A novel multifunctional cyclometallated iridium(III) complex with interesting second-order nonlinear optical properties and two-photon absorption activity

Article abstract of DOI:10.1016/j.poly.2017.12.009

A novel cationic cyclometallated Ir(III) complex, namely [Ir(C^N-ppy-4-CH[dbnd]CHC₆H₄NEt₂)₂(N^N-bpy-CH[dbnd]CHC₆H₄NEt₂)][PF₆] (ppy = 2-phenylpyridine; bpy = 2,2′-bipyridine), was prepared and well characterized. Its good second-order NLO response, as determined in solution by the EFISH technique, and its interesting two-photon absorption activity, as measured by the Z-scan technique in the femtosecond case, make it a good candidate for application in photonics and biomedicine.

Full text of DOI:10.1016/j.poly.2017.12.009

Accepted Manuscript
A novel multifunctional cyclometallated iridium(III) complex with interesting
second-order nonlinear optical properties and two-photon absorption activity
Alessia Colombo, Eleonora Garoni, Claudia Dragonetti, Stefania Righetto,
Dominique Roberto, Nicolò Baggi, Muriel Escadeillas, Véronique Guerchais,
Kenji Kamada
PII:
S0277-5387(17)30791-X
https://doi.org/10.1016/j.poly.2017.12.009
POLY 12965
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
6 October 2017
6 December 2017
Please cite this article as: A. Colombo, E. Garoni, C. Dragonetti, S. Righetto, D. Roberto, N. Baggi, M. Escadeillas,
V. Guerchais, K. Kamada, A novel multifunctional cyclometallated iridium(III) complex with interesting second-
order nonlinear optical properties and two-photon absorption activity, Polyhedron (2017), doi: https://doi.org/
10.1016/j.poly.2017.12.009
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A novel multifunctional cyclometallated iridium(III) complex with
interesting second-order nonlinear optical properties and two-photon
absorption activity.
Alessia Colombo,a,b,c Eleonora Garoni,a,e Claudia Dragonetti,*a,b,c Stefania Righetto,a,b
Dominique Roberto,a,b,c Nicolò Baggi,a Muriel Escadeillas,d Véronique Guerchais,*d and
Kenji Kamada*e
b
aDip. di Chimica dell’Università degli Studi di Milano, UdR di Milano dell’INSTM, cIstituto
d
di Scienze e Tecnologie Molecolari del CNR, via Golgi, 19, I-20133 Milano, Italy; Institut
des Sciences Chimiques de Rennes UMR 6226 CNRS-Université de Rennes 1, Campus de
e
Beaulieu, 35042 Rennes Cedex, France; IFMRI, National Institute of Advanced Industrial
Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan.
Corresponding authors: claudia.dragonetti@unimi.it, veronique.guerchais@univ-rennes1.fr,
k.kamada@aist.go.jp
Abstract
A
novel cationic cyclometallated Ir(III) complex, namely [Ir(C^N-ppy-4-
CH=CHC6H4NEt2)2(N^N-bpy-CH=CHC6H4NEt2)][PF6] (ppy= 2-phenylpyridine; bpy= 2,2’-
bipyridine), was prepared and well characterized. Its good second-order NLO response, as
determined in solution by the EFISH technique, and its interesting two-photon absorption
activity, as measured by the Z-scan technique in the femtosecond case, make it a good
candidate for application in photonics and biomedicine.
Keywords: Second-order nonlinear optics; EFISH; two-photon absorption activity;
cyclometallated iridium(III) complexes.
1

