Preparation and photophysical properties of mixed-ligand cyclometallated complexes of Ir(III) with a dendritic bipyridine ligand

Article abstract of DOI:10.1007/s11176-005-0295-x

Complexes [Ir(C∧N)₂(G1-bpy)]PF₆, where C∧N is a cyclometallating ligand derived from 2-(2′-thienyl)pyridine and 2-phenylpyridine, and G1-bpy is a dendritic bipyridine ligand of the first generation, 4,4′-bis[3″,5″-bis(benzyloxy)pheny

Full text of DOI:10.1007/s11176-005-0295-x

Russian Journal of General Chemistry, Vol. 75, No. 5, 2005, pp. 665 671. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 5, 2005,
pp. 705 711.
Original Russian Text Copyright
2005 by Kulikova, McClenaghan, Balashev.
Preparation and Photophysical Properties
of Mixed-Ligand Cyclometallated Complexes of Ir(III)
with a Dendritic Bipyridine Ligand
M. V. Kulikova*, N. McClenaghan**, and K. P. Balashev*
* Herzen Russian State Pedagogical University, St. Petersburg, Russia
** University of Messina, Messina, Italy
Received January 15, 2004
Abstract Complexes [Ir(C^N)2(G1-bpy)]PF6, where C^N is a cyclometallating ligand derived from 2-(2 -
thienyl)pyridine and 2-phenylpyridine, and G1-bpy is a dendritic bipyridine ligand of the first generation,
4,4 -bis[3",5"-bis(benzyloxy)phenylethyl]-2,2 -bipyridine, were prepared and characterized by 1H NMR,
electronic absorption, and emission spectroscopy. The polyether dendritic substituents exert a soft effect on
the spectral and luminescence properties of the complexes, manifested as slight destabilization of the elec-
tronically excited charge-transfer state involving the bipyridine ligand, as compared to the model complexes
[Ir(C^N)2(bpy)]PF6.
Bis- and triscyclometallated Ir(III) complexes at-
properties of the related mixed-ligand biscyclometal-
tract increased researchers’ attention owing to the lated complexes of Ir(III) containing a 4,4 -substituted
possibility of using them as phosphorescing materials
in organic light-emitting devices (OLEDs) [1 3]. In
these devices, singlet and triplet excited states arising
from charge recombination are trapped with a chro-
mophore in which fast intercombination conversion
results in room-temperature electrophosphorescence.
dendritic bipyridine ligand. The choice of polyether
dendritic substituents is governed, on the one hand,
by their donor power and, on the other hand, by the
possibility of specific solvation of the bipyridine
moiety. Both these factors can affect the energy of the
excited charge-transfer state involving the bipyridine
One of the factors governing the performance of phos- ligand.
phorescing OLEDs is the spin orbital coupling caus-
The dendritic bipyridine ligand was prepared ac-
cording to [7] (Scheme 1).
ing the singlet triplet mixing of the excited states of
the chromophore. As compared to Ru(II) and Os(II)
complexes, Ir(III) complexes (d6) are characterized by
higher quantum yields of the luminescence in liquid
solutions at room temperature {for example [4],
In the first step, 4,4 -dimethyl-2,2 -bipyridine reacts
with excess lithium diisopropylamide in anhydrous
THF at 10 C. The resulting 4,4 -bis(lithiomethyl)-
2,2 -bipyridine reacts with dendritic benzyl bromide
in THF. The disubstituted dendritic bipyridine ligand
and the monosubstituted product can be subsequently
separated by column chromatography.
of (fac-[Ir(ppy)3] is 0.4, where ppy is 2-phenylpyrpidhoi-s
nate). This is due to efficient intercombination conver-
sion between the singlet and triplet excited states,
caused by spin orbital coupling in the Ir(III) ion.
1
In mixed-ligand biscyclometallated complexes of
the type [Ir(C^N)2(bpy)]PF6 [here C^N is 2-(2 -thien-
yl)pyridinate (tpy) or 2-phenylpyridinate (ppy); bpy is
The H NMR spectrum of the resulting dendritic
bipyridine ligand confirms its symmetrical structure
(see Experimental). In particular, the bipyridine moie-
2,2 -bipyridine], studied in [5, 6], the orbital nature of ty gives three proton signals, the integral intensity of
the luminescing state strongly depends on the solvent
polarity and matrix hardness. Colombo et al. [5, 6]
believe that this effect, especially in the case of the
phenylpyridinate complex, is due to the fact that the
intraligand excited state and the charge-transfer state
involving, respectively, the cyclometallating and bi-
pyridine ligands have close energies. Therefore, it is
interesting to study the spectral and luminescence
each of them corresponding to 2H, i.e., the related
hydrogen atoms of the two pyridine rings are equiva-
lent. At the same time, in the monosubstituted deriva-
tive, the protons in positions 3 and 3 , and in positions
5 and 5 are nonequivalent and give separate signals.
