Tuning photophysical and electrochemical properties of cationic iridium(III) complex salts with imidazolyl substituents by proton and anions

Article abstract of DOI:10.1021/om700623j

A series of cationic iridium(III) complex salts, 1-5, were synthesized containing different phenanthroline derivatives. Their photophysical and electrochemical properties were investigated. The influences of anions and proton on the photophysical and electrochemical properties were also studied in detail. Upon addition of CF₃COOH, the emission wavelength was significantly red-shifted and the emission color changed from yellow to red. In addition, the addition of F^-, CH₃COO^-, and H₂PO₄^- can also cause significant variations in UV-vis absorption and emission spectra. Upon addition of F^-, CH ₃COO^-, and H₂PO₄^-, the solution colors of 1-3 changed from yellow-green to brown and the emission of 1-3 was quenched completely, which can be observed by the naked eye.

Full text of DOI:10.1021/om700623j

5922
Organometallics 2007, 26, 5922-5930
Tuning Photophysical and Electrochemical Properties of Cationic
Iridium(III) Complex Salts with Imidazolyl Substituents by Proton
and Anions
Qiang Zhao,† Shujuan Liu,‡ Mei Shi,† Fuyou Li,*,† Hao Jing,† Tao Yi,† and
Chunhui Huang*,†
Department of Chemistry and Laboratory of AdVanced Materials, Fudan UniVersity, Shanghai, 200433,
People’s Republic of China, and Institute of AdVanced Materials (IAM), Nanjing UniVersity of Posts and
Telecommunications, 66 XinMoFan Road, Nanjing 210003, People’s Republic of China
ReceiVed June 22, 2007
A series of cationic iridium(III) complex salts, 1-5, were synthesized containing different phenanthroline
derivatives. Their photophysical and electrochemical properties were investigated. The influences of anions
and proton on the photophysical and electrochemical properties were also studied in detail. Upon addition
of CF3COOH, the emission wavelength was significantly red-shifted and the emission color changed
-
from yellow to red. In addition, the addition of F-, CH3COO-, and H2PO4 can also cause significant
-
variations in UV-vis absorption and emission spectra. Upon addition of F-, CH3COO-, and H2PO4 ,
the solution colors of 1-3 changed from yellow-green to brown and the emission of 1-3 was quenched
completely, which can be observed by the naked eye.
oxygen concentration,8 and metal ions.5c However, as the best
phosphorescent dyes,9 the applications of iridium(III) complexes
in chemosensors were mainly limited to recognizing oxygen10
and the Hg2+ cation.11
Introduction
Phosphorescent heavy-metal complexes have been explored
for a multitude of photonic applications including organic light-
emitting diodes,1 photovoltaic cells,2 biological labeling re-
agents,3 and hydrogen production via photoreduction of water.4
Recently, phosphorescent heavy-metal complexes have also
attracted considerable interest as sensors,5 because of their
significant Stokes shifts for easy separation of excitation and
emission and relatively long lifetimes compared with purely
organic luminophores.6 Many phosphorescent heavy-metal
complexes, such as platinum(II), rhenium(I), and ruthenium-
(II) complexes, have been explored as chemosensors for anions,7
On the other hand, anion recognition and sensing have been
of most interest in recent years because of their important roles
in biological processes and environmental assays.12 Various
types of pure organic dyes have been used as receptors for
anionic species.12,13 Up to now, only one example of iridium-
(III) complex salts has been reported to recognize chloride
anions with low sensitivity (Ksv-1 ) 34 mmol L-1).14
In our previous report, the imidazolyl group of imidazo[4,5-
f][1,10]phenanthroline can interact with a proton, and the
NH group can also be deprotonated by addition of a strong
alkali.15 Sensitivity to proton and alkali might be expected for
iridium(III) complexes incorporating an imidazo[4,5-f][1,10]-
phenanthroline unit. Herein, three cationic iridium(III) complex
* To whom correspondence should be addressed. Fax: 86-21-55664621.
Tel: 86-21-55664185. E-mail: fyli@fudan.edu.cn (F.Y.L.); chhuang@
pku.edu.cn (C.H.H.).
† Fudan University.
‡ Nanjing University of Posts and Telecommunications.
(1) (a) Tsuboyama, A.; Iwawaki, H.; Fururori, M.; Mukaide, T.;
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salts [Ir(ppy)2(N∧N)]+PF6 (1-3) (see Chart 1) based on
-
different phenanthroline derivatives (N∧N ligands) were syn-
thesized, and the tuning of the photophysical and electrochemical
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10.1021/om700623j CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/24/2007

Cationic Iridium(III) Complex Salts
Organometallics, Vol. 26, No. 24, 2007 5923
Chart 1. Chemical Structures of the Complex Salts 1-5
further purification. 2-Phenylpyridine and N-ethyl-3-carbazolecar-
boxaldehyde were obtained from Acros and used without further
purification.
Synthesis of the Phenanthroline Derivatives. The phenanthro-
line derivatives were synthesized according to a previous report.16
Synthesis of the Iridium(III) Complex Salts. All iridium(III)
-
complex salts [Ir(ppy)2(N∧N)]+PF6 were prepared by the same
procedure. Herein, only the synthesis of complex salt [Ir(ppy)2-
-
(phen)]+PF6 (1) is described in detail.