Introduction
Coordination compounds with both luminescent and second-order nonlinear optical
(NLO) properties are of great interest as multifunctional materials, as they may offer
additional flexibility, when compared to organic NLO chromophores, by introducing new
NLO active electronic charge-transfer transitions between the metal and the ligand, tuneable
by virtue of the nature, oxidation state and coordination sphere of the metal centre [1,2].
Cyclometallating ligands are often incorporated in Ir(III) complexes for various applications
such as in organic light-emitting diodes (OLEDs) [3], light-emitting electrochemical cells
(LEECs) [4], and dye-sensitized solar cells (DSSCs) [5]. Whereas cyclometallated Ir(III)
complexes have been intensively studied for their interesting luminescent properties, to our
knowledge, only a few reports appeared in the literature on their second-order NLO properties
[6, 7] or two-photon absorption (TPA) activity [8-11]. Yet, two-photon absorbing materials
having large two-photon absorption cross-section (σ), especially in the near-infrared (NIR)
region, are required for photodynamic therapy, bio-imaging, upconversion lasing and drug
delivery [9] whereas the design of novel second-order NLO active compounds is crucial for
many applications in the fields of optical communication and data processing [2]. Beeby and
co-workers reported a series of iridium(III) acetylacetonate complexes, bearing two
cyclometallated substituted 2-phenylpyridines, characterized by fair values of TPA cross
sections (approximatively 20 GM) [10]. Another report concerning iridium complexes of a
terpyridyl-stilbene system demonstrated TPA cross-sections in the range of 10-70 GM [11].
More recently, Das and co-workers reported the synthesis of cyclometallated iridium(III)
complexes containing two cyclometallated unsubstituted 2-phenylpyridines and a 2,2’-
bipyridine bearing highly π-delocalized substituents with TPA cross-sections in the range of
45-196 GM in the femtosecond case [8c]. Besides, some of us reported that iridium(III)
acetylacetonate complexes bearing two substituted cyclometallated 4-styryl-2-
phenylpyridines are characterized by a good second-order NLO response [7f], as determined
by means of the Electric Field Induced Second Harmonic generation (EFISH) technique [12].
Remarkably, the simple luminescent cyclometallated Ir(III) complex [Ir(C^N-ppy-4-
CH=CHC6H4NEt2)2(acetylacetonate)] (ppy = 2-phenylpyridine) [13] shows a µ
= -550 x
1.907
10-48 esu and is a useful tool for the preparation of NLO active polymeric films [7f]. These
interesting results prompted us to investigate the effect of the substitution of the
acetylacetonate ligand by a π-delocalized bipyridine incorporating electron-donor substituents
on the second-order NLO response. Therefore, we prepared the novel cationic cyclometallated
2

Ir(III) complex [Ir(C^N-ppy-4-CH=CHC6H4NEt2)2(N^N-bpy-CH=CHC6H4NEt2)][PF6] (5)
(bpy=bipyridine; Figure 1) and studied its luminescent and NLO properties. Its second-order
NLO response was measured in solution through the EFISH technique, working with an
incident and non resonant wavelength of 1907 nm, whereas its two-photon absorption activity
was evaluated by the Z-scan technique in the femtosecond case.
Figure 1. Investigated cyclometallated Ir(III) complex (5)
Material and methods
Synthesis
General comments
All reagents were purchased from Sigma-Aldrich and were used without further purification.
1
Reactions requiring anhydrous conditions were performed under nitrogen. H NMR spectra
were recorded at 400 MHz on a Bruker AVANCE-400 instrument; chemical shifts (δ) are
expressed in ppm relative to internal Me4Si as standard; signals were abbreviated as s, singlet;
bs, broad singlet; d, doublet; t, triplet; q, quartet; m, multiplet. The UV-Vis spectra of the
samples solution in dichloromethane were recorded by a Shimadzu UV-3150 spectrometer
using 1 cm quartz cells. Elemental analysis was carried out with a PerkinElmer CHN 2400
instrument of the Department of Chemistry at the University of Milan. Steady state emission
and excitation spectra and photoluminescence lifetimes were obtained with an FLS 980
spectrofluorimeter (Edinburg Instrument Ltd.). Continuous excitation for the steady state
measurements was provided by a 450 W xenon arc lamp. Photoluminescence lifetime
measurements were performed using an Edinburgh Picosecond Pulsed Diode Laser EPL-445
(Edinburg Instrument Ltd.), with a central wavelength of 442.2 nm and repetition rates of 20
MHz, by a time-correlated single-photon counting method. Mass spectrum was measured
with a LCQ fleet ion trap mass Spectrometer (ESI-MS).
3

