Syntheses and photoluminescence properties of rhenium(I) complexes based on dipyrido[3,2-a:2',3'-c]phenazine derivatives with carbazole moiety

Article abstract of DOI:10.1080/00958972.2013.773427

Four rhenium(I) complexes ReL¹-ReL4 based on dipyrido[3,2-a:2',3'-c]phenazine (L¹) and derivatives L ²-L4 ligands (L²: 10,13-dibromodipyrido[3,2-a:2',3'-c] phenazine, L³: 10-bromo-13-carbazolyl-dipyrido[3,2-a:2',3'-c] phenazine, L4: 10,13-dicarbazolyldipyrido[3,2-a:2',3'-c]phenazine) were synthesized and characterized. The Re(I) complexes ReL¹-ReL4 show photoluminescent emissions at 556, 582, 637 and 662 nm, respectively, assigned to dp (Re)→p/ (diimine) MLCT phosphorescence in CH₂CL ² solution. The carbazole containing complexes ReL³ and ReL4, as compared to ReL¹, exhibit higher luminescence. These observations imply that modification of diimine rhenium(I) carbonyl complexes with carbazole moiety would lead to efficient phosphorescent properties.

Full text of DOI:10.1080/00958972.2013.773427

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Syntheses and photoluminescence
properties of rhenium(I) complexes
based on dipyrido[3,2-a:2′,3′-
c]phenazine derivatives with carbazole
moiety
a b
a
a
Yong-Hui Zhou
, Zheng-Mei Wang , Min-Dong Chen , Sheng-Li
a
b
Guo & You-Xuan Zheng
a
Jiangsu Key Laboratory of Atmospheric Environment Monitoring
and Pollution Control , College of Environmental Science and
Engineering, Nanjing University of Information Science &
Technology , Nanjing , P.R. China
b
State Key Laboratory of Coordination Chemistry, Nanjing
National Laboratory of Microstructures , School of Chemistry and
Chemical Engineering, Nanjing University , Nanjing , P.R. China
Accepted author version posted online: 08 Feb 2013.Published
online: 20 Mar 2013.
To cite this article: Yong-Hui Zhou , Zheng-Mei Wang , Min-Dong Chen , Sheng-Li Guo & You-
Xuan Zheng (2013) Syntheses and photoluminescence properties of rhenium(I) complexes based
on dipyrido[3,2-a:2′,3′-c]phenazine derivatives with carbazole moiety, Journal of Coordination
Chemistry, 66:6, 958-965, DOI: 10.1080/00958972.2013.773427
To link to this article: http://dx.doi.org/10.1080/00958972.2013.773427
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Journal of Coordination Chemistry
Vol. 66, No. 6, 20 March 2013, 958–965
Syntheses and photoluminescence properties of rhenium(I)
complexes based on dipyrido[3,2-a:2′,3′-c]phenazine
derivatives with carbazole moiety
YONG-HUI ZHOU†‡, ZHENG-MEI WANG†, MIN-DONG CHEN†, SHENG-LI GUO†
and YOU-XUAN ZHENG*‡
†
Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control,
College of Environmental Science and Engineering, Nanjing University of Information
Science & Technology, Nanjing, P.R. China
‡
State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of
Microstructures, School of Chemistry and Chemical Engineering, Nanjing University,
Nanjing, P.R. China
(
Received 4 June 2012; in final form 28 November 2012)
Four rhenium(I) complexes ReL1–ReL4 based on dipyrido[3,2-a:2′,3′-c]phenazine (L1) and
derivatives L2-L4 ligands (L2: 10,13-dibromodipyrido[3,2-a:2′,3′-c]phenazine, L3: 10-bromo-13-
carbazolyl-dipyrido[3,2-a:2′,3′-c]phenazine, L4: 10,13-dicarbazolyldipyrido[3,2-a:2′,3′-c]phenazine)
were synthesized and characterized. The Re(I) complexes ReL1–ReL4 show photoluminescent
⁄
emissions at 556, 582, 637 and 662 nm, respectively, assigned to dp (Re)→p (diimine) MLCT
2 2
phosphorescence in CH Cl solution. The carbazole containing complexes ReL3 and ReL4, as com-
pared to ReL1, exhibit higher luminescence. These observations imply that modification of diimine
rhenium(I) carbonyl complexes with carbazole moiety would lead to efficient phosphorescent
properties.
