Synthesis and photoluminescence properties of four rhenium(I) complexes based on diimine ligands with oxadiazole/carbazole moiety

Article abstract of DOI:10.1016/j.jphotochem.2010.02.010

By introducing two carrier-transporting moieties (oxadiazole and carbazole) into two diimine ligands (2-(2-pyridine)-benzimidazole and 2,2'-dipyridylamine), respectively, four novel ligands (L1-L4) and their corresponding rhenium(I) complexes (1-4) have been synthesized and characterized by elemental analysis, ¹H NMR and IR spectra. Their photophysical properties, thermal analysis, along with the X-ray crystal structure analysis of L4 and corresponding complex 4 are also described. In absorption spectra, the 2-(2-pyridine)-benzimidazole containing complexes 1, 2 show the intraligand charge-transfer (π→π*(L)) bands and metal-to-ligand charge-transfer dπ(Re)→π*MLCT bands, while the 2,2'-dipyridylamine containing complexes 3, 4 only show the π→π*bands. In the excitation spectra, all the complexes show strong MLCT bands. After excitation of π→π*or MLCT bands, all the four Re(I) complexes exhibit broad bands around 550-560nm due to the Re(I)-based ³MLCT emission. The two complexes 1 (with oxadiazole moiety) and 2 (with carbazole moiety) show the photoluminescence quantum efficiency of 2.0% and 7.5% in solid state, respectively, indicating that the carbazole unit is the better chromophore to enhance the luminescence efficiency of diimine Re(I) complexes than the oxadiazole moiety.

Full text of DOI:10.1016/j.jphotochem.2010.02.010

Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Synthesis and photoluminescence properties of four rhenium(I) complexes
based on diimine ligands with oxadiazole/carbazole moiety
Jing Wua, Hong-Yan Lia, Ling-Chen Kanga, Dong-Ping Lia, Huan-Rong Lib, Xin-Hui Zhoua,
Yan Suia, You-Xuan Zhenga,∗, Jing-Lin Zuoa, Xiao-Zeng Youa
a State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering,
Nanjing University, 22 Hankou Road, Nanjing 210093, PR China
b School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
By introducing two carrier-transporting moieties (oxadiazole and carbazole) into two diimine ligands
(2-(2-pyridine)-benzimidazole and 2,2ꢀ-dipyridylamine), respectively, four novel ligands (L1–L4) and
their corresponding rhenium(I) complexes (1–4) have been synthesized and characterized by elemental
analysis, 1H NMR and IR spectra. Their photophysical properties, thermal analysis, along with the X-ray
crystal structure analysis of L4 and corresponding complex 4 are also described. In absorption spectra, the
2-(2-pyridine)-benzimidazole containing complexes 1, 2 show the intraligand charge-transfer (␲ → ␲*
(L)) bands and metal-to-ligand charge-transfer d␲(Re) → ␲* MLCT bands, while the 2,2ꢀ-dipyridylamine
containing complexes 3, 4 only show the ␲ → ␲* bands. In the excitation spectra, all the complexes show
strong MLCT bands. After excitation of ␲ → ␲* or MLCT bands, all the four Re(I) complexes exhibit broad
bands around 550–560 nm due to the Re(I)-based 3MLCT emission. The two complexes 1 (with oxadiazole
moiety) and 2 (with carbazole moiety) show the photoluminescence quantum efficiency of 2.0% and 7.5%
in solid state, respectively, indicating that the carbazole unit is the better chromophore to enhance the
luminescence efficiency of diimine Re(I) complexes than the oxadiazole moiety.
Received 11 November 2009
Received in revised form 22 January 2010
Accepted 12 February 2010
Available online 21 February 2010
Keywords:
Carrier-transporting moieties
Oxadiazole
Carbazole
Diimine ligands
Rhenium(I) complexes
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
in molecular design [3,16,18,19] to adjust the molecular orbital
energy levels in the Re(I) complexes which are related to the pho-
Since Forrest et al. [1] reported that electrophosphorescent
materials could harvest both singlet and triplet excitons and
endowed organic light-emitting devices (OLEDs) with a potential
internal quantum efficiency of 100%, the electrophosphorescence
of heavy metal complexes has been studied extensively [2,3]. Due
to the distinguished qualities that Re(I) complexes possess such as
photophysical, photochemical, excited state redox properties and
with the aim of further exploring novel phosphorescent materials,
more and more researchers pay considerable attention to this field
[3–14].
However, most of the previously reported phosphorescent Re(I)
complexes used in the OLEDs have the disadvantage of the satura-
tion of emission sites causes the triplet–triplet annihilation, which
leads to low efficiency at high current density [15–17]. There are
two strategies available to manipulate original Re(I) complexes and
to overcome the shortcoming mentioned above: (i) the synthe-
sis of novel diimine ligands with different ligand-field are applied
tochemical, photophysical and electrochemical events, because the
spectroscopic and redox behavior of the Re(I) complexes are ligand
dependent and can be tuned by varying the identity of their chelate
ligands and (ii) the addition of functional groups with electro-
donating or -accepting properties into diimine ligands [17,20–25] is
efficient in improving the capability of OLEDs using the Re(I) com-
plexes as the light-emitting layer and avoiding the triplet–triplet
annihilation because of the steric hindrance effect.
In this article, according to these two methods, we designed four
novel Re(I) complexes employing 2-(2-pyridine)-benzimidazole
and 2,2ꢀ-dipyridylamine as the original diimine ligands and
involving oxadiazole and carbazole moieties which own supe-
rior carrier-transporting ability. So, four ligands of 1-(4-5ꢀ-
phenyl-1,3,4-oxadiazolylphenyl)-2-pyridinylbenzoimidazole (L1),
1-(4-carbazolylphenyl)-2-pyridinylbenzimidazole (L2), N-(4-5ꢀ-
phenyl-1,3,4-oxadiazolyl-phenyl)-2,2ꢀ-dipyridylamine (L3), N-(4-
carbazolylphenyl)-2,2ꢀ-dipyridylamine (L4) and their correspond-
ing Re(I) complexes (1–4) have been synthesized successfully. In
order to investigate the potential application in the OLEDs of the
complexes, their optical and thermal stability are measured and
discussed.
∗
Corresponding author. Tel.: +86 25 83596775; fax: +86 25 83314502.
E-mail address: yxzheng@nju.edu.cn (Y.-X. Zheng).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.02.010

136
J. Wu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
2. Experimental
dure [27,29]. Complexes Re(CO)3Cl(Pybm) (5) and Re(CO)3Cl(Dpya)
(6) were also prepared as reference materials by the same method.