4-Methyl-2-phenylpyridine (1). An excess of lithium (1.82 g, 272 mmol) was suspended in
40 mL of Et2O. The suspension was cooled down to 0 °C and bromobenzene (21.34 g, 136
mmol) in 50 mL of Et2O was added dropwise during 20 minutes. The reaction mixture was
stirred overnight at room temperature. The freshly-prepared phenyllithium was added
dropwise to a solution of 4-picoline (3.16 g, 34 mmol) in 90 mL toluene. The reaction was
stirred at 30°C for 24 hours, distilled water was added dropwise, the residue was extracted
with CH2Cl2, washed with water, dried over MgSO4 and the solvent was removed under
reduced pressure. The product was purified by column chromatography (silica, n-
1
heptane:AcOEt=9:1) to afford 1 as an orange/brown solid (2.44 g). Yield: 42%. H-NMR
(400 MHz, CDCl3) δ (ppm): 8.58 (1H, d, J = 5.0 Hz), 8.00 (2H, d, J = 7.2 Hz), 7.57 (1H, s),
7.49 (2H, t, J = 7.4 Hz), 7.43 (1H, t, J = 7.2 Hz), 7.08 (1H, d, J = 4.9 Hz), 2.44 (3H, s).
4-N,N-diethylminostyryl-2-phenylpyridine (2). 4-Methyl-2-phenylpyridine (500 mg, 2.96
mmol), 4-N,N-diethylaminobenzaldehyde (620 mg, 3.5 mmol) and t-BuOK (700 mg, 6.2
mmol) were dissolved in DMF (20 mL). The reaction mixture was heated at reflux overnight,
then CH2Cl2 (150 mL) was added. The organic phase was washed first with water and then
with an aqueous solution of 1 M KOH, dried with MgSO4 and the solvent was removed under
reduced pressure. The crude product was purified by column chromatography (silica,
1
CH2Cl2:petroleum ether = 7:3) to obtain 2 as a yellow powder (546 mg). Yield: 56%. H
NMR (400 MHz, CDCl3) δ (ppm): 8.61 (1H, d, J = 5.2 Hz), 8.06 (2H, d, J = 7.2 Hz), 7.75
(1H, s) 7.51 (2H, t, J = 7.4 Hz), 7.45 (3H, d, J = 8.5 Hz), 7.30 (1H, d, J = 16.3 Hz), 7.26 (1H,
m), 6.86 (1H, d, J = 16.2 Hz), 6.68 (2H, d, J = 8.8 Hz), 3.40 (4H, q, J = 7.1 Hz), 1.20 (6H, t, J
= 7.0 Hz).
[Ir(C^N-ppy-4-CH=CHC6H4NEt2)2Cl]2 (3). IrCl3 • 3H2O (165 mg, 0.55 mmol) and 2 (550
mg, 1.66 mmol) were suspended in a mixture of 2-ethoxyethanol:H2O 3:1 (16 mL) in a
Schlenk tube under inert atmosphere. The reaction mixture was heated at reflux for 24 h. The
precipitate was decanted by centrifugation and the solid product was then washed
successively with H2O, EtOH and Et2O. The solvent was removed with cannula to afford 3 as
1
an orange powder (290 mg). Yield: 30%. H-NMR (400 MHz, CD2Cl2) δ (ppm): 9.12 (4H, d,
J = 5.9 Hz), 7.94 (4H, s), 7.63 (4H, d, J = 7.1 Hz), 7.41 (12H, m), 7.04 (4H, d, J = 16 Hz),
6.93 (4H, m), 6.83 (4H, t, J = 7.0 Hz), 6.64 (12H, m), 6.05 (4H, d, J = 8.0 Hz), 3.48 (16H, q, J
= 6.8 Hz), 1.25 (24H, t, J = 6.8 Hz).
4,4'-p-[(N,N-diethyl)aminostyryl]-2,2'-bipyridine (4). Diisopropylamine (607.1 mg, 6
mmol) was dissolved in THF (2.5 mL) in a Schlenk tube and the mixture was cooled to 0°C.
4