Keywords: Rhenium(I) complex; Dipyrido[3,2-a:2′,3′-c]phenazine; Carbazole; Phosphorescence
emission
1. Introduction
Organic light emitting diodes (OLEDs) based on transition metal complexes [1–5]
have received considerable attention for high-emission quantum efficiency and rich
excited-state behavior. Rhenium complexes [6–11] often exhibit extraordinary luminescent
properties and play an important role in the photophysics and photochemistry of transition
metal complexes. In particular, the rhenium(I) tricarbonyl complexes fac-Re(CO) (L)X,
3
where L is a bidentate diimine ligand and X is a halogen, have been studied and applied
in various areas such as electroluminescent materials in OLED devices [12], solar energy
conversion [13] and photocatalytic CO reduction [14, 15].
2
However, performances of Re(I) complex-based OLEDs are far from practical
application in electroluminescence because of serious triplet–triplet annihilation (TTA) of
*
Corresponding author. Email: yxzheng@nju.edu.cn
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online Ó 2013 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2013.773427

Rhenium(I) complexes
959
the emitters, caused by saturation of the emissive sites, which leads to low efficiency at
high current density [16–18]. Many efforts have been focused on both the ligand structure
and rigidity of the complexes to tune the excited state properties. Basically, there are two
strategies to overcome the above mentioned shortcoming: (i) through the synthesis of
novel diimine ligands with different ligand-field (molecular design) [19–21] that would
modify the molecular orbital energy levels in the Re(I) complexes and (ii) by addition of
functional groups with electron-accepting or -donating properties into the diimine ligands
[22–26] in order to avoid the TTA by steric hindrance effect. Accordingly, we synthesized
and reported Re(I) complexes with carbazole and oxadiazole moieties showing enhanced
luminescence properties [10, 27].
With consideration of these reasons, we synthesized the dipyrido[3,2-a:2′,3′-c]phenazine
(
1
L1) and derivatives (L2: 10,13-dibromodipyrido[3,2-a:2′,3′-c]phenazine, L3: 10-bromo-
3-carbazolyl-dipyrido[3,2-a:2′,3′-c]phenazine, L4: 10,13-dicarbazolyl-dipyrido[3,2-a:2′,3′-
c]phenazine) and their corresponding Re(I) complexes ReL1–ReL4. The appended
carbazole moieties widen the absorption profile and act as light-harvesting units, improving
the hole-transporting ability and luminescence, preventing crystallization of complexes and
increasing the solubility in common organic solvents. All the complexes show good
phosphorescent emission.
2
2
. Experimental
.1. Materials and measurements
Rhenium pentacarbonyl chloride and 1,3-dimethyl-3,4,5,6-terahydro-2(1H)-pyrimidinone
DMPU) were bought from Alfa Aesar Co. (China). Carbazole, CuI, 18-Crown-6 and
K CO were purchased from Yuan Hang Reagent Co. (China). All were used as received.
(
2
3
The solvents except toluene were used without purification.
ꢀ1
IR spectra were taken on a Vector22 Bruker spectrophotometer (400–4000 cm ) with
1
KBr pellets. H NMR spectra were measured on a Bruker AM 500 spectrometer. Elemen-
tal analyzes for C, H, and N were performed on an Elementar Vario MICRO analyzer.