The protons in positions 6 and 6 , more remote from
the dendritic substituent, are less sensitive to the sub-
stitution.
1070-3632/05/7505-0665 2005 Pleiades Publishing, Inc.

666
KULIKOVA et al.
Scheme 1.
m
p
0
THF
O
O
O
10 C
o
p
CH2Li
CH2Li
O
O
O
3
3
5
6
5
Br
N
N
6
N
N
C6H14NLi
CH3
G1-bpy
H3C
N
N
1
In the H NMR spectrum of the dendritic bipyri-
dine, the proton signals are shifted upfield as com-
pared to unsubstituted 2,2 -bipyridine (by 0.16 ppm
on the average), which reflects the donor power of the
dendritic substituent.
With a CH2Cl2 CH3OH mixture as solvent, the
chloride ligands in the dimeric complex can be readily
substituted by the dendritic N^N bipyridine ligand
under mild conditions and with a high product yield
(62 67%). This route was used previously for prepar-
ing [Rh(ppy)2(bpy)]+ [8]. The reaction course and the
purity of the target product were monitored by thin-
layer chromatography on Al2O3 plates with CH2Cl2
CH3OH, 20 : 1, as eluent.
The starting compounds for preparing mixed-ligand
cyclometallated complexes [Ir(C^N)2(G1-bpy)]+ are
the dimeric complexes [Ir(C^N)2Cl]2 prepared by the
published procedure (Scheme 2).
Scheme 2.
O
O
N
N
Ir
N
N
N
N
C
C
C
Cl
Cl
C
G1-bpy
2IrCl3 nH2O + 4HC^N
Ir
N
C
C
N
O
O
3
S
.
C
N =
N
N
6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 5 2005

PREPARATION AND PHOTOPHYSICAL PROPERTIES
667
1
1
1
Table 1. H chemical shifts ( , ppm, relative to TMS) and H 1H coupling constants (J, Hz) in the H NMR spectra of
the complexes [Ir(C^N)2(G1-bpy)]+ in CD2Cl2
Atom in (C^N)2Ir fragment
Compound
3
4
5
6
3
4
5
6
[Ir(ppy)2Cl]2
7.94
7.80
6.83
9.25
(3J 5.1,
4J 1.5)
5.87
(3J 7.8,
4J 0.9)
6.33
6.82
(3J 7.8,
7.2)
6.61
(3J 7.8,
7.2)
7.56
(3J 7.5) (3J 7.5, 8.1, (3J 6.0, 7.4,
(3J 7.7)
4J 1.5)
7.78
4J 1.5)
6.99
[Ir(ppy)2
(bpy)]+a
[Ir(ppy)2
7.95
7.51
6.93
7.07
7.74
(3J 8.2) (3J 8.3, 7.4) (3J 7.3, 5.6)
(3J 5.5)
7.41 7.27 m
(3J 7.5) (3J 7.5, 7.4) (3J 7.5, 7.9) (3J 7.8)
7.89
7.64
6.88
(3J 7.5, 6.1)
6.67
6.28
7.06
6.93
7.71
(G1-bpy)]+ (3J 7.8) (3J 8.4, 7.4)
(3J 7.7)
(3J 7.6) (3J 8.1, 7.5) (3J 7.8)
[Ir(tpy)2Cl]2
7.56
7.68
9.00
5.89b (3J 4.8)
7.12c (3J 4.8)
(3J 8.0, (3J 8.4, 6.9) (3J 7.4, 5.9)
4J 1.5)
(3J 5.9)
[Ir(tpy)2
7.52
7.40 7.28 m
6.72 6.67 m
7.52
6.28 (3J 4.8)
7.44 (3J 4.8)
(G1-bpy)]+
bpy
5,5
G1
CH2O
Compound
3,3
6,6^
Ph
CH2 CH2
[Ir(ppy)2(bpy)]+a
9.29 (3J 7.8) 7.45(3J 7.3, 5.6) 7.97 (3J 5.7)
[Ir(ppy)2(G1-bpy)]+ 8.25 s
7.12 (3J 5.4) 7.81 (3J 5.7) 7.41 7.27m, 6.48 6.45m
4.99 3.14 3.11 m,
2.98 2.93 m
4.99 3.18 3.12 m,
2.99 2.94 m
[Ir(tpy)2(G1-bpy)]+ 8.26 s
7.16 (3J 5.7) 7.76 (3J 5.7) 7.40 7.28m, 6.49 6.47m
a
b
c
Data from [9].
