarized
[()TD$FIG]
Fig. 3. Polarized photoluminescence spectra of title compound aligned on rubbed polyimide at RT (lex = 390 nm).

1008
S.P. Jiang et al. / Chinese Chemical Letters 22 (2011) 1005–1008
OLEDs because of its intensive phosphorescence and liquid crystal characteristics. The further research to improve the
degree of polarization of aligned film and the polarized OLED fabricated with title compound is in progress.
Acknowledgments
The work was supported by the National Natural Science Foundation of China (Nos. 20472060 and 21072141) and
Basic Research Fund of Education Bureau of Sichuan Province, China (No. 08ZA040).
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