Absorption and emission spectra were measured on a UV-3100 spectrophotometer and a
Hitachi F4600 luminescence spectrophotometer, respectively. Photoluminescence lifetimes
were measured with an Edinburgh Instruments FLS920P fluorescence spectrometer. Lumi-
nescence quantum efficiencies were calculated by comparison of the emission intensities
(
integrated areas) of a standard sample (air-equilibrated and degassed acetonitrile solution
2
+
ꢀ
of [Ru(bpy) ] ·2Cl ) and the unknown sample according to the equation [28]:
3
ꢀ
ꢁꢀ
ꢁꢀ
ꢁ
2
I
unk
std
A
std
gunk
gstd
ꢀunk ¼ ꢀstd
I
A
unk
where, ꢀunk and ꢀstd are the luminescence quantum yields of the unknown sample and
2
+
ꢀ
air-equilibrated acetonitrile solution of [Ru(bpy) ] ·2Cl , respectively. I
and I are
std
3
unk
2
+
ꢀ
the integrated emission intensities of the unknown sample and [Ru(bpy) ] ·2Cl
3
solution, respectively. The A
and Astd are the absorbance of the unknown sample and
unk
2
+
ꢀ
[
Ru(bpy) ] ·2Cl acetonitrile solution at their excitation wavelengths (A < 0.1), respec-
3
tively. The gunk and gstd terms represent the refractive indices of the corresponding solvents
pure solvents were assumed). The ꢀ of air-equilibrated and degassed acetonitrile
(
std
2
+
ꢀ
solution of [Ru(bpy) ] ·2Cl are 0.018 and 0.094, respectively.
3

9
60
.2. Syntheses
Y.-H. Zhou et al.
2
The chemical structures of the materials used in this work and the synthetic routes are
depicted in scheme 1. 2,1,3-Benzothiadiazole (1), its derivatives (2–4), 1,10-phenanthro-
line-5,6-dione, L1–L4 and their corresponding Re(I) complexes were synthesized
according to the published literature (figures S1–S12) [29–31].
2
1
.2.1. Synthesis of 10-bromo-13-carbazolyl-dipyrido[3,2-a:2′,3′-c]phenazine (L3) and
0,13-dicarbazolyl-dipyrido[3,2-a:2′,3′-c]phenazine (L4). The solution of precursor 3
ꢀ
3
or 4 (0.56 mmol), NaBH4, (11.2 mmol) and CoCl ·6H O (5.6 ꢁ 10 mmol) in 30 mL of
2
2
ethanol was stirred with exclusion of light for 48 h at 70 °C. After cooling, 2.8 mmol 1,10-
phenanthroline-5,6-dione in 10 mL ethanol and 5 mL hartshorn were added and the solu-
tion was refluxed for 8 h. The solvent was removed under vacuum; the crude product was
purified by column chromatography on silica gel using ethyl acetate and petroleum ether
(
v/v = 1 : 3) as eluant to obtain L3 and L4.
L3: yield: 24%, M.p.: >300 °C. IR (KBr, cm ): 3010, 1641, 1450, 1081, 802, 738. H
NMR (500 MHz, CDCl , ppm) δ 9.622 (d, J = 9.0 Hz, 1H), 9.220 (d, J = 4.0 Hz, 1H),
ꢀ
1
1
3
9
.055 (d, J = 4.0 Hz, 1H), 8.492 (d, J = 9.0 Hz, 1H), 8.405 (d, J = 8.5 Hz, 1H), 8.235
(d, J = 8.5 Hz, 2H), 8.154 (d, J = 7.0 Hz, 1H), 8.103 (t, J = 7.5, 1H), 7.772–7.746 (m, 1H),
7
.362–7.333 (m, 2H), 7.307–7.280 (m, 2H). MS matrix-assisted laser desorption/ionization
N
Br
Br
N
N
N
S
NH2
NH2
N
N
N
+
Et N/CH Cl
Br /HBr
N
N
3
2
2
2
N
H
S
N
S
S
SOCl , reflux 5h
N
2
reflux 6h
CuI,18-Crown-6,
K CO , DMPU
2 3
1
Br
O
N
O
N
2
3
4
EtOH
NaBH
4
reflux, 5 h
CoCl .6H O
2 2
EtOH, rt, 20 h
NaBH , EtOH
4
reflux, 48 h
Br
NH
NH2
N
N
N
N
N
N
NH
2
NH 2
NH 2
N
Br
O
L1
O
N
NH 2
EtOH
reflux, 5 h
Br
N
O
N
O
N
Br
Br
EtOH
reflux, 5 h
N
N
N
N
N
N
N
N
N
L2
R2
R1
N
N
N
N
R2
R1
N
N
N
CO
N
Re(CO) Cl
N
N
N
N
5
CO
CO
Re
N
toluene, reflux, 3 h
Br
N
Cl
L3
L4
ReL1-ReL4
ReL1=Re(CO) ClL1, R =R =H;
ReL2=Re(CO) ClL2, R =R =Br;
3 1 2
3
1
2
ReL3=Re(CO) ClL3, R =Br, R =Carbazole;
ReL4=Re(CO) ClL4, R =R =Carbazole
3 1 2
3
1
2
Scheme 1. The syntheses for 1–4, L1–L4 and ReL1–ReL4.