Complex Salt 1. The cyclometalated iridium(III) chlorobridged
dimer [Ir(ppy)2Cl]2 was prepared according to literature methods.17
A solution of [Ir(ppy)2Cl]2 (0.079 mmol) and 2-phenylimidazo-
[4,5-f][1,10]phenanthroline (0.158 mmol) in CH2Cl2-MeOH
(30 mL, 2:1 v/v) was heated to reflux. After 4 h, the yellow solution
was cooled to room temperature, and then a 10-fold excess of
potassium hexafluorophosphate was added. The suspension was
stirred for 2 h and then was filtered to remove insoluble inorganic
salts. The solution was evaporated to dryness under reduced
pressure. The crude product was applied to a silica gel column and
eluted with CH2Cl2-acetone (15:1) to afford a yellow solid in 63%
yield. 1H NMR (400 MHz, d6-DMSO), δ(ppm): 9.15 (d, 2H, J )
8.0), 8.26 (t, 4H, J ) 8.0), 8.15 (d, 2H, J ) 4.0), 8.03-8.07 (m,
2H), 7.95 (d, 2H, J ) 7.6), 7.86 (t, 2H, J ) 7.6), 7.63 (t, 2H, J )
7.2), 7.56 (t, 1H, J ) 7.2), 7.51 (d, 2H, J ) 5.6), 7.05 (d, 2H, J )
7.2), 6.92-6.99 (m, 4H), 6.30 (d, 2H, J ) 7.2). 13C NMR
(100 MHz, d6-DMSO), δ(ppm): 167.5, 153.4, 151.0, 149.8, 149.1,
144.8, 144.7, 139.3, 132.9, 131.9, 130.9, 129.9, 127.7, 127.2, 125.7,
124.5, 123.1, 120.6. Anal. Calcd for IrC41H28N6F6P: C, 52.28; H,
3.00; N, 8.92. Found: C, 52.42; H, 3.32; N, 8.67. MS(LDI-TOF):
m/e 797.3 (M - PF6).
properties of 1-3 by anions and proton was investigated. For
comparison, two other cationic iridium(III) complex salts,
[Ir(ppy)2(L2)]+PF6 (4) and [Ir(ppy)2(L3)]+PF6 (5), without
the N-H group were also studied.
-
-
Experimental Section
Complex Salt 2. Yield: 57%. 1H NMR (400 MHz, d6-DMSO),
δ(ppm): 9.25 (d, 2H), 8.16-8.26 (m, 6H), 8.06-8.09 (m, 2H),
7.95 (d, 2H), 7.86 (t, 2H), 7.51 (d, 2H), 7.43 (t, 1H), 7.03-7.13
(m, 4H), 6.93-6.99 (m, 4H), 6.29 (d, 2H). 13C NMR (100 MHz,
d6-DMSO), δ(ppm): 167.5, 157.8, 153.1, 150.9, 149.8, 149.3,
144.9, 139.4, 138.6, 133.2, 132.8, 131.9, 130.9, 127.8, 127.6, 125.7,
124.5, 123.1, 120.6, 120.2, 118.0, 113.7, 56.7, 19.2. Anal. Calcd
for IrC41H28N6F6PO: C, 51.41; H, 2.95; N, 8.77. Found: C, 51.21;
H, 2.66; N, 8.43. MS(LDI-TOF): m/e 813.3 (M - PF6).
Complex Salt 3. Yield: 55%. 1H NMR (400 MHz, d6-DMSO),
δ(ppm): 9.21 (d, 2H, J ) 8.4), 9.05 (s, 1H), 8.41 (d, 1H, J ) 8.4),
8.27 (t, 3H, J ) 6.8), 8.05-8.17 (m, 4H), 7.96 (d, 2H, J ) 7.6),
7.87 (t, 3H, J ) 8.4), 7.70 (d, 1H, J ) 8.4), 7.53 (m, 3H), 7.30 (t,
1H, J ) 7.6), 6.93-7.07 (m, 6H), 6.30 (d, 2H, J ) 7.6), 4.50-
4.55 (m, 2H), 1.37 (t, 3H, J ) 7.2). 13C NMR (100 MHz,
d6-DMSO), δ(ppm): 167.7, 154.7, 151.0, 149.5, 148.8, 144.6,
144.4, 141.3, 140.8, 139.2, 132.8, 131.9, 130.8, 127.3, 127.0, 125.6,
124.3, 123.2, 122.8, 121.0, 120.8, 120.6, 120.2, 119.5, 38.0, 14.4.
Anal. Calcd for IrC49H35N7F6P: C, 55.57; H, 3.33; N, 9.26.
Found: C, 55.76; H, 3.55; N, 9.40. MS(LDI-TOF): m/e 914.3 (M
- PF6).
General Experiments. Commercially available chemical re-
agents were used without further purification. NMR spectra were
taken on a Mercury Plus 400 MHz NMR spectrometer. Elemental
analyses were performed on a VarioEL III O-Element analyzer
system. Mass spectra were obtained on a Shimadzu matrix-assisted
laser desorption/ionization time-of-flight mass spectrometer (MALDI-
TOF-MASS). UV-visible absorption spectra were recorded using
a Shimadzu 3000 UV-vis-NIR spectrophotometer. Photolumi-
nescence spectra were measured on an Edinburgh LFS920 fluo-
rescence spectrophotometer. Luminescence quantum yields of the
iridium complex salts in solution were measured with reference to
quinine sulfate (ΦF ) 0.56 in 1 mol L-1 sulfuric acid). The solutions
were degassed by three freeze-pump-thaw cycles. Photolumi-
nescent lifetime was recorded on a single photon counting
spectrometer from Edinburgh Instruments (FLS920) with a hydrogen-
filled pulse lamp as the excitation source. The data were analyzed
by iterative convolution of the luminescence decay profile with the
instrument response function using the software package provided
by Edinburgh Instruments.