A n-BuLi solution (1.6 M in hexane, 3.75 mL, 6 mmol) was added slowly. After stirring one
hour, the solution was cooled to -78 °C and 4,4’-dimethyl-2,2’-bipyridine (501.1 mg, 2.72
mmol) in THF (13 mL) was added dropwise and the mixture stirred at low temperature for 2
hours. p-(N,N-diethyl)aminobenzaldehyde (957.1 mg, 5.4 mmol) was dissolved in 6 mL of
THF (6 mL) and added slowly. The resulting mixture was stirred for one hour at low
temperature and overnight at room temperature. After hydrolyzing with distilled water (12
mL), the phases were separated, the organic phase was dried over MgSO4, filtered and the
solvent was removed under reduced pressure. The dialcohol was dissolved in toluene (40 mL)
in a round-bottomed flask and pyridinium p-toluenesulfonate (PPTS, 67.6 mg, 0.27mmol)
was added. The mixture was heated at reflux for 4 hours. After cooling to room temperature,
the solvent was removed under reduced pressure and dichloromethane (16 mL) was added.
The mixture was washed with a saturated solution of NaHCO3. The precipitated bipyridine
was filtered, abundantly washed first with H2O and then with Et2O to obtain 4 as an orange
powder (970 mg). Yield: 71%. 1H-NMR (400 MHz, CDCl3) δ (ppm):8.63 (2H, d, J = 5.1 Hz),
8.48 (2H, s), 7.47 (4H, d, J = 8.9 Hz), 7.42 (2H, d, J = 16.2 Hz), 7.36 (2H, dd, J = 5.3, 1.8
Hz), 6.92 (2H, d, J = 16.2 Hz), 6.71 (4H, d, J = 8.9 Hz), 3.43 (8H, q, J = 7.1 Hz), 1.22 (12 H,
t, J = 7.1 Hz).
[Ir(C^N-ppy-4-CH=CHC6H4NEt2)2(N^N-bpy-CH=CHC6H4NEt2)][PF6] (5). A suspension
of 3 (250 mg, 0.14 mmol), 4 (178 mg, 0.35 mmol) and AgPF6 (88 mg, 0.35 mmol) in 1,2-
dichloroethane (20 mL) was kept at reflux for 2 hours and stirred at room temperature for 16
hours. The solvent was removed under reduced pressure leaving a residue which was washed
with Et2O (3 x 20 mL). The compound was precipitated from Et2O/CH2Cl2 giving the desired
complex (5) as a red solid after filtration (50 mg). Yield: 13%. 1H NMR (500 MHz, CD2Cl2) δ
(ppm): 8.32 (2H, s), 7.93 (2H, s), 7.84 (2H, d, J = 5.7 Hz), 7.80 (2H, d, J = 7.4 Hz), 7.42
(18H, m,), 7.08 (2H, t, J = 7.7 Hz), 7.02 (2H, d, J = 4.5 Hz), 6.95 (2H, m), 6.86 (2H, d, J =
16.0 Hz), 6.68 (8H, dd, J = 16, 8.9 Hz), 6.46 (2H, d, J = 7.9 Hz), 3.41 (16H, m), 1.20 (24H,
m). ESI-MS (positive mode in CH2Cl2) m/z = 1349,63 [M-PF6]+. Elem. Anal. Calcd for
C80H84F6IrN8P: C, 64.28; H, 5,66; N, 7.50. Found: C, 64.34; H, 5.67; N, 7.51.
EFISH measurements
EFISH measurements [12] were carried out at the Dipartimento di Chimica of the Università
di Milano, in CH2Cl2 solutions at a concentration of 1 x 10–3 M, working with an incident
non-resonant wavelength of 1.907 µm, obtained by Raman-shifting the fundamental 1.064 µm
wavelength produced by a Q-switched, mode-locked Nd3+:YAG laser manufactured by
5

Atalaser. The apparatus for the EFISH measurements is a prototype made by SOPRA
(France). The reported µβEFISH values are the mean values of 16 successive measurements
performed on the same sample. The sign of µβ is determined by comparison with the
reference solvent (CH2Cl2).
Two-photon absorption activity measurements
All open-aperture Z-scan measurements [14] were performed at AIST in Osaka, for the
solution of the complex 5 held in a 2-mm quartz cuvette. The setup for the Z-scan
measurements were reported elsewhere [15]. A femtosecond, wavelength-tunable laser
(optical parametric amplifier, SpectraPhysics TOPAS Prime) was employed as light source to
obtain the spectrum. Typical pulsewidth was 120 fs and the repetition rate was 1 kHz. First,
the outline of the TPA spectrum was measured at a single excitation power (0.4 mW,
corresponding to the on-axis optical intensity at the focal point of 99-150 GW/cm2) by
assuming that the observed open-aperture Z-scan signal originates from the TPA process
(open dots in Fig. 4). Then the assumption was confirmed and the precise value of the TPA
cross section (σ(2)) were obtained by changing the excitation power (filled dots with
experimental errors in Fig. 4 Fig. 3). Finally, the relative TPA spectrum (open dots) were
superimposed the absolute TPA spectrum (filled dots). For all measurements, in-house
standard compounds (MPPBT [16] in DMSO) was measured at the same condition and used
for the spectral correction of σ(2).
Results and Discussion
The complex [Ir(C^N-ppy-4-CH=CHC6H4NEt2)2(N^N-bpy-CH=CHC6H4NEt2)][PF6]
(5) was prepared as shown in Scheme 1.
6