Rhenium(I) complexes
961
+
time of flight (MALDI-TOF): m/z 526.455 [M] . Anal. Calcd for C H N Br (%): C,
3
0 16 5
6
8.45; H, 3.06; N, 13.31. Found: C, 67.93; H, 3.64; N, 13.72.
ꢀ
1
L4: yield: 26%, M.p.: >300 °C. IR (KBr, cm ): 3047, 1595, 1497, 1448, 1227, 1085,
1
7
2
47. H NMR (500 MHz, CDCl , ppm) δ 9.195 (d, J = 2.0 Hz, 2H), 8.554 (d, J = 4.0 Hz,
H), 8.451 (t, J = 1.0, 2H), 8.352–8.331 (m, 4H), 7.515–7.491 (m, 2H), 7.438–7.414
3
+
(m, 8H), 7.370–7.349 (m, 4H). MS (MALDI-TOF): m/z 613.434 [M + 1] . Anal. Calcd for
C H N (%): C, 82.33; H, 3.97; N, 13.72. Found: C, 82.17; H, 4.05; N, 13.61.
4
2 24 6
2
.2.2. General synthesis of ReL1–ReL4. Re(CO) Cl (0.035 g, 0.10 mmol) was refluxed
5
with equimolar quantities of L1–L4, respectively, in 30 mL toluene for 6 h under nitrogen.
After the mixture was cooled, the crude product was filtered and purified by column
chromatography on silica gel using ethyl acetate and petroleum ether (v/v = 1 : 2, together
with a small amount of triethylamine) as eluant to give the corresponding Re(I) complexes
ReL1–ReL4.
ꢀ
1
ReL1 (yield: 71%): IR (KBr, cm ): 2018, 1920, 1902, 1884, 1489, 1416, 1358, 1077,
1
8
8
22, 771, 727, 471. H NMR (500 MHz, CDCl , ppm) δ 9.897 (dd, 2H), 9.492 (dd, 2H),
3
+
.483 (m, 2H), 8.094 (m, 2H), 8.051 (m, 2H). MS (MALDI-TOF): m/z. 553.238 [M–Cl] .
Anal. Calcd. for C H N O ClRe (%): C, 42.90; H, 1.71; N, 9.53. Found: C, 43.08; H, 1.65;
2
1 10 4 3
N, 9.42.
ꢀ1
ReL2 (yield: 75%): IR (KBr, cm ): 2024, 1920, 1889, 1641, 1485, 1099, 824, 730,
1
4
77. H NMR (500 MHz, CDCl , ppm) δ 9.943 (dd, 2H), 9.537 (dd, 2H), 8.284 (s, 2H),
3
+
8
.106 (m, 2H). MS (MALDI-TOF): m/z. 711.086 [M–Cl] . Anal. Calcd for
C H N O ClRe (%): C, 33.82; H, 1.08; N, 7.51. Found: C, 33.67; H, 1.53; N, 7.42.