Materials. IrCl3‚3H2O, phenanthroline, benzaldehyde, and 2-hy-
droxybenzaldehyde were industrial products and used without
Complex Salt 4. Yield: 65%. 1H NMR (400 MHz, d6-DMSO),
δ(ppm): 8.91 (d, 2H, J ) 8.0), 8.39 (s, 2H), 8.27 (d, 2H, J ) 8.0),
8.20 (d, 2H, J ) 5.2), 8.04-8.07 (m, 2H), 7.96 (d, 2H, J ) 8.0),
7.88 (t, 2H, J ) 7.6), 7.47 (d, 2H, J ) 6.0), 7.07 (t, 2H, J ) 7.2),
6.90-7.01 (m, 4H), 6.30 (d, 2H, J ) 7.6). 13C NMR (100 MHz,
d6-DMSO), δ(ppm): 167.5, 151.3, 150.5, 149.8, 146.7, 144.7,
139.5, 139.4, 131.9, 131.8, 130.9, 129.0, 127.8, 125.7, 124.5, 123.1,
120.6. Anal. Calcd for IrC34H24N4F6P: C, 49.45; H, 2.93; N, 6.78.
Found: C, 49.23; H, 2.72; N, 6.45. MS(LDI-TOF): m/e 681.2 (M
- PF6).
(13) For recent examples: (a) Bondy, C. R.; Gale, P. A.; Loeb, S. J. J.
Am. Chem. Soc. 2004, 126, 5030-5031. (b) Chmielewski, M. J.; Charon,
M.; Jurczak, J. Org. Lett. 2004, 6, 3501-3504. (c) Nielsen, K. A.; Jeppesen,
J. O.; Levillain, E.; Becher, J. Angew. Chem., Int. Ed. 2003, 42, 187-191.
(d) Wallace, K. J.; Belcher, W. J.; Syed, K. F.; Seed, J. W. J. Am. Chem.
Soc. 2003, 125, 9699-9715. (e) Best, M. D.; Tobey, S. L.; Anslyn, E. V.
Coord. Chem. ReV. 2003, 240, 3-15. (f) Choi, K.; Hamilton, A. D. Coord.
Chem. ReV. 2003, 240, 101-110. (g) Mizuno, T.; Wei, W.-H.; Eller, L.
R.; Sessler, J. L. J. Am. Chem. Soc. 2002, 124, 1134-1135. (h) Haj-Zaroubi,
M.; Mitzel, N. W.; Schmidtchen, F. P. Angew. Chem., Int. Ed. 2002, 41,
104-107. (i) Liu, Z. Q.; Shi, M.; Li, F. Y.; Fang, Q.; Chen, Z. H.; Yi, T.;
Huang, C. H. Org. Lett. 2005, 7, 5481-5484. (j) Zhou, Z. G.; Xiao, S. Z.;
Xu, J.; Liu, Z. Q.; Shi, M.; Li, F. Y.; Yi, T.; Huang, C. H. Org. Lett. 2006,
8, 3911-3914. (k) Zhou, Z. G.; Yang, H.; Shi, M.; Xiao, S. Z.; Li, F. Y.;
Yi, T.; Huang, C. H. ChemPhysChem 2007, 8, 1289-1292.
Complex Salt 5. Yield: 50%. 1H NMR (400 MHz, CDCl3), δ-
(ppm): 9.30 (d, 1H, J ) 8.4), 9.14 (d, 1H, J ) 8.4), 8.24 (t, 2H,
J ) 4.8), 8.02-8.05 (m, 1H), 7.89-7.96 (m, 2H), 7.68-7.79 (m,
(14) Goodall, W.; Williams, J. A. G. J. Chem. Soc., Dalton Trans. 2000,
2893-2896.
(16) Han, M. J.; Gao, L. H.; Wang, K. Z. New J. Chem. 2006, 30, 208-
214.
(17) Nonoyama, K. Bull. Chem. Soc. Jpn. 1974, 47, 467-468.
(15) Xiao, S. Z.; Tao Yi, T.; Zhou, Y. F.; Zhao, Q.; Li, F. Y.; Huang, C.
H. Tetrahedron 2006, 62, 10072-10078.

5924 Organometallics, Vol. 26, No. 24, 2007
Zhao et al.
Table 1. Crystallographic Data for 1
emipirical formula C43H30IrN6Cl4PF6
7H), 7.58-7.61 (m, 3H), 7.45 (d, 1H, J ) 5.6), 7.34 (d, 1H, J )
5.6), 7.07-7.11 (m, 2H), 6.95-7.01 (m, 3H), 6.82 (t, 1H, J ) 7.2),
6.39-6.42 (m, 2H), 4.75-4.88 (m, 2H), 1.65 (t, 3H, J ) 7.2). 13
C
cryst syst
space group
cryst size, mm
a, Å
b, Å
c, Å
monoclinc
P21/c
NMR (100 MHz, d6-DMSO), δ(ppm): 167.5, 155.6, 151.5, 150.9,
149.8, 149.7, 148.8, 145.1, 144.8, 144.7, 144.6, 139.4, 137.1, 132.9,
132.6, 131.9, 131.0, 130.9, 130.4, 130.1, 129.7, 128.2, 127.7, 126.8,
126.4, 125.7, 124.6, 124.5, 123.0, 122.9, 120.7, 29.7, 16.2. Anal.