•
Scheme 1. (i) t-BuOK, DMF, 155 °C, 15 h; (ii) IrCl3 3H2O, 2-ethoxyethanol/H2O, 100 °C, 24 h; (iii) a) n-BuLi,
iPr2NH, p-(N,N-diethyl)aminobenzaldehyde, THF, 0 °C → -78°C → rt, 15 h; b) PPTS, toluene, 110°C, 4 h; (iv)
AgPF6, 1,2-dichloroethane, 84 °C, 2 h → rt, 15 h.
The pro-ligand 4-(N,N-diethyl)aminostyryl-2-phenylpyridine (2) was readily prepared upon
deprotonation of the methyl group of 4-methyl-2-phenylpyridine, obtained by reaction of
phenyllithium
with
4-picoline,
followed
by
condensation
with
p-(N,N-
diethyl)aminobenzaldehyde, as previously reported [13]. Heating at reflux this pro-ligand
with IrCl3 • 3H2O in a 2-ethoxyethanol:H2O 3:1 mixture for 24 h afforded the related µ-
dichloro-bridged cyclometallated iridium dimer intermediate (3) [13]. The ancillary ligand
4,4'-p-[(N,N-diethyl)aminostyryl]-2,2'-bipyridine (4) was prepared like 2 but starting from
4,4’-dimethyl-2,2’bipyridine [17]. The desired complex (5) was finally obtained by refluxing
in 1,2-dichloroethane for 2 hours this π-delocalized substituted bipyridine with the µ-
dichloro-bridged cyclometallated iridium dimer. It was obtained as a dark red powder and
well characterized (see Material and methods).
The absorption spectrum of complex 5 was registered both in dichloromethane and
dimethyl sulfoxide (DMSO, Figure 2a) whereas the photophysical data are listed in Table 1.
By analogy with other cationic iridium(III) complexes bearing two cyclometallated
7

phenylpyridines and a bipyridine [6e], the absorption bands under 350 nm can reasonably be
1
assigned to (π-π*) transitions of the styrylphenylpyridine and styrylbipyridine ligands, the
intense band between 350 and 550 nm can be assigned to an Intra-Ligand Charge Transfer
(ILCT) transition in which the pyridyl moiety acts as a π*-acceptor group hiding the (d(Ir) →
π*(ppy/bpy)) MLCT band, while the weak band centered at 620 nm may be due to direct
population of triplet charge transfer states [6e]. A pronounced solvatochromic behavior is
observed going from DMSO to CH2Cl2, typical of electronic transitions with an appreciable
degree of charge-transfer character; the blue shift of the band with increasing solvent polarity
suggests a lower dipole moment in the excited state than in the ground state [18].
a)
b)
Figure 2. a) Superposition of absorption spectra of complex 5 in DMSO (red) and CH2Cl2 (blue); b)
Excitation spectrum at 77 K (blue line), emission spectrum at 298 K (black line) and emission spectrum at
77 K (red line), all in a degassed 5x10-5 M THF solution of 5 (λexc = 450 nm).
The normalized photoluminescence (PL) spectra of 5 in degassed THF at 298 K and at 77 K
are shown in Figure 2b and the data are summarized in Table 1. The novel complex is only
very weakly emissive in fluid solution at room temperature (Fig. 3b 2b), because the radiative
decay is quenched by the known competitive non-radiative E-Z isomerization process of the
C-C double bond, triggered by excitation with light before emission, of bipyridines linked to
an Ir(III) center [6e, 19].
8

λ
abs / nm
µβ1.907 /x10-48 esuc
λem/nmb
τ/µsb
(ε / M-1cm-1)a
454 (6450)
-960
669, 736
57
Table 1. Photophysical data for complex 5. [a] In CH2Cl2 solution at 298 K; in DMSO: λabs = 440 nm, ε × 103 =
5.37 M-1cm-1. [b] In THF at 77 K (λexc = 460 nm). [c] In CH2Cl2 solution (10−3M); uncertainty in EFISH
measurements is 10%
On the other hand, 5 is emissive at 77 K in THF, the luminescence spectrum is highly
structured and the emission is located in the red region of the visible spectrum, as predicted
upon incorporation of extended π-conjugated substituents in the ligands. With reference to
previously reported Ir(III) complexes bearing two cyclometallated phenylpyridines and one
bipyridine [6e], considering the highly structured spectrum and the long lifetime (57 µs),
luminescence can be assigned to radiative decay from a triplet state predominantly localized
on the same ligand, rather than from the MLCT state. In any case the participation of the
metal in the emission is necessary to promote the population of the formally forbidden triplet
emissive state.
The quadratic hyperpolarizability of complex 5 was measured by the solution phase
direct current EFISH generation method,which can provide direct information on the intrinsic
molecular NLO properties through eq 1:
γ
EFISH = (µβλ/5kT) + γ(-2ω;ω,ω, 0)
(1)
where µβλ/5kT is the dipolar orientational contribution and γ(-2ω; ω, ω, 0) is the third-order
polarizability corresponding to the mixing of two optical fields at ω and the dc poling field at
ω=0. This latter term is often referred as the electronic cubic contribution to γ EFISH, which is
usually negligible. βλ is the projection along the dipole moment (µ) axis of the vectorial
component of the tensor of the quadratic hyperpolarizability at the incident wavelength λ. All
EFISH measurementswere carried out working in CH Cl solutions at a concentration of 10–3
2
2
M, with a non resonant incident wavelength of 1.907 µm, obtained by Raman-shifting in a
high pressure H of the fundamental 1.064 µm wavelength produced by a Q-switched, mode-
locked Nd3+:YAG laser.
2
It turned out that complex 5 is characterized by a negative value of µβ1.907 (-960x10-48 esu,
Table 1) in agreement with the observed solvatochromic behavior and with a negative value
of ∆µeg (difference of the dipole moment in the excited and ground state) upon excitation [2].
9