ReL3 (yield: 69%): IR (KBr, cm ): 2020, 1890, 1640, 1448, 1260, 1091, 800, 472. H
2
1 8 4 3
ꢀ1
1
NMR (500 MHz, CDCl , ppm) δ 9.910 (d, J = 6.5 Hz, 1H), 9.498 (d, J = 5.5 Hz, 1H),
3
9
.320 (d, J = 7.0 Hz, 1H), 9.645 (d, J = 9.5 Hz, 2H), 8.351 (d, J = 8.5 Hz, 1H), 8.304 (t,
J = 8.0 Hz, J = 5.0 Hz, 2H), 8.080–8.054 (m, 1H), 7.668–7.642 (m, 1H), 7.398–7.315 (m,
H), 7.710 (d, J = 7.5 Hz, 1H), 7.096 (d, J = 8.5 Hz, 1H). MS (MALDI-TOF): m/z.718.128
4
+
[M–Br–Cl] . Anal. Calcd for C H N O ClBrRe (%): C, 47.60; H, 1.94; N, 8.41. Found:
33 16 5 3
C, 74.32; H, 2.33; N, 8.66.
ꢀ1
ReL4 (yield: 67%): IR (KBr, cm ): 2020, 1889, 1624, 1496, 1447, 1093, 799, 750,
1
7
24, 464. H NMR (500 MHz, CDCl , ppm) δ 3.326 (dd, 2H), 8.675 (dd, 2H), 8.566
3
(
(
s, 2H), 8.354 (t, J = 5.0 Hz, 4H), 7.693–7.666 (m, 2H), 7.453–7.373 (m, 8H), 7.275
d, J = 8.0 Hz, 4H). MS (MALDI-TOF): m/z. 883.158 [M–Cl] . Anal. Calcd. for
+
C H N O ClRe (%): C, 54.93; H, 2.63; N, 9.15. Found: C, 54.82; H, 2.91; N, 9.02.
4
5 24 6 3
3
3
. Results and discussion
.1. Synthesis
Dipyrido[3,2-a:2′,3′-c]phenazine (L1) can be synthesized from reaction of o-phenylenedi-
amine and 1,10-phenanthroline-5,6-dione in good yield. To synthesize L2, it is necessary to
prepare 3,6-dibromo-o-phenylenediamine from 4,7-dibromobenzothiadiazole with NaBH4
as a reducing agent first. To prepare L3 and L4, CoCl ·6H O is used as the catalyst
2
2
together with the reducing agent NaBH to get the diamine intermediates 3-bromo-6-carbaz-
4
oly-o-phenylenediamine and 3,6-dicarbazoly-o-phenylenediamine. Because it is difficult to
purify the intermediate products, we used the “one pan” method to synthesize L3 and L4

9
62
Y.-H. Zhou et al.
where excess 1,10-phenanthroline-5,6-dione was added to the above mixture and the
solution was refluxed for 8 h. Probably due to high conjugation by carbazole decreasing the
reaction activity, yields for preparation of L3 and L4 are not high (around 25%).
3
.2. Optical property
UV–vis absorption spectra of L1–L4 and ReL1–ReL4 in CH Cl solutions with the same
2
2
ꢀ
4
ꢀ1
concentration (1 ꢁ10 mol L ) are shown in figure 1. Compared with L1, absorption of
L2 red shifts with similar shape. For L3 and L4, complicated peaks were observed due to
introduction of carbazole moieties. On comparison with the absorption spectra of L1, L2
and the results of our former studies [10, 27], peaks at 258, 290 and 335 nm belong to the
⁄
p–p transition of carbazole. Absorption spectra of the Re(I) complexes exhibit bathochro-
mic shift compared to the corresponding ligands at ca. 220–390 nm with extinction
4
ꢀ1
⁄
coefficients of 10 mol L cm , which can be assigned to spin-allowed intraligand (p→p )
transitions. Introduction of carbazole improves the absorption and molar extinction coeffi-
cient among these complexes. From previous studies on related rhenium(I) systems [6–27],
[
32, 33], at low energy bands (>390 nm) there should be metal to ligand charge-transfer
⁄
dp (Re)→p (diimine) (MLCT) absorptions, but in our complexes the MLCT absorptions
are very weak.