Synthesis of 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole (a): 4-
Bromobenzoyl chloride (21.95 g, 0.1 mol) was added dropwise to a
solution of benzoyl hydrazine (13.62 g, 0.1 mol) and triethylamine
(10.10 g, 0.1 mol) in chloroform (150 mL) at room temperature (RT).
The resulting mixture was stirred for 1 h and then filtered. The col-
lected solid was washed with water and ethanol to give the product
Nꢀ-benzoyl-4-bromobenzohydrazide (30.32 g, yield 95%). A mix-
ture of Nꢀ-benzoyl-4-bromobenzo-hydrazide (20.00 g) and POCl3
(250 mL) in a 500 mL flask was refluxed under nitrogen for 5 h. The
excessive POCl3 was then distilled out, and the residue was poured
into water. The crude solid state product was collected by filtration
and purified by recrystallization from chloroform/hexane to give a
as white needlelike crystals (16.04 g, yield: 85%). M.p.: 164–168 ◦C.
IR (KBr, cm−1): 3060, 1600, 1546, 1474, 1073, 728, 689. 1H NMR
(CDCl3, 500 MHz): ı 8.159 (d, 2H, J = 7 Hz), 8.040 (d, 2H, J = 9 Hz),
7.710 (d, 2H, J = 8.5 Hz), 7.570 (m, 3H). MS (ESI): m/z 301.08 [M]+.
Anal. Calcd. for C14H9N2OBr: C, 55.84; H, 3.01; N, 9.30. Found: C,
55.87; H, 3.11; N, 9.27.
2.1. Materials and instruments
Carbazole was purchased from Yuan Hang Reagent Company
(China). 1,4-Dibromobenzene, 2-(4-bromophenyl)-5-phenyl-
1,3,4-oxadiazole, benzoyl hydrazine, 2-(2-pyridyl)benzimidazole
(Pybm), 2,2ꢀ-dipyridylamine (Dpya), 1,3-dimethyl-3,4,5,6-
terahydro-2(1H)-pyrimidinone
(DMPU)
and
rhenium
pentacarbonyl chloride were brought from Acros, Aldrich and
Alfa Companies. The IR spectra were taken on a Vector22 Bruker
spectrophotometer (400–4000 cm−1) with KBr pellets. NMR spec-
tra were measured on a Bruker AM 500 spectrometer. Mass spectra
were determined with an Autoflex IITM instrument for MALDI-
TOF-MS or on a Varian MAT 311A instrument for ESI-MS. Elemental
analyses for C, H, and N were performed on a PerkinElmer 240C
analyzer. Absorption spectra were measured on a UV-3100 spec-
trophotometer. Photoluminescence measurements were carried
out on Hitachi F4600 luminescence spectrophotometer equipped
with a xenon arc lamp. The photoluminescence lifetime was
measured with an Edinburgh Instruments FLS920P fluorescence
spectrometer and obtained from time-resolved luminescence
experiments at the MLCT excitation and maximal emission wave-
lengths. The quantum yield was determined using an integrating
sphere (150 mm diameter, BaSO4 coating) from Edinburgh Instru-
ments according to the reported procedure [26]. The spectra were
corrected for variations in the output of the excitation source
and for variations in the detector response. The quantum yield
can be defined as the integrated intensity of the luminescence
signal divided by the integrated intensity of the absorption signal.
Only the intense emission bands of the Re(I) complexes around
550 nm was measured by the integrating sphere being excited at
the MLCT bands, but this intensity value was corrected by taking
into account the relative intensity of the other transitions (as
determined from the steady-state luminescence spectrum). In this
way, an intensity value that corresponds to the total luminescence
output was obtained. The absorption intensity was calculated by
subtracting the integrated intensity of the light source with the
sample in the integrating sphere from the integrated intensity of
the light source with a blank sample in the integrating sphere.
The crystals of L4 and 4 suitable for single-crystal X-ray analy-
sis were obtained by slow evaporation of dichloromethane-hexane
solution. The data were collected on a Bruker Smart Apex CCD
diffractometer equipped with graphitemonochromated Mo K␣
(ꢀ = 0.71073 Å) radiation using a ω–2Â scan mode at 293 K. The
highly redundant data sets were reduced using SAINT and absorp-
tion corrections were applied using SADABS supplied by Bruker.
The structures were solved by direct methods and refined by
full-matrix least-squares methods on F2 using SHELXTL-97. Ther-
mogravimetrical and differential thermal analysis (TGA–DTA) was
performed in N2 atmosphere with a flow rate of 100 mL/min on a
simultaneous SDT 2960 thermal analyzer from 20 to 750 ◦C, with a
ramp rate of 10 ◦C/min.
Synthesis of 1-carbazolyl-4-bromobenzene (b): Similar methods
(see Scheme 1) are used to prepare b, L1, L2, L3 and L4. A mix-
ture of carbazole (16.72 g, 0.1 mol), 1,4-dibromobenzene (23.59 g,
0.1 mol), CuI (1.90 g, 0.01 mol), 18-Crown-6 (0.88 g, 0.0033 mol),
K2CO3 (27.67 g, 0.2 mol) and DMPU (3 mL) was put into reactor,
then keep it heating at 170 ◦C for 13 h under nitrogen. After cooling
to room temperature, the mixture was quenched with 1N HCl, the
precipitate was filtered and washed with NH3·H2O and water. The
brown solid was purified with column chromatography using hex-
ane as eluant (10.95 g, yield: 34%). M.p.: 152–154 ◦C. IR (KBr, cm−1):
3056, 1496, 1452, 1230, 751. 1H NMR (CDCl3, 500 MHz): ı 8.175
(d, 2H, J = 7 Hz), 7.757 (d, 2H, J = 8.5 Hz), 7.495 (d, 2H, J = 8.5 Hz),
7.431 (t, 2H, J = 7 Hz), 7.411 (d, 2H, J = 9 Hz), 7.342 (t, 2H, J = 7.5 Hz).
MS (MALDI-TOF): m/z 321.035 [M]+. Anal. Calcd. for C18H12NBr: C,
67.10; H, 3.75; N, 4.35. Found: C, 66.93; H, 3.71; N, 4.31.
Synthesis
of
1-(4-5ꢀ-phenyl-1,3,4-oxadiazolylphenyl)-2-
pyridinylbenzoimidazole (L1): The procedure is similar to that
of compound b with the materials of a (3.01 g, 0.01 mol) and Pybm
(1.95 g, 0.01 mol) at the temperature of 230 ◦C (2.50 g, yield: 60%).