Calcd for IrC43H32N6F6P: C, 53.39; H, 3.34; N, 8.69. Found: C,
53.61; H, 3.15; N, 8.97. MS(LDI-TOF): m/e 825.3 (M - PF6).
Theoretical Calculations. The calculations were performed
using the Gaussian 03 suite of programs.18 The starting geometry
was from the single-crystal structure of complex salt 1. DFT
calculations (full geometry optimization) were carried out by
B3LYP. The LANL2DZ basis set was used to treat the iridium
atom, whereas the 3-21G* basis set was used to treat all other atoms.
The contours of the HOMO and LUMO orbitals were plotted.
Electrochemical Measurements. Electrochemical measurements
were carried out in a one-compartment cell under an N2 atmosphere,
equipped with a glassy-carbon working electrode, a platinum wire
counter electrode, and an Ag/Ag+ reference electrode with an Eco
Chemie Autolab. Measurements of oxidation and reduction were
undertaken in the anhydrous solution of CH2Cl2 and THF,
respectively, containing the supported electrolyte of 0.10 mol L-1
tetrabutylammonium hexafluorophosphate (Bu4N+‚PF6-). The scan
0.10 × 0.10 × 0.08
14.079(3)
12.862(3)
23.706(5)
90
93.05(3)
90
4286.7(15)
4
R, deg
â, deg
γ, deg
V, Å3
Z
calcd density, g cm-3
µ, mm-1
1.719
3.468
2176
F(000)
final R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
R1 (all data)
wR2 (all data)
GOF on F2
0.0396
0.0783
0.0779
0.0901
0.964
were synthesized by the bridge-splitting reactions of [Ir-
(ppy)2Cl]2 and consequently coordinated with the corresponding
phenanthroline derivatives. Compared with the synthesis of
neutral iridium(III) complex containing â-diketone ligands,
which needs harsh reaction conditions (reflux in a high-boiling
solvent mixture) and much longer reaction time, the synthesis
of cationic iridium complex salts [Ir(ppy)2(N∧N)]+PF6- can be
carried out under mild reaction conditions. In our case, new
iridium(III) complex salts were obtained with lower decomposi-
tion, limited workup, and good yields. These complex salts were
characterized by 1H NMR, 13C NMR, MALDI-TOF, and
elemental analysis. However, the imidazolyl N-H signal in the
N∧N ligand of 1 could not be detected in d6-DMSO solution
rate was 50 mV s-1
.
X-ray Crystallography Analysis. The single crystal of the
complex salt 1 was mounted on a glass fiber and transferred to a
Bruker SMART CCD area detector. Crystallographic measurement
was carried out using a Bruker SMART CCD diffractometer, σ
scans, and graphite-monochromated Mo KR radiation (λ ) 0.71073
Å) at room temperature. The structure was solved by direct methods
and refined by full-matrix least-squares on F2 values using the
program SHELXS-97.19 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were calculated in ideal geom-
etries. For the full-matrix least-squares refinements [I > 2σ(I)], the
unweighted and weighted agreement factors of R1 ) ∑(Fo - Fc)/
∑Fo and wR2 ) [∑w(Fo2 - Fc2)2/∑wFo4]1/2 were used. The crystal
data and details of the structure determinations are summarized in
Table 1. CCDC reference number for 1 is 628443.
1
from the H NMR spectra.
Crystal Structure of 1. A single crystal of 1 was obtained
from a mixed solution of CH2Cl2 and hexane. The ORTEP
diagram of 1 is depicted in Figure 1. It can be seen that the
iridium(III) center in 1 adopts a distorted octahedral coordination
geometry. Selected relevant bond parameters of 1 and the
previously reported iridium(III) complex [Ir(ppy)2(di-C9H19-
bpy)]+PF6- 11a are listed in Table 2. All bond lengths and bond
angles of 1 are within normal ranges.11a The metalated C atoms
of the ppy ligands are in a mutually cis arrangement. The strong
trans influence of the phenyl groups results in slightly longer
Ir-N (N∧N ligands) bond lengths than the distances of Ir-N
(C∧N ligands).20 Similar to other related complex salts, the
cation [Ir(ppy)2(N∧N)]+ is connected to the anion PF6- by weak
intra- and intermolecular C-H---F-P hydrogen bonds with an
average H---F distance of 2.56 Å and intramolecular N-H---
F-P hydrogen bonds with an average H---F distance of 2.14
Å.
Results and Discussion
Synthesis. The phenanthroline derivative ligands were syn-
thesized according to previous reports.16 Due to poor solubility
in most organic solvents, all phenanthroline derivative ligands
were not purified and were used directly to synthesize the
iridium(III) complex salts. The synthetic procedure for the
cationic iridium(III) complex salts contains two steps. The
dinuclear cyclometalated iridium(III) chlorobridged precursor
[Ir(ppy)2Cl]2 was synthesized by the same method as reported
by Nonoyama.17 Then the cationic iridium(III) complex salts
In addition, the molecular packing structure of 1 is shown in
Figure 2. A significant degree of π-π overlap with an
interplanar separation of approximately 3.35 Å could be
observed between the adjacent N∧N ligands of 1, which implies
the existence of strong ligand (N∧N)-ligand (N∧N) (π-π)
interactions.