1
4 -H.
5 -H.
The main H NMR parameters (chemical shifts and
H6 protons of the C^N ligand are appreciably shielded,
which is due to the anisotropic effect of the pyridine
rings of the bipyridine ligand. On the other hand, the
H3 protons of the ppy ligand and H4 protons of the
tpy ligand in [Ir(C^N)2(G1-bpy)]PF6 are less shielded
than the corresponding protons in the dimeric com-
plexes because of the absence of -donor chloride
ligands in the trans position. The coordination shifts
coupling constants JHH) of the complexes [Ir(C^N)2
(G1-bpy)]PF6 are given in Table 1. For comparison
we also give data for the corresponding ( -Cl)-dimer-
ic complexes and published data for [Ir(ppy)2(bpy)]+
1
[9]. The H NMR data for [Ir(tpy)2(bpy)]+ are not
given in Table 1, because Colombo and Gudel [5]
gave only the general view of the spectrum. According
1
to the H NMR spectrum (Fig. 1), the related protons
=
for the H3,3 and H5,5 protons of the
lig
of the two cyclometallating ligands in the complexes
[Ir(C^N)2(G1-bpy)]+ are equivalent, which indicates
that the complex is highly symmetrical. The starting
dimeric complexes [Ir(C^N)2Cl]2 also give first-order
1H NMR spectra. Taking into account the crystallo-
graphic data available for [Ir(ppy)2Cl]2 [10] and
[Ir(ppy)2(acac)] (here acac is acetylacetonate) [2] and
mild conditions of the synthesis of the complexes
[Ir(C^N)2(G1-bpy)]PF6, we can conclude that the
pyridine rings of the two cyclometallating ligands in
[Ir(ppy)2(G1-bpy)]PF6 and [Ir(tpy)2(G1-bpy)]PF6 are
arreanged trans to each other. As compared to the
( -Cl)-dimeric complexes, in the corresponding
mononuclear complexes [Ir(C^N)2(G1-bpy)]PF6 the
bipyridcinomepmoiety of the dendritic ligand in the com-
plexes [Ir(C^N)2(G1-bpy)]PF6 are close to zero,
whereas for H6,6 this shift is about 0.8 ppm. Such a
shielding is due to the anisotropic effect of the ring
current in the pyridine ring of the cyclometallating
ligand. On the whole, the coordination shifts
in the
complexes [Ir(C^N)2(G1-bpy)]PF6 are smaller than in
the related complexes with unsubstituted 2,2 -bipyri-
dine. The largest difference in
H3,3 protons in the bipyridine moiety of the com-
plexes [Ir(ppy)2(G1-bpy)]+ and [Ir(ppy)2(bpy)]+
is observed for the
(
0.07 and 0.86 ppm, respectively). This may be due
to the van der Waals interaction of the H3 and H3
protons, enhanced by dendritic substituents. It is
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668
KULIKOVA et al.
CH2O
G1
G1
CH2 CH2
3.0
5.0
4.5
4.0
3.5
6,6 ppy
5 ppy
5 ppy
4 ppy
3,3 ppy
6 ppy
4 ppy
3 ppy
3 ppy
5,5 ppy
8.4
8.2
8.0
7.8
7.6
7.4
7.2
7.0
6.8
6.6
6.4
6.2
, ppm
1
Fig. 1. H NMR spectrum of [Ir(ppy) (G1-bpy)]PF in CD Cl .
2
6
2
2
interesting that, in the related tpy complexes, the
difference in
of the H3 and H3 protons is consid-
erably smaller ( 0.06 and 0.06 ppm).
was observed previously [13] with Pt(II) tpy com-
plexes compared to the ppy complexes. As seen from
Table 2, the position of the low-energy spin-forbidden
transition is sensitive to the structure of the noncyclo-
metallating ligand. An increase in the ligand donor
power causes a bathochromic shift of this band from
463 to 492 nm. This fact suggests that the low-energy
spin-forbidden transition involving the cyclometallat-
ing ligand is essentially an MLCT transition.