M.p.: 186–189 ◦C. IR (KBr, cm−1): 3050, 1606, 1500, 1442, 1385,
773, 755, 741, 708, 691. 1H NMR (CDCl3, 500 MHz): ı 8.380 (d,
3H, J = 7.5 Hz), 8.200 (d, 2H, J = 7.5 Hz), 7.987 (t, 1H, J = 7.5 Hz),
7.603–7.577 (m, 7H), 7.525 (t, 2H, J = 7.5 Hz), 7.405 (t, 1H, J = 6 Hz),
7.321(d, 1H, J = 8.5 Hz). MS (MALDI-TOF): m/z 416.232 [M]+. Anal.
Calcd. for C26H17N5O: C, 75.17; H, 4.12; N, 16.86. Found: C, 75.11;
H, 4.21; N, 16.81.
Synthesis of 1-(4-carbazolylphenyl)-2-pyridinylbenzimidazole
(L2): The procedure is similar to that of compound b with the
materials of b (3.22 g, 0.01 mol) and Pybm (1.95 g, 0.01 mol) at the
temperature of 230 ◦C (2.93 g, yield: 67%). M.p.: 225–228 ◦C. IR
(KBr, cm−1): 3044, 1728, 1593, 1514, 1446, 740. 1H NMR (CDCl3,
500 MHz): ı 8.489 (d, 2H, J = 4.5 Hz), 8.203 (d, 2H, J = 7.5 Hz), 8.074
(d, 1H, J = 8 Hz), 7.906 (t, 1H, J = 7.5 Hz), 7.762 (d, 2H, J = 8.5 Hz),
7.614 (d, 2H, J = 9 Hz), 7.550 (d, 2H, J = 7.5 Hz), 7.502 (t, 3H, J = 7 Hz),
7.472 (m, 2H), 7.357 (t, 3H, J = 7 Hz). MS (MALDI-TOF): m/z 437.130
[M]+. Anal. Calcd. for C30H20N4: C, 82.55; H, 4.62; N, 12.84. Found:
C, 82.54; H, 4.69; N, 12.83.
2.2. Synthesis
The chemical structures of the materials used in this work
and the synthetic routes were depicted in Scheme 1. The
ligand precursors 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole
(a) and 1-carbazolyl-4-bromobenzene (b) were synthesized as
described in literature [27,28]. The four ligands of 1-(4-5ꢀ-
phenyl-1,3,4-oxadiazolylphenyl)-2-pyridinylbenzoimidazole (L1),
1-(4-carbazolyl-phenyl)-2-pyridinylbenzimidazole (L2), N-(4-5ꢀ-
phenyl-1,3,4-oxadiazolyl-phenyl)-2,2ꢀ-dipyridylamine (L3), N-(4-
carbazolylphenyl)-2,2ꢀ-dipyridylamine (L4) and the corresponding
Re(I) complexes of 1–4 were prepared according to modified proce-
Synthesis
of
N-(4-5ꢀ-phenyl-1,3,4-oxadiazolylphenyl)-2,2ꢀ-
dipyridylamine (L3): The procedure is similar to that of compound
b with the materials of a (3.01 g, 0.01 mol) and Dpya (1.71 g,
0.01 mol) at the temperature of 180 ◦C (2.31 g, yield: 59%). M.p.:
136–140 ◦C. IR (KBr, cm−1): 2994, 1588, 1496, 1467, 1332, 772,
740, 708, 685. 1H NMR (CDCl3, 500 MHz): ı 8.573 (m, 2H), 8.217
(d, 2H, J = 8.5 Hz), 8.149 (d, 2H, J = 8 Hz), 7.755 (t, 2H, J = 7.5 Hz),
7.578 (m, 3H), 7.392 (d, 2H, J = 8.5 Hz), 7.158 (m, 2H), 7.021 (d,
2H, J = 8 Hz). MS (MALDI-TOF): m/z 392.169 [M]+. Anal. Calcd. for

J. Wu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
137
230–232 ◦C. IR (KBr, cm−1): 2924, 2020, 1904, 1880, 754. 1H NMR
(CDCl3, 500 MHz): ı 9.206 (d, 1H, J = 5 Hz), 8.608 (d, 1H, J = 8 Hz),
8.535 (d, 1H, J = 9 Hz), 8.226 (t, 3H, J = 9.5 Hz), 7.808 (m, 3H), 7.638
(m, 4H), 7.559 (m, 2H), 7.215 (d, 1H, J = 8.5 Hz), 7.175 (d, 1H,
J = 8.5 Hz). MS (MALDI-TOF): m/z 686.162 [M−Cl]+. Anal. Calcd. for
C29H17N5O4ClRe: C, 48.30; H, 2.38; N, 9.71. Found: C, 48.27; H, 2.37;
N, 9.72.
Synthesis of 2: The procedure is similar to that of 1 (0.26 g, yield:
70%). M.p.: >300 ◦C. IR (KBr, cm−1): 2017, 1905 (b), 750. 1H NMR
(CDCl3, 500 MHz): ı 9.227 (d, 1H, J = 6 Hz), 8.235 (t, 3H, J = 7 Hz),
8.046 (t, 2H, J = 7.5 Hz), 7.879 (m, 3H), 7.652 (m, 3H), 7.576 (m, 4H),
7.430 (t, 2H, J = 7.5 Hz), 7.322 (m, 2H). MS (MALDI-TOF): m/z 717.67
[M−Cl]+. Anal. Calcd. for C33H20N4O3ClRe: C, 53.40; H, 2.72; N, 7.55.
Found: C, 53.27; H, 2.87; N, 7.54.
C24H17N5O: C, 73.64; H, 4.38; N, 17.89. Found: C, 73.67; H, 4.31; N,
17.97.
Synthesis of N-(4-carbazolylphenyl)-2,2ꢀ-dipyridylamine (L4): The
procedure is similar to that of compound b with the materials of
b (3.22 g, 0.01 mol) and Dpya (1.71 g, 0.01 mol) at the temperature
of 180 ◦C (3.71 g, yield: 90%). M.p.: >290 ◦C. IR (KBr, cm−1): 3040,
1582, 1512, 1458, 1442, 1320, 754. 1H NMR (CDCl3, 500 MHz): ı
8.595 (m, 2H), 8.174 (d, 2H, J = 7.5 Hz), 7.753 (m, 2H), 7.695 (d, 2H,
J = 7 Hz), 7.564 (d, 2H, J = 8 Hz), 7.487 (m, 4H), 7.323 (t, 2H, J = 7 Hz),
7.122 (m, 2H), 7.063 (d, 2H, J = 8 Hz). MS (MALDI-TOF): m/z 412.234
[M]+. Anal. Calcd. for C28H20N4: C, 81.53; H, 4.89; N, 13.58. Found:
C, 81.44; H, 4.83; N, 13.57.