It is worth pointing out that the absolute µβ1.907 value of complex 5 is almost twice that
reported for related [Ir(C^N-ppy-4-CH=CHC6H4NEt2)2(acetylacetonate)] (ppy = 2-
phenylpyridine) [7e] suggesting that 4,4'-p-[(N,N-diethyl)aminostyryl]-2,2'-bipyridine is much
better than acetylacetonate as ancillary ligand in this kind of cyclometallated Ir(III) complexes
for second-order nonlinear optics.
Complex 5 was then investigated for its two-photon absorption activity. It was
dissolved in DMSO (0.55 mM) and studied with the z-scan technique in the femtosecond case.
The TPA spectrum is shown in Figure 3.
Figure 3. The OPA (line) and TPA (dots) spectra of complex 5.
Remarkably, the two-photon absorption cross-sections are quite high, in the range 100-250
GM at 600-1000 nm. Contrarily to previously reported TPA active cationic iridium(III)
complexes having two cyclometallated unsubstituted 2-phenylpyridines and a 2,2’-bipyridine
bearing highly π-delocalized substituents [8c], the complex investigated here has less
extended substituents on the bipyridine but it bears them also on the 2-phenylpyridine ligands.
The excellent correspondence of the observed TPA peak with the wavelength-doubled one-
photon absorption peak, as shown in Figure 4 3, suggests that the TPA peak mainly originates
from the dipolar contribution [20] governed by asymmetric charge transfer, similar to the
EFISH property. In this way, the charge-transfer property and the extended π-conjugation
10

over the whole molecule results in good TPA properties of 5 compared to the previously
reported complexes of similar structures. Besides, it is worth pointing out that some
iridium(III) complexes bearing two cyclometallated unsubstituted 2-phenylpyridines and a 2-
phenylimidazo[4,5-f][1,10]phenanthroline, characterized by two-photon absorption cross-
sections in the range 48.8-65.5 GM at 750 nm, were utilized as efficient agents for
mitochondrial imaging and tracking in living cells under two-photon (750 nm) excitation [21].
Similarly, complex 5 can find application in biomedical research.
Conclusion
In conclusion, our work put in evidence how a careful choice of the coordination sphere of
cyclometallated iridium(III) complexes can lead to high second-order nonlinear optical
properties and two-photon absorption activity, correlated through the charge-transfer
character of the complex. Substitution of acetylacetonate by
a
4,4'-p-[(N,N-
diethyl)aminostyryl]-2,2'-bipyridine is a simple way to increase the second-order NLO
response in this kind of cyclometallated Ir(III) complexes. In addition the use of simple π-
delocalized donor substituents on both the cyclometallated 2-phenylpyridine and 2,2’-
bipyridine allows to reach high two-photon absorption sections in a wide range of
wavelengths. Clearly the novel complex reported here has a great potential for application in
photonics and biomedicine.
Acknowledgements
This work was supported by MIUR, in Italy, and by a Grant-in-Aid for Scientific Research on
Innovative Areas “Photosynergetics” (No. JP26107004, K.K.) from MEXT and a Grant-in-
Aid for Scientific Research (No. JP25248007, K.K.) from JSPS, Japan. We thank CNRS for a
financial support (PICS Rennes-Milan) and l’Università Italo Francese (Progetto Galileo
2015/2016; G15_50) for mobility support. Regione Lombardia and Fondazione Cariplo are
gratefully acknowledged for the use of instrumentation purchased through the SmartMatLab
Centre project (2014). We thank Dr. Daniele Marinotto for luminescence and lifetime
measurements.
11