The parameters of the electronic absorption spec-
tra of the complexes [Ir(C^N)2(G1-bpy)]PF6 in di-
chloromethane at room temperature are given in
Table 2 together with published data for some other
cyclometallated Ir(III) complexes. The electronic ab-
sorption spectra of the related complexes [Ir(C^N)2
(G1-bpy)]PF6 and [Ir(C^N)2(bpy)]PF6 are similar.
In the UV range of the spectra, there is a strong band
with a vibronic structure at 277 345 nm for the tpy
complex and 260 340 nm for the ppy complex, origi-
nating from the spin-allowed intraligand transitions
involving the cyclometallating and bipyridine ligands.
The spin-allowed metal-to-ligand charge-transfer
(MLCT) transitions are observed at 380 430 nm.
Taking into account the electrochemical data for the
complexes [Ir(C^N)2(bpy)]+ [8] and the assignment
of the related absorption bands for the complexes
[Pt(C^N)(bpy)]+ [12], we can expect lower energy of
the MLCT transition involving the bipyridine ligand.
The spectrum of [Ir(ppy)2(G1-bpy)] contains also the
bands of spin-forbidden transitions at 437 ( 1200)
and 469 nm ( 580). Relatively high intensity of these
transitions is due to strong spin orbital coupling
caused by the Ir(III) ion. These low-energy transitions
are not manifested in the absorption spectrum of the
corresponding tpy complex, probably because of
lower molar extinction coefficients. A similar pattern
Similarly to the previously studied complexes
[Ir(C^N)2(bpy)]+, the luminescence behavior of the
complexes [Ir(C^N)2(G1-bpy)]+ strongly depends on
the matrix [dichloromethane or poly(methyl methac-
rylate)] and temperature (298 or 77 K) (Table 3,
Fig. 2). Such a dependence was not observed with
mixed-ligand Ir(III) phenylpyridinate complexes with
N^N,C-coordinated ligands derived from 6-phenyl-
2,2 -bipyridine [14]. Therefore, as a basis for inter-
pretation of the luminescence data we chose a model
suggested by Colombo et al. [5, 6] for Ir(III) com-
plexes with unsubstituted bipyridine. According to this
model, the close energies of the two low-lying excited
states and the purer MLCT character of the elec-
tronically excited state involving the bipyridine ligand
allow the stability of this excited state to be varied in
a wide range by varying the polarity or hardness of
the matrix. Depending on the conditions, the lowest
3
excited state is either the (IL/MLCT) (IL is intralig-
and transition) state involving the cyclometallating
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PREPARATION AND PHOTOPHYSICAL PROPERTIES
669
3
Table 2. Electronic absorption spectra of mixed-ligand
the (d Ir
* ) type. The position of the maxi-
N^N
cyclometallating complexes of Ir(III) in dichloromethane
mum and the shape of the luminescence band are sim-
ilar to those characteristic of other Ir(III) phenylpyri-
dinate complexes with polypyridine ligands. Introduc-
tion of dendritic substituents led to a hypsochromic
shift of the maximum of the charge-transfer lumines-
cence band compared to [Ir(ppy)2(bpy)]+, which is
consistent with the donor nature of the substituents.