Synthesis of 1: L1 (0.21 g, 0.5 mmol) and Re(CO)5Cl (0.18 g,
0.5 mmol) were refluxed in 30 mL of anhydrous toluene for 6 h.
After the mixture was cooled to RT, the solvent was distilled
out. The resulting yellow solid was purified by silica gel column
chromatography with dichloromethane and hexane (v/v = 2:1, 5%
in volume Et3N was added) to get 1 (0.25 g, yield: 70%). M.p.:
Synthesis of 3: The procedure is similar to that of 1 (0.28 g, yield:
79%). M.p.: 218–220 ◦C. IR (KBr, cm−1): 2020, 1896 (b), 1433, 779,
732, 714. 1H NMR (CDCl3, 500 MHz): ı 9.104 (d, 2H, J = 7 Hz), 8.245
(d, 2H, J = 9 Hz), 8.152 (d, 2H, J = 8.5 Hz), 7.994 (t, 2H, J = 8 Hz), 7.597
Scheme 1. Synthetic routes for a, b, L1–L4 and 1–6. (i) Et3N, CHCl3, RT; (ii) POCl3, reflux; (iii) CuI, 18-Crown-6, K2CO3, DMPU, in reactor; (iv) Re(CO)5Cl, toluene, reflux.

138
J. Wu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
(m, 6H), 7.405 (m, 5H). MS (MALDI-TOF): m/z 662.125 [M−Cl]+.
Anal. Calcd. for C27H17N5O4ClRe: C, 46.52; H, 2.46; N, 10.05. Found:
C, 46.47; H, 2.46; N, 10.01.
Table 1
Crystallographic data for L4 and 4.
L4
4
Synthesis of 4: The procedure is similar to that of 1 (0.23 g, yield:
63%). M.p.: >290 ◦C. IR (KBr, cm−1): 2018, 1909, 1889, 749. 1H NMR
(CDCl3, 500 MHz): ı 9.048 (m, 2H), 8.209 (d, 2H, J = 7.5 Hz), 7.896 (m,
2H), 7.852 (d, 2H, J = 8.5 Hz), 7.800 (d, 2H, J = 8.5 Hz), 7.530–7.441 (m,
7H), 7.369 (t, 3H, J = 7 Hz). MS (MALDI-TOF): m/z 683.132 [M−Cl]+.
Anal. Calcd. for C31H20N4O3ClRe: C, 51.84; H, 2.81; N, 7.80. Found:
C, 51.81; H, 2.84; N, 7.87.
Formula
FW
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C28H20N4
412.49
291(2)
0.71073
Orthorhombic
Fdd2
15.309(3)
14.380(3)
19.508(5)
90.00
90.00
90.00
4294.6(17)
1
1.276
0.077
1728
2.1–20.4
5184
1813
1813/1/148
0.912
0.0528, 0.1200
0.1054, 0.1563
736721
C31H20ClN4O3Re
718.16
291(2)
0.71073
Triclinic
P-1
10.5233(16)
14.873(2)
17.719(3)
87.012(2)
88.711(2)
79.754(2)
2725.1(7)
4
1.750
4.598
1400
1.85–25.00
13908
9487
9487/0/721
0.780
0.0526, 0.0979
0.1009, 0.1105
729550
b (Å)
c (Å)
˛ (◦)
ˇ (◦)
3. Results and discussion
ꢁ (◦)
V (Å3)
3.1. Crystallography
Z
ꢂcalcd (g/cm3)
ꢃ (Mo K␣) (mm−1
F (0 0 0)
)
The crystallographic data for the L4 and 4 support the struc-
tures of these compounds. The crystal data are presented in Table 1
and selected bond distances and angles for the compounds are
listed in Table 2. With respect to the L4 (Fig. 1), the length of the
C(9)–N(2) bond connecting carbazole group and the benzene ring is
1.437(8) Å. The C(10)–N(2)–C(9) bond angle is 125.8(3)◦. The bond
C(6)–N(1) between the benzene ring and Dpya is 1.429(9) Å. The
C(5)–N(1)–C(6) bond angle is 120.6(3)◦. Carbazole group and the
benzene ring are not coplanar with a dihedral angle of 49.19◦.
An ORTEP diagram of 4 is also shown in Fig. 1. The coordination
geometry at the Re atom is a distorted octahedron with the three
carbonyl ligands arranged in a facial fashion. The distances of C(29),
C(30) and C(31) to Re(1) are 1.88(1) Å averagely and the average
Re–N bond length is 2.160(8) Å. All the bond distance data are in
agreement with analogous Re(I) diimine complexes [16,30]. The
C–Re–C bond angels are in the range of 86.0(5)–89.7(4)◦, which is
close to 90◦, the O–C–Re bond angels are close to 180◦ indicating
that CO ligands are linearly coordinated, while the N–Re–N bond
angle is 80.9(3)◦, which is much less than 90◦, this is possibly due
to the steric requirement of the bidentate coordination of the L4
ligand.
Range of transm factors (◦)
Reflns collected
Unique
Data/restraints/params
GOF on F2
R1a , wR2b [I > 2ꢄ(I)]
R1a , wR2b (all data)
CCDC No.
R1a
=
||Fo|| − ||Fc||/ Fo|.
wR2b = [ w(Fo2 − Fc2)2/ w(Fo2)]1/2
.
ands are similar in shape, belonging to the ␲ → ␲* transitions of
carrier-transporting moieties and Pybm/Dpya. The excitation spec-
tra of all the complexes (Fig. 3b) measured by monitoring the
respective emission ꢀmax are also similar in shape to each other.
The bands are centered at around 468 nm with weaker shoul-
ders which are assigned to MLCT transitions as depicted above.