References
[1] J. Zyss, Molecular Nonlinear Optics: Materials, Physics and Devices, Academic Press,
Boston, 1994.
[2] (a) B.J. Coe, in Comprehensive Coordination Chemistry II; Vol. 9, Elsevier Pergamon:
Oxford, U.K., 2004. (b) B.J. Coe, N.R.M Curati, Comments on Inorg. Chem. 25 (2004) 147-
184. (c) O. Maury, H. Le Bozec, Acc. Chem. Res. 38 (2005) 691-704. (d) C.E. Powell, M.G.
Humphrey, Coord. Chem. Rev. 248 (2004) 725-756. (e) E. Cariati, M. Pizzotti, D. Roberto, F.
Tessore, R. Ugo, Coord. Chem. Rev. 250 (2006) 1210-1233 (f) B. J. Coe, Acc. Chem. Res. 39
(2006) 383-393. (g) M.G.Humphrey, M. Samoc, Adv. Organomet. Chem. 55 (2007) 61-136.
(h) J. Boixel, V. Guerchais, H. Le Bozec, A. Chantzis, D. Jacquemin, A. Colombo, C.
Dragonetti, D. Marinotto, D. Roberto Chem.Comun. 51 (2015) 7805-7808.
(i) S. Di Bella, C. Dragonetti, M. Pizzotti, D. Roberto, F. Tessore, R. Ugo in Topics in
Organometallic Chemistry 28. Molecular Organometallic Materials for Optics, Vol. 28 (Eds:
H. Le Bozec, V. Guerchais), Springer, 2010, 1-55. (l) O. Maury, H. Le Bozec, in Molecular
Materials; D.W. Bruce, D. O’Hare and R.I. Walton, Eds.; Wiley: Chichester, 2010, 1-59.
[3] (a) R.C. Evans, P. Douglas, C.J. Winscom, Coord. Chem Rev. 250 (2006) 2093-2126 and
references therein. (b) L. Flamigni, A. Barbieri, C. Sabatini, B.Ventura, F. Barigelletti, Top.
Curr. Chem. 281 (2007) 143-203.(c) G. Zhou, W.Y. Wong S. Suo, J. Photochem. Photobio.
C: Photochem. Rev. 11 (2010) 133-156. (d) W.Y. Wong, C.L. Ho, Coord. Chem. Rev. 253
(2009) 1709-1758. (e) W.Y. Wong, C.L. Ho, J. Mater. Chem. 19 (2009) 4457-4482. (f) G.
Zhou, W.Y. Wong, X. Yang, Chem. Asian J. 6 (2011) 1706-1727. (g) H. Wu, G. Zhou, J.
Zou, C.L. Ho, W.Y. Wong, W. Yang, J. Peng, Y. Cao, Adv. Mater. 21 (2009) 4181-4184.
[4] (a) J.D. Slinker, J. Rivnay, J.S. Moskowitz, J.B. Parker, S. Bernhard, H.D. Abruna, G.G.
Malliaras, J. Mater. Chem. 17 (2007) 2976-2988. (b) E. Zysman-Colman, J.D. Slinker, J.B.
Parker, G.G. Malliaras, S. Bernhard, Chem. Mater. 20 (2008) 388-396. (c) H.J. Bolink, L.
Cappelli, E. Coronado, M. Graetzel, E. Ortı´, R.D. Costa, M. Viruela, M.K. Nazeeruddin, J.
Am. Chem. Soc. 128 (2006) 14786-14787. (d) E. Margapoti, V. Shukla, A. Valore, A.
Sharma, C. Dragonetti, C. Kitts, D. Roberto, M. Murgia, R. Ugo M. Muccini, J. Phys. Chem.
C 113 (2009) 12517-12522. (e) W.Y. Wong, G.J. Zhou, X.M. Yu, H.S. Kwok, Z. Lin, Adv.
Funct. Mater. 17 (2007) 315-323. (f) E. Margapoti, M. Muccini, A. Sharma, A. Colombo, C.
Dragonetti, D. Roberto, A. Valore, Dalton. Trans. 41 (2012) 9227-9231. (g) N.M. Shavaleev,
R. Scopelliti, M. Graetzel, M.K. Nazeeruddin, A. Pertegas, C. Roldan-Carmona, D. Torderab,
H.J. Bolink, J. Mater. Chem. C, 1 (2013) 2241-2248. (h) A. F. Henwood, E. Zysman-Colman,
12