Furthermore, the effect of dendritic substituents is
manifested in going to hard matrices. Whereas in the
luminescence spectrum of [Ir(ppy)2(bpy)]+ the super-
position of two types of luminescence bands in poly-
(methyl methacrylate) was observed only at 10 K, in
the spectrum of [Ir(ppy)2(G1-bpy)]+ the second lumi-
nescence component at 480 nm is detected even at
room temperature. Another evidence is the nonexpo-
nential decay of the luminescence. Similar behavior is
observed in glassy matrices at 77 K; the short-wave
maximum (470 nm) of the arising luminescence band
overlaps with the low-energy band in the absorption
3
Compound
max, nm ( 10 )
[Ir(tpy)2(G1-bpy)]+ 277 (48.8), 308 sh (34.2), 331 sh
(15.1), 417 (9.3)
[Ir(tpy)2(bpy)]+a
[Ir(tpy)2Cl]2
279 (46.3), 310 sh (30.6), 417 (8.9)
290 (47.9), 403 (10.8), 454 (8.6)
302 (25.1), 336 (12.6), 387 (6.3),
453 (3.2)
[Ir(tpy)2(acac)]b
[Ir(ppy)2(G1-bpy)]+ 262 (48.1), 309 sh (20.1), 338 sh
(9.2), 357 (6.9), 381 (5.7), 413 sh
(3.1), 437 (1.2), 469 (0.58)
[Ir(ppy)2(bpy)]+c
265 (36.1), 310 (16.1), 335 sh, 375
(4.7), 410 (2.8), 465 (0.58)
260 (41.7), 337 (8.5), 384 (5.8),
433 sh (0.43), 463 (0.21)
(Bu4N)[Ir(ppy)2
(CN)2]d
(Bu4N)[Ir(ppy)2
266 (38.9), 335 (6.7), 355 (5.3), 400
(3.4), 437 (2.3), 476 (0.65)
260 (49.0), 356 (8.2), 403 (4.7),
450 (3.2), 492 (1.0)
(NCS)2]d
[Ir(ppy)2(acac)]e
(a)
5
[Ir(ppy)2Cl]2
260 (68.0), 335 (13.0), 355 sh
(11.0), 400 (6.3), 434 (4.2), 484 (1.1)
I
II
2
4
3
1
a
b
Data from [5].
Data from [8].
Data from [1], 2-methyltetrahydrofuran.
d e
3
c
Data from [11].
Data from [2].
Table 3. Luminescence characteristics of the complexes
2
1
[Ir(C^N)2(N^N)]+
4
max, nm ( , s)
Compound
poly(methyl C2H5OH
methacry- CH3OH
late), 298 K CH2Cl2, 77K
0
5
CH2Cl2,
298 K
(b)
I
II
3
[Ir(ppy)2(G1-bpy)]+ 562 (<1) 480 sh,
470,
4
3
523 (1.7)a
532
524 sh (4.3)a
524 (4.8)
2
[Ir(ppy)2(bpy)]+b 585
[Ir(tpy)2(G1-bpy)]+ 544 sh,
585(5.1)a
540 (10.1) 535 (17.3)
2
1
[Ir(tpy)2(bpy)]+c
600
541
532 (17)d
1
a
Nonexponential luminescence decay; the long-lived com-
b
ponent of the luminescence signal is indicated. Data from
0
c
d
[6, 8].
Data from [5].
[Rh(ppy) (bpy)]PF matrix.
2 6
250 350 450 550 650 750
, nm
3
ligand or the MLCT (d Ir
* ) state. However,
N^N
nonuniform distribution of complex species in solution
can lead to a boundary situation, superposition of two
types of luminescence. In particular, in a dichloro-
methane solution at room temperature, the lowest
electronically excited state of [Ir(ppy)2(G1-bpy)]+
responsible for the luminescence can be assigned to
Fig. 2. (I) Absorption spectra in dichloromethane and
(II) luminescence spectra of (a) [Ir(ppy) (G1-bpy)]PF
2
6
and (b) [Ir(tpy) (G1-bpy)]PF . Solvent (matrix):
2
6
(1) C H OH CH OH CH Cl , 4 : 1 : 1, 77 K;
2
5
3
2
2
(2) poly(methyl methacrylate), 298 K; and (3) CH Cl ,
2
2
298 K.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 5 2005

670
KULIKOVA et al.
spectrum. The range 470 515 nm and the lifetime
( 1 5 s) are typical of the luminescence from the
electronically excited state of the (IL/MLCT) type
involving the ppy ligand in phenylpyridinate com-
plexes of both Ir(III) [2, 11] and Pt(II), containing no
polypyridine ligand N^N.