However, the excitation spectrum of 4 is unusual. The stronger
band sites at shorter wavelength about 400 nm, in opposite, the
intensity of longer wavelength excitation is weaker. By compar-
ing the excitation spectra of free ligands with their corresponding
complexes, it is worthy to note that the excitation spectra of
the complexes gain red shift. The emission spectra of complexes
centralize at around 550–560 nm upon being excited with the
3.2. Photophysical properties
The UV–vis absorption spectra of the L1–L4 and corresponding
Re(I) complexes 1–4 are exhibited in Fig. 2. For all of the Re(I) com-
plexes, the dominant absorption bands in the 230–350 nm region
are assigned to the intraligand charge-transfer (␲ → ␲* (L)) tran-
sition by comparing with their corresponding free ligands, this
rule is common in most Re(I) complexes [31]. We can see the
absorptions at longer wavelength for 1 and 2 extend to visible
region from 350 to 500 nm with weaker intensities. The metal-
to-ligand charge-transfer d␲ (Re) → ␲* (N–N) MLCT is tentatively
accounted for these bands [32,10,33]. By comparing the bands of
the four Re(I) complexes, we can also find that the charge-transfer
d␲ (Re) → ␲* (N–N) bands of 1 and 2 are more evident than the
later two complexes. For comparison, the UV–vis absorption spec-
tra of two complexes 5 and 6 without functional moieties are also
presented in Fig. 2. From Fig. 2a we can find that after adding car-
bazole/oxidazole moiety to Pybm, the higher-energy absorption
peaks of derived Re-complexes shifted to longer wavelength. This
phenomenon can be explained as follows: the structure of Pybm
is rigid, the conjugated plate of derived ligands was enlarged, and
the energy of LUMO becomes lower. While the structure of Dpya is
flexible, the additional moieties have no evident influence on the
conjugated plate, so the corresponding absorption peaks of 3, 4 and
6 have no remarkable change (Fig. 2b).
Table 2
Selected bond lengths (Å) and angles (◦) for L4 and 4.
L4a
4
C(4)–N(3)
C(5)–N(3)
C(5)–N(1)
C(6)–N(1)
C(9)–N(2)
C(10)–N(2)
N(3)–C(4)–C(3)
N(3)–C(5)–C(1)
N(3)–C(5)–N(1)
C(1)–C(5)–N(1)
C(7)–C(6)–N(1)
C(8)–C(9)–N(2)
N(2)–C(10)–C(15)
N(2)–C(10)–C(11)
C(5)–N(1)–C(5A)
C(5)–N(1)–C(6)
C(10)–N(2)–C(10A)
C(10)–N(2)–C(9)
C(5)–N(3)–C(4)
1.331(6)
1.329(6)
1.406(6)
1.429(9)
1.437(8)
1.385(5)
Re(1)–C(29)
Re(1)–C(30)
Re(1)–C(31)
Re(1)–N(3)
Re(1)–N(4)
Re(1)–Cl(1)
1.87(1)
1.88(1)
1.89(1)
2.157(8)
2.163(8)
2.485(3)
89.7(4)
88.7(5)
86.0(5)
94.5(4)
174.8(4)
97.0(4)
92.3(4)
96.0(4)
177.8(4)
80.9(3)
177.8(3)
90.9(3)
93.5(3)
84.7(2)
85.4(2)
123.2(5)
C(29)–Re(1)–C(30)
C(29)–Re(1)–C(31)
C(30)–Re(1)–C(31)
C(29)–Re(1)–N(3)
C(30)–Re(1)–N(3)
C(31)–Re(1)–N(3)
C(29)–Re(1)–N(4)
C(30)–Re(1)–N(4)
C(31)–Re(1)–N(4)
N(3)–Re(1)–N(4)
C(29)–Re(1)–Cl(1)
C(30)–Re(1)–Cl(1)
C(31)–Re(1)–Cl(1)
N(3)–Re(1)–Cl(1)
N(4)–Re(1)–Cl(1)
O(1)–C(29)–Re(1)
O(2)–C(30)–Re(1)
O(3)–C(31)–Re(1)
121.6(5)
116.7(4)
121.7(5)
120.6(3)
119.4(3)
129.2(4)
109.2(4)
118.9(6)
120.6(3)
108.4(5)
125.8(3)
118.0(4)
173.6(10)
176.7(11)
175.4(11)
Fig. 3 and Table 3 show photoluminescence properties of the
L1–L4 and 1–4 in solid state under ambient conditions. From
Fig. 3a it can be found that the major excitation bands of lig-
a
Symmetry code: 7/4 + x, 9/4 − y, 3/4 + z.

J. Wu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
139
Fig. 1. ORTEP view of L4 (symmetry code: 7/4 + x, 9/4 − y, 3/4 + z) and 4 with the atom-numbering scheme. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn at
the 30% probability level.
Fig. 2. UV–vis absorption of L1–L4 and 1–6 in CH2Cl2 solution at room temperature.
maximum excitation peaks are characteristic of Re(I)-based MLCT
emission frequently found in Re(CO)3ClL (L = polypyridine) com-
plexes [32]. It also exhibits that the emission spectra of 1 and 2
are more intense than the later two complexes, this could be due
to more rigid structure of Pybm type complexes compared with
that of Dypa ones. Ward et al. [34] reported that the coordination
ring of the ligand with Re(I) also can affect the luminescence. In
the Dypa type complexes, coordination of the ligand at the Re(I)
centre takes place with formation of a 6-membered chelate ring
(see above), as opposed to a 5-membered one for Pybm type lumi-
nescent Re(I) complexes [35–39]. This is likely to result in a lower
ligand-field strength for the present cases. As a consequence, lower-
lying, thermally accessible d–d MC levels could provide an efficient
non-radiative path for disposal of the excitation energy in the Re(I)
complexes reported here. This behavior is well known for deriva-
tives of [Ru(bipy)3]2+ in which the ligand-field strength around the
metal is reduced by steric distortions [40–43] and has recently been
demonstrated for a range of Re(I)-tricarbonyl-diimine complexes
[44] although it should be noted that a range of other non-radiative
decay pathways are in principle available [44,45].
The supposed nature of the emitting states is also supported
by the corresponding radiative decays which lie in the microsec-
ond timescale domain typical for MLCT and IL transitions. The
luminescence decay curves of all the complexes were obtained
Table 3
The photoluminescence data of Re(I) complexes at room temperature in solid state.
Complex
Excitation
Emission
Lifetime (␮s)d
ꢀ, nm
ꢀmax, nma,b
ꢅ (%)c
2.0
ꢆ1
ꢆ2
1
2
3
4
373, 441, 494
370, 442, 490
380, 406, 438
400
565
562
432, 514, 547
426, 547, 595
1.48 (52.45%)
1.67 (47.49%)
1.48 (51.00%)
1.46 (53.18%)
13.13 (47.55%)
10.62 (52.51%)
12.15 (49.00%)
13.91 (46.82%)
7.5
e
e
a
Emission maxima from not corrected spectra.
Excited by the highest excitation peak.
Obtained from time-resolved luminescence experiments at the MLCT excitation and maximal emission wavelengths.
Be detected at the excitation wavelength is 468 nm, and the emission is monitored at their MLCT emission peaks around 550 nm in solid state.