Absorption Spectroscopy. The UV-vis absorption spectra
of all complex salts are shown in Figure 3, and the electronic
absorption data are listed in Table 3. For complex salts 1, 2, 4,
and 5, intense absorption bands below 370 nm could be observed
and are assigned to spin-allowed intraligand IL (πfπ*) (ppy
and phenanthroline derivatives) transitions. Moderately intense
absorption bands in the range 370-440 nm and weak absorption
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A.
G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, reVision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
(19) Sheldrick, G. M. SHELXTL-Plus V5.1 Software Reference Manual;
Bruker AXS Inc.: Madison, WI, 1997.
(20) Coe, B. J.; Glenwright, S. J. Coord. Chem. ReV. 2000, 203, 5-80.

Cationic Iridium(III) Complex Salts
Organometallics, Vol. 26, No. 24, 2007 5925
Figure 1. ORTEP diagram of 1 with the thermal ellipsoids drawn at the 30% probability level and the H atoms removed for clarity.
Figure 3. Absorption spectra of 1-5 in CH2Cl2 solution at a
concentration of 1 × 10-5 mol L-1 at 298 K.
Table 3. Absorption Data of 1-5 in CH2Cl2 at 298 K
complex salt
λabs(log ꢀ)/[nm]
1
2
3
4
5
279(4.84), 299(4.69), 348(4.18), 390(3.93), 416(3.85)
273(4.89), 296(4.71), 334(4.53), 393(4.07), 416(4.00)
286(4.89), 342(4.65), 379(4.41), 420(3.98)
266(4.78), 333(4.05), 383(3.90), 416(3.57)
267(4.92), 298(4.70), 341(4.20), 387(4.04), 410(3.98)
Figure 2. Molecular packing of 2 with the H atoms removed for
clarity.
Table 2. Selected Bond Parameters (Å, deg) of 1
1
[Ir(ppy)2(di-C9H19-bpy)]+PF6
- 11a
spin-forbidden 3MLCT (dπ(Ir)fπ*(phenanthroline derivatives))
transitions. For complex salt 3, its 1MLCT and 3MLCT
transitions are shifted to 400-460 nm and above 460 nm,
respectively. The red shift and higher extinction coefficients
(ꢀ) of MLCT and MLCT transitions were observed when
compared with those of other complex salts and ascribed to the
presence of a carbazole fragment.
Ir-C (Å)
2.009(5)
2.017(5)
2.037(4)
2.042(4)
2.139(4)
2.144(4)
88.55(19)
80.47(19)
80.7(2)
92.19(19)
93.34(19)
97.43(17)
97.21(17)
173.35(16)
172.76(18)
2.015(7)
Ir-N(CN) (Å)
Ir-N(NN) (Å)
2.057(6)
2.151(6)
94.5(4)
1
3
C-Ir-C (deg)
C-Ir-N(CN) (deg)
80.1(3)
94.9(3)
Luminescence Spectroscopy. The room-temperature pho-
toluminescence spectra of all complex salts in CH2Cl2 solution
and solid film are shown in the Supporting Information, and
corresponding photoluminescence data of complex salts are
summarized in Table 4. Figure 4 shows the photoluminescence
spectra of complex salt 1 (as an example) in different conditions.
It can be seen that all complex salts emit intense luminescence
with similar emission wavelengths in the range 568-583 nm
in CH2Cl2 solution at room temperature. The observed emission
lifetimes in the microsecond and sub-microsecond time scales
(Table 4) indicate the phosphorescent nature of the emissions.
In addition, photoluminescence spectra of these complex salts
in solid film were also measured and are similar to those in
CH2Cl2 solution.
C-Ir-N(NN) (deg)
170.3(3)
172.7(4)
N(CN)-Ir-N(CN) (deg) 170.76(17)
N(CN)-Ir-N(NN) (deg) 96.32(16)
90.51(16)
89.9(2)
95.9(2)
93.10(15)
94.49(17)
N(NN)-Ir-N(NN) (deg) 77.07(15)
76.3(3)
bands above 440 nm were also observed, which are assigned
to spin-allowed metal-to-ligand charge-transfer MLCT (dπ-
(Ir)fπ*(phenanthroline derivatives and ppy)) transitions and
1

5926 Organometallics, Vol. 26, No. 24, 2007
Zhao et al.
Table 5. Electrochemical Data for 1-5
1
2
3
4
5
Eox/V
Ere/V
1.03
-1.98
1.05
-2.01
0.84, 1.10
-2.01
1.03
-1.98
1.05
-2.01
Supporting Information), and the data are listed in Table 5. An
irreversible oxidation wave was observed at similar potentials
between 1.03 and 1.10 V for all complex salts. It is assumed
that pure metal-centered oxidation is reversible and irreversibility
increases as the contribution to the HOMO of the cyclometa-
lating phenyl(s) increases.22 Therefore, the irreversible oxidation
process is assigned to orbits receiving a strong contribution from
the iridium center and Ir-C- σ-bond orbits at the same time.
Interestingly, an additional irreversible oxidation wave at 0.84
V was also observed for complex salt 3. According to the
previous report,23 we assign it to the oxidation of carbazole. In
addition, all complex salts exhibit a similar irreversible reduction
wave at approximately -2.00 V. This reduction wave of 1-5
can be assigned to the reduction of the phenanthroline derivative
ligands.