Figure 2 shows the photoluminescence spectra of the ligands and complexes in CH Cl
2
2
solutions at room temperature. For L1, the maximum is 502 nm which is bluish-green
color. When the two bromines were introduced, the emission of L2 red shifts to yellowish-
⁄
green (λmax = 560 nm). From the former report [24], the energy of the p orbital is lowered
by the electron-withdrawing moiety and heightened by introduction of an electron-donating
moiety. For L3 and L4, the emissions also red shift to 594 and 617 nm, respectively, due
to delocalization of p-electrons in the carbazole ring system through the electron-donating
carbazole.
⁄
Excited at the p→p absorption, ReL1–ReL4 show broad bands centered at ca. 556,
5
82, 637 and 662 nm (figure 2(b)) assigned to dp(Re)→p⁄ (diimine) MLCT phosphores-
cence [32], respectively. Heavy metal would provide efficient spin-orbit coupling facilitating
intersystem crossing and thereby enhance the orbital crossing in the singlet–triplet forbidden
transition [32]. Thus, strong phosphorescence can be observed. Compared with the emission
(a)
(b)
L1
L2
L3
L4
ReL1
ReL2
ReL3
ReL4
2
50
300
350
400
450
250
300
350
400
450
Wavelength (nm)
Wavelength (nm)
solution (1 ꢁ10ꢀ mol L
4
ꢀ1
)
Figure 1. UV–vis absorption spectra of L1–L4 (a) and ReL1–ReL4 (b) in CH
at room temperature.
2
Cl
2

Rhenium(I) complexes
963
(a)
(b)
L1
ReL1
ReL2
ReL3
ReL4
L2
L3
L4
4
00
500
600
700
800
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
solution (1 ꢁ10ꢀ mol L ) at room
4
ꢀ1
2 2
Figure 2. Emission spectra of L1–L4 (a) and ReL1–ReL4 (b) in CH Cl
temperature.
bands in ReL1, the maximum MLCT emission bands red shift in ReL2–ReL4, implying
that the ligand substituents affect the MLCT emission energies of the complexes. The
emissions of ReL3 and ReL4 show obvious red shift because of the high conjugation
caused by the carbazole.
Intensity of the MLCT emission and the quantum efficiency (ꢀ) of the corresponding
Re(I) complexes are also enhanced after introduction of carbazole, similar to that observed
in electronic absorption spectroscopy. Improvement of absorbance and luminescence inten-
sities of the samples by the presence of carbazole is due to the broad and strong absorption
bands of carbazole from 220 to 350 nm, in favor of energy absorption and energy transfer
from carbazole units to dipyrido[3,2-a:2′,3′-c]phenazine. Similar results were found in
similar carbazole containing rhenium and ruthenium complexes [10, 27, 34, 35]. These
results confirm that antenna substitutes can increase the light harvesting efficiency of Re(I)
complexes. Due to varying ligand field strength caused by the substituents for the present
cases, thermally accessible d–d levels could provide a different nonradiative path for
disposal of the excitation energy in the Re(I) complexes reported here. This behavior is
2
+
well known for derivatives of [Ru(bipy)3] in which the ligand-field strength around the
metal is reduced by steric distortions [36] and it has recently been demonstrated for a
series of Re(I)-tricarbonyl-diimine complexes [37] although a range of other nonradiative
decay pathways are in principle available [37, 38]. These observations also imply that
modification of some diimine rhenium(I) carbonyl complexes with suitable hole-transport-
ing moieties would lead to better phosphorescence performances. In addition, from
quantum efficiency data of the corresponding Re(I) complexes in air-equilibrated and
degassed solutions oxygen can decrease the efficiency greatly.