Not detected.
b
c
d
e

140
J. Wu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
Fig. 3. (a) Excitation and emission spectra of L1–L4 in solid state; (b) excitation and emission spectra of 1–4 in solid state. All the spectra were measured under ambient
conditions.
from time-resolved luminescence experiments at the MLCT exci-
tation and maximal emission wavelengths. As indicated in Fig. 4
and Table 3, the decay curves of all complexes measured in solid
state are composed of two exponential decays with lifetimes of
1.32–1.67 ␮s (∼50%) and 10.62–14.84 ␮s (∼50%) [46–48]. The Re(I)
carbonyl complexes that show multiexponential decay kinetics are
known, confirming the existence of two light-emission excited
states with comparable energies [46–48]. The long-lived compo-
nent is thus assigned to the emission from the ␲–␲* state and
the shorter-lived component is assigned to the emission from the
MLCT state. In general, if there is potential surface crossing from
the higher ligand ␲–␲* state to the lower MLCT state, one can
expect, on the basis of the energy gap law, a shorter decay life-
time of the ␲–␲* state than the lower MLCT state [46–48]. We
Fig. 4. Photoluminescence lifetime decay measurement of 1–4 in solid state at room temperature. The excitation wavelength is 468 nm, and the emission is monitored at
their MLCT emission peaks around 550 nm.

J. Wu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
141
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (Grant 20701019, 20971067 and 20721002),
the Natural Science Foundation of Jiangsu Province (Grant
BK2008257), the Major State Basic Research Development Program
(2006CB806104 and 2007CB925103) and the Research Fund for the
Doctoral Program of Higher Education (Grant 20070284053).
References
[1] M.A. Baldo, D.F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M.E. Thompson, S.R.
Forrest, Highly efficient phosphorescent emission from organic electrolumi-
nescent devices, Nature 395 (1998) 151–154.
[2] H.J. Bolink, L. Cappelli, E. Coronado, M. Grätzel, E. Ortí, R.D. Costa, P.M. Viruela,
M.K. Nazeeruddin, Stable single-layer light-emitting electrochemical cell using
4,7-diphenyl-1,10-phenanthroline-bis(2-phenylpyridine)iridium(III) hexaflu-
orophosphate, J. Am. Chem. Soc. 128 (2006) 14786–14787.
[3] Y. Li, Y. Wang, Y. Zhang, Y. Wu, J. Shen, Carbonyl polypyridyl Re(I) com-
plexes as organic electroluminescent materials, Synth. Met. 99 (1999) 257–
260.
[4] K.K.W. Lo, K.H.K. Tsang, N. Zhu, Luminescent tricarbonylrhenium(I) polypyri-
dine estradiol conjugates: synthesis, crystal structure, and photophysical,
electrochemical, and protein-binding properties, Organometallics 25 (2006)
3220–3227.
Fig. 5. TGA traces for the 1–4.
[5] M. Busby, P. Matousek, M. Towrie, I.P. Clark, M. Motevalli, F. Hartl, A.
Vlcˇek Jr., Rhenium-to-benzoylpyridine and rhenium-to-bipyridine MLCT
excited states of fac-[Re(Cl)(4-benzoylpyridine)(2)(CO)(3)] and fac-[Re(4-
benzoylpyridine)(CO)(3)(bpy)](+): a time-resolved spectroscopic and spectro-
electrochemical study, Inorg. Chem. 43 (2004) 4523–4530.
further probed the photophysical properties of 1 and 2 by mea-
suring their photoluminescence quantum efficiency in solid state
using an integrating sphere (150 mm diameter, BaSO4 coating)
from Edinburgh Instruments according to the reported procedure
[26], the data are 2.0% and 7.5%, respectively. The data are agree
with the luminescence intensity sequence in Fig. 3 indicating the
carbazole unit is the better chromophore to enhance the lumines-
cence efficiency of diimine Re(I) complexes than oxadiazole moiety
in our cases. This function of carbazole unit has been reported in
literature [49,50].
+
[6] L. Wei, J.W. Babich, W. Ouellette, J. Zubieta, Developing the {M(CO)3} core
for fluorescence applications: rhenium tricarbonyl core complexes with ben-
zimidazole, quinoline, and tryptophan derivatives, Inorg. Chem. 45 (2006)
3057–3066.
[7] H. Tsubaki, A. Sekine, Y. Ohashi, K. Koike, H. Takeda, O. Ishitani, Control of pho-
tochemical, photophysical, electrochemical, and photocatalytic properties of
rhenium(I) complexes using intramolecular weak interactions between lig-
ands, J. Am. Chem. Soc. 127 (2005) 15544–15555.
[8] N. Marti, B. Spingler, F. Breher, R. Schibli, Comparative studies of substitu-
tion reactions of rhenium(I) dicarbonyl-nitrosyl and tricarbonyl complexes in
aqueous media, Inorg. Chem. 44 (2005) 6082–6091.
[9] A. Gabrielsson, F. Hartl, H. Zhang, J.R. Lindsay Smith, M. Towrie, A. Vlcˇek Jr.,
R.N. Perutz, Ultrafast charge separation in a photoreactive rhenium-appended
porphyrin assembly monitored by picosecond transient infrared spectroscopy,
J. Am. Chem. Soc. 128 (2006) 4253–4266.
3.3. Thermal analysis
[10] B.J. Coe, N.R.M. Curati, E.C. Fitzgerald, S.J. Coles, P.N. Horton, M.E. Light, M.B.
Hursthouse, Syntheses and properties of bimetallic chromophore-quencher
assemblies containing ruthenium(II) and rhenium(I) centers, Organometallics
26 (2007) 2318–2329.
[11] D.L. Reger, R.P. Watson, M.D. Smith, P.J. Pellechia, Bitopic phenylene-linked
bis(pyrazolyl)methane ligands: preparation and supramolecular structures of
hetero- and homobimetallic complexes incorporating organoplatinum(II) and
tricarbonylrhenium(I) centers, Organometallics 24 (2005) 1544–1555.
[12] S.C.F. Lam, V.W.W. Yam, K.M.C. Wong, E.C.C. Cheng, N. Zhu, Synthesis
and characterization of luminescent rhenium(I)–platinum(II) polypyridine
bichromophoric alkynyl-bridged molecular rods, Organometallics 24 (2005)
4298–4305.