Theoretical Calculations. To further investigate the nature
of the excited state, density functional theory (DFT) for 1 and
4 was performed. The two complex salts have similar HOMO
and LUMO distributions (Table 6). The HOMO distributions
primarily reside on the iridium center and cyclometalated
ligands. For 4, the LUMO distribution is localized on the whole
phenanthroline ligand (N∧N ligand). Similarly, the LUMO
distribution of 1 is only localized on the phenanthroline
fragment. The imidazolyl group and the substituent phenyl group
do not participate in the LUMO distribution. The calculated
HOMO, LUMO, and energy of the triplet excited state (ET) are
listed in Table 6. The complex salts 1 and 4 show similar ET
values, which is in agreement with their similar electrochemical
properties and emission wavelengths. Therefore, similar excited
states and photophysical properties were observed for 1-5 with
different imidazolyl groups and substituents on the imidazole.
Tuning Photophysical and Electrochemical Properties of
1-3 upon Addition of Anions. The complexation abilities of
1-3 with anions were investigated by UV-vis absorption
titration experiments (Figure 5 and Supporting Information). For
example, upon addition of F-, the absorption bands of 1 at 277
and 404 nm gradually decrease and three new bands centered
at 300, 338, and 476 nm start to develop with three distinct
isosbestic points at 287, 385, and 415 nm (Figure 5), indicating
strong ground state interactions between 1 and the fluoride
anion, and a dramatic color change from weak yellow-green to
brown can be observed with the naked eye (Figure 6). Similar
phenomena were observed for complex salts 2 and 3 upon
addition of the fluoride anion (Figure 5).
Figure 4. Photoluminescent spectra of 1 in different conditions.
λex ) 315 nm.
Table 4. Photoluminescent Data of 1-5
complex salt
medium (T [K])
λ
PL,max (nm)
Φem
τ (ns)
1
CH2Cl2 (298)
CH3CN (298)
solid film (298)
glass (77)
CH2Cl2 (298)
CH3CN (298)
solid film (298)
glass (77)
CH2Cl2 (298)
CH3CN
solid film (298)
glass (77)
CH2Cl2 (298)
CH3CN (298)
solid film (298)
glass (77)
CH2Cl2 (298)
CH3CN (298)
solid film (298)
glass (77)
568
587
568
528
583
593
584
528
570
580
577
529
571
583
568
515
572
582
580
524
0.24
704.3
2
3
4
5
0.22
0.19
0.25
0.22
469.0
592.5
235.4
538.2
We also studied the low-temperature photoluminescence
spectra of all complex salts in CH2Cl2 (Supporting Information).
A blue shift of emission maxima was observed for all complex
salts from fluid solution at room temperature to rigid matrix at
77 K, which was often observed for MLCT and LLCT emitters
based on cyclometalated iridium(III) diimine complexes.11 For
typical MLCT emitters, such as the well-known [Ru(bpy)3]2+
complex and analogous compounds, such a blue shift is usually
in the range 1000-2000 cm-1, and it is also in the same range
for Ir(III) cyclometalated compounds, which are reported to be
pure MLCT emitters.11c Hence, for 1-5, such slight blue shifts
of <2000 cm-1 imply that the emissions of 1-5 are mainly
assigned to MLCT transitions. The blue shift is caused by fast
solvent reorganization in fluid solution at room temperature,
which can stabilize the CT states before the emission takes place.
However, at 77 K, this stabilization of CT states is hampered
and the blue shift of emission maxima occurs.11,21
In addition, the photoluminescence spectra of all complex
salts in different solvents were also investigated (see Supporting
Information), and the data are summarized in Table 4. The
emission maxima for all complex salts occur at higher energy
in less polar CH2Cl2 than those in more polar CH3CN, which
is also very common for cyclometalated iridium(III) diimine
MLCT emitters.11
The emission spectra titration of 1-3 with anions was also
measured. It can be seen from Figure 7 that the emission of the
three complex salts is quenched upon addition of F-. Moreover,
similar changes in absorption and emission spectra of complex
-
salts 1-3 were also observed when CH3COO- and H2PO4
were added (Supporting Information), which implied strong
interaction between the complex salts 1-3 and these anions.
However, no obvious spectral variations were measured for 1-3
-
upon addition of other anions (such as Cl-, Br-, I-, NO3
,
ClO4-, and CF3COO-). The binding constant values (K) for
the three complex salts 1-3 calculated from fluorescence
Electrochemical Properties. The electrochemical properties
of the complex salts were studied by cyclic voltammetry (see
(22) Calogero, G.; Giuffrida, G.; Serroni, S.; Ricevuto, V.; Campagna,
S. Inorg. Chem. 1995; 34, 541-545.
(23) Stahl, R.; Lambert, C.; Kaiser, C.; Wortmann, R.; Jakober, R.
Chem.-Eur. J. 2006, 12, 2358-2370.
(21) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.;
von Zelewsky, A. Coord. Chem. ReV. 1988, 84, 85-277.

Cationic Iridium(III) Complex Salts
Organometallics, Vol. 26, No. 24, 2007 5927
Figure 5. Changes in the UV-vis absorption spectra of 1-3 (20 µM) in CH3CN solution with various amounts of F-.