The dendritic bipyridine ligand G1-bpy was pre-
pared according to [7]. A 2 M solution of lithium
diisopropylamide in THF heptane (1.4 ml) was added
at 10 C to a solution of 171 mg of 4,4 -dimethyl-
2,2 -bipyridine in anhydrous THF. After stirring for
45 min, a solution of 1 g of 3,5-bis(benzyloxy)benzyl
bromide in 30 ml of anhydrous THF was added. The
resulting solution was stirred for 12 h at room tem-
perature. When the solution became light yellow, the
reaction was considered to be complete. The resulting
solution was poured onto ice, and the aqueous layer
was extracted with dichloromethane (5 50 ml). The
extract was dried over Na2SO4. The solvent was evap-
orated on a rotary evaporator, and the residue was
chromatographed on SiO2 (eluent dichloromethane
ethyl acetate, 5 : 1 by volume). Fractions with Rf 0.5
(TLC on SiO2 plates, eluent dichloromethane meth-
anol, 20 : 1) were combined, and the solvents were
removed on a rotary evaporator. The reaction product
was dissolved in diethyl ether, precipitated with eth-
3
It is known that tpy complexes are characterized by
1
larger (by 3000 cm on the average) singlet triplet
splitting than the corresponding ppy complexes [6,
13]. This accounts for the larger energy gap between
the electronically excited state involving the cyclo-
3
metallating ligand and the MLCT (d Ir
* )
state. As a result, in hard matrices [e.g., poly(meNth^Nyl
methacrylate)], even at room temperature, only the
3(IL/MLCT) state in [Ir(tpy)2(G1-bpy)]+ and [Ir(tpy)2
(bpy)]+ is luminescing, with a characteristic shape of
the luminescence band. Dendritic substituents exert an
additional effect in dichloromethane solutions at room
temperature. Appearance of a shoulder at 544 nm in
the luminescence spectrum of [Ir(tpy)2(G1-bpy)]+,
absent in the spectrum of [Ir(tpy)2(bpy)]+ taken under
the same conditions, and the nonexponential lumines-
cence decay suggest superposition of two types of
luminescence bands, as it was recorded for the corre-
sponding ppy complex in a poly(methyl methacrylate)
matrix at 298 K.
1
anol, filtered off, and vacuum-dried. Yield 23%. H
NMR spectrum (CDCl3), , ppm (J, Hz): 8.59 (H6,6
,
5
3JHH 5.0, JHH 0.9), 8.32 (H3,3
,
5JHH 0.9), 7.46
7.35 m (Ho,m,p), 7.12 (H5,5
,
3JHH 5.1), 6.52 (Hp ,
4
4JHH 2.1), 6.49 (Ho , JHH 2.1), 3.01 2.97 m (CH2
CH2), 5.03 s (CH2O).
Thus, the luminescence behavior of mixed-ligand
cyclometallated Ir(III) complexes with a dendritic
bipyridine ligand strongly depends on the structure of
the cyclometallating ligand (effect through the sing-
let triplet splitting energy), temperature, and matrix
(effect of the hardness and polarity). Introduction of
dendritic substituents can be considered as one more
influencing factor; polyether dendritic substituents in
positions 4 and 4 of the bipyridine ligand exert a
soft effect on the spectral and luminescence proper-
ties of the complexes [Ir(C^N)2(G1-bpy)]PF6, mani-
fested in slight destabilization of the electronically
excited charge-transfer state involving the bipyridine
ligand, compared to the model complexes [Ir(C^N)2
(bpy)]PF6.
[Ir(ppy)2(G1-bpy)]PF6. To a solution of 30 mg of
G1-bpy in CH2Cl2 CH3OH (5 : 6) we added 20.7 mg
of [Ir(ppy)2Cl]2. The mixture was refluxed for 12 h.
The reaction progress was monitored by TLC (SiO2,
CH2Cl2 CH3OH, 20 : 1). The final solution was
cooled to room temperature, and the solvents were
removed on a rotary evaporator. The residue was
dissolved in a minimal volume of methanol and fil-
tered; a saturated solution of NH4PF6 in methanol
was added to the filtrate. The resulting yellow precip-
itate was filtered off, washed with diethyl ether, and
vacuum-dried; yield 62%.
[Ir(tpy)2(G1-bpy)]PF6 was prepared similarly from
30 mg of G1-bpy and 20.9 mg of [Ir(tpy)2Cl]2. Yield
67%.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Bruker
Aspect-300 spectrometer at 298 K. The electronic
absorption spectra were taken on a Kontron-Uvikon-
860 spectrophotometer. Luminescence measurements
were performed with a Spex-Jobin Yvon-Fluoromax-2
fluorimeter and a KSVU-1 installation (LGI-21 nitro-
ACKNOWLEDGMENTS
The authors are grateful to staff members of Prof.
S. Campagna’s laboratory (University of Messina,
Italy) for the assistance in the study.
gen pulse laser,
337 nm,
10 ns).
exc
pulse
The study was financially supported by the Minis-
try of Education of the Russian Federation (grant for
young scientists no. PD02-1.3-15).
Syntheses were performed in an inert atmosphere.
The starting dimeric complexes [Ir(C^N)2Cl]2 were
prepared according to [5].
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