[13] A. Albertino, C. Garino, S. Ghiani, R. Gobetto, C. Nervi, L. Salassa, E. Rosenberg,
A. Sharmin, G. Viscardi, R. Buscaino, G. Croce, M. Milanesio, Photophys-
ical properties and computational investigations of tricarbonylrhenium(I)
[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]L and tricarbonylrhenium(I)[2-
(benzo[d]-X-azol-2-yl)-4-methylquinoline]L derivatives (X = N-CH3, O, or S;
L = Cl−, pyridine), J. Organomet. Chem. 692 (2007) 1377–1391.
[14] V.W.W. Yam, W.Y. Lo, C.H. Lam, W.K.M. Fung, K.M.C. Wong, V.C.Y. Lau, N. Zhu,
Synthesis and luminescence behavior of mixed-metal rhenium(I)–copper(I)
and –silver(I) alkynyl complexes, Coord. Chem. Rev. 245 (2003) 39–47.
[15] V.W.W. Yam, B. Li, Y. Yang, B.W.K. Chu, K.M.C. Wong, K.K. Cheung, Preparation,
photo-luminescence and electro-luminescence behavior of Langmuir–Blodgett
Films of bipyridylrhenium(I) surfactant complexes, Eur. J. Inorg. Chem. 25
(2003) 4035–4042.
[16] K. Wang, L. Huang, L. Gao, L. Jin, C. Huang, Synthesis, crystal structure, and pho-
toelectric properties of Re(CO)3ClL (L = 2-(1-ethylbenzimidazol-2-yl)pyridine),
Inorg. Chem. 41 (2002) 3353–3358.
[17] B. Li, M. Li, Z. Hong, W. Li, T. Yu, H. Wei, Observation of red intraligand elec-
trophosphorescence from a stilbene-containing Re(I) complex, Appl. Phys. Lett.
85 (2004) 4786–4788.
[18] F. Li, G. Cheng, Y. Zhao, J. Feng, S. Liu, M. Zhang, Y. Ma, J. Shen, White-
electrophosphorescence devices based on rhenium complexes, Appl. Phys. Lett.
83 (2003) 4716–4718.
[19] G. David, P.J. Walsh, K.C. Gordon, Red electroluminescence from transparent
PVK-dye films based on dipyrido[3,2-a:20,30-c]phenazine and Re(CO)3Cl-
dipyrido[3,2-a:20,30-c]phenazine dyes, Chem. Phys. Lett. 383 (2004)
292–296.
In order to investigate the stable characteristics of all the four
Re(I) complexes, TGA was performed on them in a N2 atmosphere,
and the traces are presented in Fig. 5. Complex 1 began to lose
weight when the temperature reached at 322 ◦C, the loss of the
chlorine anion and carbonyl groups can account for this. 2, 3 and 4
show the similar thermal characteristics as 1 in a N2 atmosphere:
they began to decompose for the same reason at 374, 302 and
356 ◦C, respectively. 3 shows another weight loss at 149 ◦C possibly
due to that the sample is not dry enough, it lost water at this tem-
perature. The weight loss at the temperature higher than 400 ◦C is
probably caused by the unassisted thermolysis of ligands or simply
its sublimation.
4. Conclusion
We have synthesized four novel ligands and their corresponding
Re(I) complexes with oxadiazole or carbazole moiety successfully.
All the Re(I) complexes exhibit better photoluminescent properties
in solid state than those without functional moieties. It also exhibits
that the emission spectra of 1 and 2 are more intense than 3 and 4,
this could be due to more rigid structure of Pybm type complexes
compared with that of Dypa ones. Besides that, the carbazole con-
taining complex 2 shows higher quantum efficiency (7.5%) in solid
state than the oxadiazole containing complex 1 (2.0%) indicating
the carbazole unit is the better chromophore to enhance the lumi-
nescence properties of diimine Re(I) complexes than oxadiazole
moiety.

142
J. Wu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 135–142
[20] C. Fu, M. Li, Z. Su, Z. Hong, W. Li, B. Li, Improved performance of electrophos-
phorescent devices based on Re(CO)3Cl-dipyrido[3,2-a:2ꢀ,3ꢀ-c]phenazine, Appl.
Phys. Lett. 88 (2006) 093507–093509.
[37] W.M. Xue, N. Goswami, D.M. Eichhorn, P.L. Orizondo, D.P. Rillema, synthe-
sis and luminescence properties of a nonsymmetrical ligand-bridged ReI–ReI
chromophore, Inorg. Chem. 39 (2000) 4460–4467.
[21] F. Li, M. Zhang, G. Cheng, J. Feng, Y. Zhao, Y. Ma, S. Liu, J. Shen, Highly efficient
electrophosphorescence devices based on rhenium complexes, Appl. Phys. Lett.
84 (2004) 148–150.
[22] X. Gong, P.K. Ng, W.K. Chan, Trifunctional light-emitting molecules based
on rhenium and ruthenium bipyridine complexes, Adv. Mater. 10 (1998)
1337–1340.
[23] Y. Li, Y. Liu, J. Guo, F. Wu, W. Tian, B. Li, Y. Wang, Photoluminescent and electro-
luminescent properties of phenol-pyridine beryllium and carbonyl polypyridyl
Re(I) complexes codeposited films, Synth. Met. 118 (2001) 175–179.
[24] F. Li, M. Zhang, J. Feng, G. Cheng, Z. Wu, Y. Ma, S. Liu, Red electrophospho-
rescence devices based on rhenium complexes, Appl. Phys. Lett. 83 (2003)
365–367.
[38] K.A. Walters, K.D. Ley, C.S.P. Cavalaheiro, S.E. Miller, D. Gosztola, M.R.
Wasielewski, A.P. Bussandri, H. van Willigen, K.S. Schanze, photophysics of
␲-conjugated metal–organic oligomers: aryleneethynylenes that contain the
(bpy)Re(CO)3Cl chromophore, J. Am. Chem. Soc. 123 (2001) 8329–8342.
[39] V.W.W. Yam, K.M.C. Wong, S.H.F. Chong, V.C.Y. Lau, S.C.F. Lam, L.J. Zhang, K.K.
Cheung, Synthesis, electrochemistry and structural characterization of lumi-
nescent rhenium(I) monoynyl complexes and their homo- and hetero-metallic
binuclear complexes, J. Organomet. Chem. 670 (2003) 205–220.
[40] R.H. Fabian, D.M. Klassen, R.W. Sonntag, Synthesis and spectroscopic character-
ization of ruthenium and osmium complexes with sterically hindering ligands.
3. Tris complexes with methyl- and dimethyl-substituted 2,2ꢀ-bipyridine and
1,10-phenanthroline, Inorg. Chem. 19 (1980) 1977–1982.