Table 6. HOMO and LUMO Distributions of 1, 4, and 1+H+
a Calculated energy levels of triplet excited state.
titration data are summarized in Table 7. We can see that the
three complex salts 1-3 prefer to bind F- and CH3COO- over
H2PO4-. Especially, the binding constant values (K) of 1 for
F-, CH3COO-, and H2PO4- were 7.01 × 104, 1.42 × 104, and
3.03 × 103 M-1, respectively (Table 7). So, 1 can be used as a
selective chemosensor for F-.
change in UV-vis absorption and emission spectra could be
observed for 5 upon addition of F- (Supporting Information).
Hence, we can conclude that the interaction of NH in the
imidazolyl group of the N∧N ligand with anions is responsible
for the significant optical variations. Unfortunately, we cannot
1
demonstrate from the H NMR titration experiments that the
To understand the optical response mechanism of 1-3 for
interaction of NH with anions is the formation of a hydrogen
bond or deprotonation since the imidazolyl N-H signal could
anions, the response of 5 to F- was also measured. No obvious

5928 Organometallics, Vol. 26, No. 24, 2007
Zhao et al.
Table 7. Binding Constants (K) of Complex Salts 1-3 for
F-, CH3COO-, and H2PO4 (M-1) Determined from
-
Fluorescence Titration Spectra
anion
1
2
3
F-
7.01 × 104
1.42 × 104
3.03 × 103
9.62 × 104
3.33 × 104
7.31 × 102
3.86 × 104
3.11 × 104
5.78 × 103
CH3COO-
-
H2PO4
To better understand the optical response mechanism of 1-3
for anions, we measured the optical response of 1 to the weak
organic base NEt3 and strong bases Bu4NOH (Figure 8). When
strong bases such as Bu4NOH were added into the solution of
1, obvious spectral variations of the absorption and emission
bands of 1 were observed, which are similar to those of 1 after
addition of fluoride anion. In contrast, no obvious changes were
observed upon addition of weak organic base NEt3. This further
confirms the suspicion that the reaction between the NH bond
of the imidazolyl group of 1-3 and F- is a deprotonation
process and not a hydrogen-bonding effect.25
Figure 6. Color and emission color variations observed in
acetonitrile solutions of 1 (5 × 10-4 M) in the presence of 2 equiv
of F- and CF3COOH.
Furthermore, we also investigated the influence of fluoride
anions on the electrochemical properties of 1-3. After the
addition of fluoride anions, no evident change was observed
for the reduction wave (Figure 9 and Supporting Information),
indicating that the interaction of anions with imidazole N-H
does not change the LUMO energy level and distribution
significantly. However, the addition of fluoride anions causes
obvious variation of the oxidation wave (Figure 9 and Support-
not be detected in d6-DMSO solution from the 1H NMR spectra.
Recently, many anion sensors containing recognition moieties
such as amide, urea, and thiourea with acidic protons have been
reported to undergo anion-induced deprotonation.24 In addition,
the intramolecular N-HsF-P hydrogen bonds existing in these
complex salts can also enhance the acidity of N-H, increasing
the deprotonation trend.
Figure 7. Changes in the luminescence spectra of 1-3 (20 µM) in air-equilibrated CH3CN solution with various amounts of F- (λex ) 360
nm). Inset: fluorimetric titration.

Cationic Iridium(III) Complex Salts
Organometallics, Vol. 26, No. 24, 2007 5929
Figure 8. Response of UV-vis absorption spectra and lumines-
cence spectra of 1 to Et3N and Bu4NOH.
Figure 9. Cyclic voltammograms of 1 before and after addition
of F- and CF3COOH.
Figure 10. Absorption and photoluminescence spectra of 1 (20
µM) in CH3CN solution before and after addition of CF3COOH.
ing Information). Upon addition of fluoride anions, the oxidation
potential attributed to the iridium center and Ir-C- σ-bond
orbits was shifted positively, and a new irreversible oxidation
wave appeared at more negative potential. The irreversible
oxidation wave at 0.67 V could be assigned to the oxidation of
the imidazolyl group after deprotonation.
The mechanism of fluorescence quenching in the presence
of F-, CH3COO-, and H2PO4- is somewhat ambiguous. Perhaps
the deprotonation process results in a greater degree of distortion
between its excited and ground state surfaces and increases the
probability of radiationless transitions. In addition, there is also
a probability of a photoinduced electron transfer (PET) process
from the lone electron pair on the imidazolyl group after
deprotonation, which quenches the emission of complex salts.
Tuning Photophysical and Electrochemical Properties of
1-3 upon Addition of CF3COOH. Considering the imidazolyl
group in the N∧N ligands, sensitivity to protons might be
expected for 1-3. Herein, because of very weak interaction of
1-3 with the anion CF3COO-, CF3COOH was chosen as a
source of protons. Significant changes in UV-vis absorption
and emission spectra were observed when CF3COOH was added
into the CH3CN solutions of 1-3 (Figure 10 and Supporting
Information). For example, Figure 10 gives the variations of
photophysical properties of 1 upon addition of CF3COOH. In
particular, upon addition of CF3COOH, the emission wavelength
of 1 was red-shifted and the emission color changed from yellow
to red (Figure 6). Similar phenomena were observed for complex
salts 2 and 3 upon addition of CF3COOH (Supporting Informa-
tion).