As already reported for Ir(III) complexes, the phosphorescence lifetime is a key factor
in TTA in OLEDs operation [39]. The excited state lifetimes (τ) of Re(I) complexes,
measured in CH Cl solution and solid state at room temperature support the hypothesis of
2
2
MLCT character of the emitting states. As indicated in figures S13–S16 and table 1, the
lifetime decays are monoexponential or two-exponential in the range of sub-microsecond
scale. Re(I) carbonyl complexes that show multiexponential decay kinetics are known
confirming the existence of two light-emission excited states with comparable energies
ꢀ
1
[
32, 39, 40]. By using the equations ꢀ ¼ ꢀISCfkr=ðkr þ knrÞg and sp ¼ ðkr þ knrÞ , it is
possible to calculate the radiative (k ) and nonradiative (k ) decay rates from ꢀ and τ ,
r
nr
1

9
64
Y.-H. Zhou et al.
Table 1. Absorption and photoluminescence data of ReL1–ReL4 at room temperature.
e
Absorption
Compound Medium (k, nm)
Emission
ꢀ (air/degassed) (%)
Lifetime
s (v ) , ls
k
r
b
c
2
d
3
k, nm
10
ReL1
ReL2
ReL3
ReL4
CH
Solid
CH Cl
Solid
CH Cl
Solid
CH Cl
Solid
2
Cl
2
2
2
2
a276
556
552
582
581
637
633
662
673
0a.11/0.36
0a.17/0.57
0a.20/0.68
0a.26/0.84
1.82 (0.98)
0a.60
1a.07
1a.19
1a.35
1.51, 15.69 (0.99)
1.59, 13.98 (0.99)
1.52, 13.13 (0.99)
1.68, 17.74 (0.99)
2.23 (0.98)
2
a299
2
a239, 275
2
a238, 289, 335, 384
1.92, 15.52 (0.99)
1.72, 11.63 (1.00)
a
Not measured.
The emission spectra are corrected.
b
c
2
s
2
std
Calculated by ꢀs ¼ ꢀstdðIsAstdg Þ=ðIstdAsg Þ using air-equilibrated (ꢀstd ¼ 1:8% or degassed (ꢀstd ¼ 9:4% [Ru
2+
ꢀ
(
bpy)
3
]
2Cl acetonitrile solution as a standard sample; the error in this method is estimated to be approxi-
mately 10% of the measured value.
d
The lifetime decays were measured in air and in the lifetime analysis, the v2 parameter indicates the discrepancy
2
between the observed and the expected values for a certain fitting model. In principle, a v = 1 is the best-fit for
the given data and error bars.
e
r
Radiative rate constant calculated from k = ꢀ=s, where s is s1.
where the intersystem-crossing yield (ꢀISC) is typically assumed to be unitary (1.0) for
metal phosphors with strong heavy-atom effect. All the complexes have quite similar knr
values, while ReL4 has a k higher than those of other complexes.
r
4
. Conclusion
Based on dipyrido[3,2-a:2′,3′-c]phenazine (L1), some derivatives (L2: 10,13-dibromodipyri-
do[3,2-a:2′,3′-c]phenazine, L3: 10-bromo-13-carbazolyl-dipyrido[3,2a:2′,3′c]phenazine,
L4: 10,13-dicarbazolyl-dipyrido[3,2-a:2′,3′-c]phenazine) and their corresponding Re(I)
complexes ReL1–ReL4 were synthesized. All Re(I) complexes show photoluminescent
⁄
emissions in CH Cl solution assigned to dp (Re) →p (diimine) MLCT phosphorescence.
2
2
ReL3 and ReL4 show higher luminescence intensity than ReL1 and ReL2, due to the
carbazole. These observations imply that modification of some of the diimine rhenium(I)
carbonyl complexes with carbazole would lead to better phosphorescence. By comparison of
our materials with carbazole containing Re(I) complexes with good electroluminescent
properties, we believe that due to a better carrier-injection and carrier-transportation balance,
they are potential phosphorescence emitters for improvement of OLEDs’ performance.
Acknowledgments
This study was supported by the National Natural Science Foundation of China (Grant
2
0971067 and 21021062) and the Major State Basic Research Development Program
(2011CB808704).
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