[25] W.K. Chan, P.K. Ng, X. Gong, S. Hou, Light-emitting multifunctional rhenium (I)
and ruthenium (II) 2,2ꢀ-bipyridyl complexes with bipolar character, Appl. Phys.
Lett. 75 (1999) 3920–3922.
[26] P. Lenaerts, K. Driesen, R. Van Deun, K. Binnemans, Covalent coupling of
luminescent tris(2-thenoyltrifluoro acetonato)lanthanide(III) complexes on a
merrifield resin, Chem. Mater. 17 (2005) 2148–2154.
[41] J.M. Kelly, C. Long, C.M. O’Connell, J.G. Vos, A.H.A. Tinnemenans, Preparation,
spectroscopic characterization, and photochemical and electrochemical prop-
erties of some bis(2,2ꢀ-bipyridyl)ruthenium(II) and tetracarbonyltungsten(0)
complexes of 6-p-tolyl-2,2ꢀ-bipyridyl and of 6-p-styryl-2,2ꢀ-bipyridyl and its
copolymers, Inorg. Chem. 22 (1983) 2818–2824.
[42] E.C. Constable, M.J. Hannon, A.M.W. Cargill Thompson, D.A. Tocher, J.V. Walker,
[27] Q. Zhang, J.S. Chen, Y.X. Cheng, L.X. Wang, D.G. Ma, X.B. Jing, F.S. Wang, Novel
hole-transporting materials based on 1,4-bis(carbazolyl)benzene for organic
light-emitting devices, J. Mater. Chem. 14 (2004) 895–900.
[28] Z. Peng, Z. Bao, M.E. Galvin, Oxadiazole-containing polymers for light-emitting
diodes, Adv. Mater. 10 (1998) 680–684.
A principle for the assembly of novel mononuclear building blocks for
supramolecular chemistry, Supramol. Chem. 2 (1993) 243–246.
[43] A.M. Barthram, M.D. Ward, A. Gessi, N. Armaroli, L. Flamigni, F. Barigelletti,
Spectroscopic, luminescence and electrochemical studies on a pair of isomeric
complexes [(bipy)2Ru(AB)PtCl2][PF6]2 and [Cl2Pt(AB)Ru(bipy)2][PF6]2, where
AB is the bis-bipyridyl bridging ligand 2,2ꢀ:3ꢀ,2ꢀꢀ:6ꢀꢀ,2ꢀꢀꢀ-quaterpyridine, New J.
Chem. 22 (1998) 913–917.
[29] J.V. Caspar, T.J. Meyer, Application of the energy gap law to nonradiative,
excited-state decay, J. Phys. Chem. 87 (1983) 952–957.
[30] T. Rajendran, B. Manimaran, F.Y. Lee, G.H. Lee, S.M. Peng, C.C. Wang, K.L.
Lu, First light-emitting neutral molecular rectangles, Inorg. Chem. 39 (2000)
2016–2017.
[31] Z.J. Si, J. Li, B. Li, F.F. Zhao, S.Y. Liu, W.L. Li, Synthesis, structural characterization,
and electrophosphorescent properties of rhenium(I) complexes containing
carrier-transporting groups, Inorg. Chem. 46 (2007) 6155–6163.
[32] W. Liu, R. Wang, X.H. Zhou, J.L. Zuo, X.Z. You, Syntheses, structures, and
properties of tricarbonyl rhenium(I) heteronuclear complexes with a new
bridging ligand containing coupled bis(2-pyridyl) and 1,2-dithiolene units,
Organometallics 27 (2008) 126–134.
[44] K. Koike, N. Okoshi, H. Hori, K. Takeuchi, O. Ishitani, H. Tsubaki, I.P. Clark, M.W.
George, F.P.A. Johnson, J.J. Turner, Mechanism of the photochemical ligand
substitution reactions of fac-[Re(bpy)(CO)3(PR3)]+ complexes and the prop-
erties of their triplet ligand-field excited states, J. Am. Chem. Soc. 124 (2002)
11448–11455.
[45] L.A. Worl, R. Duesing, P. Chen, L.D. Ciana, T.J. Meyer, Photophysical properties
of polypyridyl carbonyl complexes of rhenium(I), J. Chem. Soc., Dalton Trans.
(1991) 849–858.
[46] J.R. Shaw, R.H. Schmehl, Photophysical properties of rhenium(I) diimine com-
plexes: observation of room-temperature intraligand phosphorescence, J. Am.
Chem. Soc. 113 (1991) 389–394.
[47] L. Wallace, D.P. Rillema, Photophysical properties of rhenium(I) tricarbonyl
complexes containing alkyl- and aryl-substituted phenanthrolines as ligands,
Inorg. Chem. 32 (1993) 3836–3843.
[33] R. Kirgan, M. Simpson, C. Moore, J. Day, L. Bui, C. Tanner, D.P. Rillema, Synthe-
sis, characterization, photophysical, and computational studies of rhenium(I)
tricarbonyl complexes containing the derivatives of bipyrazine, Inorg. Chem.
46 (2007) 6464–6472.
[34] N.M. Shavaleev, A. Barbieri, Z. Bell, M.D. Ward, F. Barigelletti, New ligands in
the 2,2ꢀ-dipyridylamine series and their Re(I) complexes; synthesis, structures
and luminescence properties, New J. Chem. 28 (2004) 398–405.
[35] M.D. Ward, F. Barigelletti, Control of photoinduced energy transfer between
metal-polypyridyl luminophores across rigid covalent, flexible covalent,
or hydrogen-bonded bridges, Coord. Chem. Rev. 216–217 (2001) 127–
154.
[48] D.R.
Striplin,
G.A.
Crossby,
Photophysical
investigations
of
rhenium(I)Cl(CO)3(phenanthroline) complexes, Coord. Chem. Rev. 211
(2001) 163–175.
[49] X.H. Li, J. Gui, H. Yang, W.J. Wu, F.Y. Li, H. Tian, C.H. Huang, A new carbazole-
based phenanthrenyl ruthenium complex as sensitizer for a dye-sensitized
solar cell, Inorg. Chim. Acta 361 (2008) 2835–2840.
[50] S.H. Fan, K.Z. Wang, W.C. Yang, A carbazole-containing difunctional RuII com-
plex that functions as a pH-induced emission switch and an efficient sensitizer
for solar cells, Eur. J. Inorg. Chem. (2009) 508–518.
[36] S. Encinas, K.L. Bushell, S.M. Couchman, J.C. Jeffrey, M.D. Ward, L. Flamigni, F.
Barigelletti, J. Chem. Soc., Dalton Trans. (2000) 1783–1792.