Because the addition of CF3COO- cannot induce the optical
variations of the three complex salts 1-3 (Supporting Informa-
tion), the evident changes in UV-vis absorption and emission
spectra of 1-3 after the addition of CF3COOH should be
attributed to the interaction of a proton with 1-3. To further
understand this point, theoretical calculations on the adduct 1
+ H+ were performed, and the HOMO and LUMO distributions
are shown in Table 6. Compared with 1, no variation was
observed for the HOMO distribution of 1+H+. However, there
is a significant difference in LUMO distribution. The LUMO
distribution of 1+H+ resides on the whole N∧N ligand, whereas
the LUMO distribution of 1 is localized only on the phenan-
throline fragment of the N∧N ligand (Table 6). In addition, the
calculated energy levels of the HOMO and LUMO and the
energy of the triplet excited state (ET) for 1+H+ decrease
markedly in comparison with those of 1 (Table 6), which is
consistent with the obvious red shift of emission wavelength.
So, protonation causes the imidazolyl and phenyl units to
become involved in the LUMO, increasing the overall degree
of delocalization and hence causing a large calculated stabiliza-
(24) (a) Cho, E. J.; Moon, J. W.; Ko, S. W.; Lee, J. Y.; Kim, S. K.;
Yoon, J.; Nam, K. C. J. Am. Chem. Soc. 2003, 125, 12376-12377. (b)
Gunnlaugsson, T.; Kruger, P. E.; Jensen, P.; Pfeffer, F. M.; Hussey, G. M.
Tetrahedron Lett. 2003, 44, 8909-8913. (c) Lee, J. Y.; Cho, E. J.; Mukamel,
S.; Nam, K. C. J. Org. Chem. 2004, 69, 943-950. (d) Va´zquez, M.;
Fabbrizzi, L.; Taglietti, A.; Pedrido, R. M.; Gonza´lez-Noya, A. M.; Bermejo,
M. R. Angew. Chem. 2004, 116, 1996-1999; Angew. Chem., Int. Ed. 2004,
43, 1962-1965. (e) Boiocchi, M.; Boca, L. D.; Esteban-Go´mez, D.;
Fabbrizzi, L.; Licchelli, M.; Monzani, E. J. Am. Chem. Soc. 2004, 126,
16507-16514. (f) Amendola, V.; Boiocchi, M.; Fabbrizzi, L.; Palchetti,
A. Chem.-Eur. J. 2005, 11, 120-127. (g) Boiocchi, M.; Boca, L. D.;
Esteban-Go´mez, D.; Fabbrizzi, L.; Licchelli, M.; Monzani, E. Chem.-Eur.
J. 2005, 11, 3097-3104. (h) Gomez, D. E.; Fabbrizzi, L.; Licchelli, M.;
Monzani, E. Org. Biomol. Chem. 2005, 3, 1495-1500. (i) Cho, E. J.; Ryu,
B. J.; Lee, Y. J.; Nam, K. C. Org. Lett. 2005, 7, 2607-2609. (j) Esteban-
Go´mez, D.; Fabbrizzi, L.; Licchelli, M. J. Org. Chem. 2005, 70, 5717-
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(25) Liu, B.; Tian, H. J. Mater. Chem. 2005, 15, 2681-2686.

5930 Organometallics, Vol. 26, No. 24, 2007
Zhao et al.
tion of this orbital, which is believed to be responsible for the
obvious red shift of emission wavelength.
completely and the solution colors of 1-3 changed from yellow-
green to brown, which can be observed with the naked eye.
From the calculated binding constant values, we can see that
1-3 prefer to bind F- and CH3COO- over H2PO4-. Especially,
1 prefers to bind F- over the other anions, suggesting that 1
can act as an ideal phosphorescent chemosensor for F-. This
preliminary understanding of the anion-sensing mechanism will
actually help in the design of a series of new phosphorescent
probes based on iridium(III) complexes by simply modifying
the chemical structures of the ligands to contain a specific
recognition site, which will also help in the exploration for new
applications of iridium(III) complexes in chemosensors.
In addition, the electrochemical properties of 1-3 were also
investigated upon addition of CF3COOH (Figure 9 and Sup-
porting Information). No evident variations of oxidation waves
were observed for 1 and 2. However, for complex salt 3, the
oxidation wave assigned to the carbazole fragment disappeared.
This fact indicated that the carbazole fragment was also
protonized after addition of CF3COOH and the protonation made
the oxidation of the carbazole fragment more difficult. More-
over, upon addition of CF3COOH, the reduction waves of 1-3
assigned to the reduction of the N∧N ligands were markedly
shifted positively. So, protonation of the N∧N ligand can reduce
the energy levels of the LUMO more significantly and decrease
the energy of the triplet excited state, which is consistent with
the result of theoretical calculations.
Acknowledgment. The authors acknowledge the financial
support of National Natural Science Foundation of China
(20490210 and 20501006), National High Technology Program
of China (2006AA03Z318), and Shanghai Science and Technol-
ogy Community (05DJ14004 and 06QH14002).
Conclusions
In conclusion, we have synthesized a series of new cationic
iridium(III) complex salts containing different imidazo[4,5-f]-
[1,10]phenanthroline derivatives. The influences of anions and
proton on the photophysical and electrochemical properties were
studied in detail. After the addition of CF3COOH, the emission
wavelengths of the three complex salts 1-3 were significantly
red-shifted and the emission colors changed from yellow to red.
In addition, upon addition of F-, CH3COO-, and H2PO4-, the
emission of the three complex salts 1-3 was quenched
Supporting Information Available: Photoluminescent spectra
and cyclic voltammograms of 1-5, response of absorption and
photoluminescence spectra upon titration with anions and CF3-
COOH, and cyclic voltammograms of 2 and 3 before and after
addition of F- and CF3COOH. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM700623J