Top. Curr. Chem. 374:36 (2016) 1-41. (i) R. D. Costa, E. Ortí, H. J. Bolink, F. Monti, G.
Accorsi, N. Armaroli, Angew. Chem., Int. Ed. 51 (2012) 8178-8211.
[5] (a) E.I. Mayo, K. Kilsa T. Tirrell, P.I. Djurovich, A. Tamayo, M.E. Thompson, N.S.
Lewis, H.B. Gray, Photochem. Photobiol. Sci. 5 (2006) 871-873. (b) E. Baranoff, J.H. Yum,
M. Graetzel, Md.K. Nazeeruddin, J. Organomet. Chem. 694 (2009) 2661-2670. (c) E.
Baranoff, J.H. Yum, I. Jung, R. Vulcano, M. Graetzel, Md.K. Nazeeruddin, Chem. Asian J. 5
(2010) 496-499. (d) Y. Shinpuku, F. Inui, M. Nakai, Y. Nakabayashi, J. Photochem. and
Photobio. A: Chemistry 222 (2011) 203-209. (e) C. Dragonetti, A. Valore, A. Colombo, S.
Righetto, V. Trafiletti, Inorg. Chim. Acta 388 (2012) 163–167.
[6] (a) C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, A. Valore, S. Fantacci, A. Sgamellotti,
F. De Angelis, Chem. Commun. (2007) 4116-4118. (b) C. Dragonetti, S. Righetto, D.
Roberto, A. Valore, T. Benincori, F. Sannicolò, F. De Angelis, S. Fantacci, J Mater Sci: Mater
Electron 20 (2009) S460–S464. (c) C. Dragonetti, S. Righetto, D. Roberto, A. Valore, Phys.
Status Solidi, C6, No. S1 (2009) S50–S53. (d) A. Valore, E. Cariati, C. Dragonetti, S.
Righetto, D. Roberto, R. Ugo, F. De Angelis, S. Fantacci, A. Sgamellotti, A. Macchioni, D.
Zuccaccia, Chem. Eur. J. 16 (2010) 4814-4825. (e) V. Aubert, L. Ordronneau, M. Escadeillas,
J.A.G. Williams, A. Boucekkine, E. Coulaud, C. Dragonetti, S. Righetto, D. Roberto, R. Ugo,
A. Valore, A. Singh, J. Zyss, I. Ledoux-Rak, H. Le Bozec, V. Guerchais, Inorg. Chem. 50
(2011) 5027-5038.
[7] (a) A. Valore, A. Colombo, C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, F. De Angelis,
S. Fantacci, Chem. Commun. 46 (2010) 2414–2416. (b) C. Dragonetti, S. Righetto, D.
Roberto, R. Ugo, A. Valore, F. Demartin, F. De Angelis, A. Sgamellotti, S. Fantacci, Inorg.
Chim. Acta 361 (2008) 4070–4076. (c) C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, A.
Valore, I. Ledoux-Rak, Nonlinear Optics, Quantum Optics 43 (2012) 197-204. (d) M. Zaarour,
V. Guerchais, H. Le Bozec, C. Dragonetti, S. Righetto, D. Roberto, F. De Angelis, S. Fantacci,
M.G. Lobello, Dalton Trans. 42 (2013) 155–159. (e) M. Zaarour, A. Singh, C. Latouche,
J.A.G. Williams, I. Ledoux-Rak, J. Zyss, A. Boucekkine, H. Le Bozec, V. Guerchais, C.
Dragonetti, A. Colombo, D. Roberto, A. Valore, Inorg. Chem. 52 (2013) 7987–7994. (f) C.
Dragonetti, A. Colombo, D. Marinotto, S. Righetto, D. Roberto, A. Valore, M. Escadeillas, V.
Guerchais, H. Le Bozec, A. Boucekkine, C. Latouche, J. Organometal. Chem. 751 (2014)
568-572.
[8] (a) Y. Fan, D. Ding, D. Zhao, Chem. Commun. 51 (2015) 3446. (b) C.-L. Ho, K.-L. Wong,
H.-K. Kong, Y.-M. Ho, C. T.-L. Chan, W.-M. Kwok, K. S.-Y. Leung, H.-L. Tam, M. H.-W.
Lam, X.-F. Ren, A.-M. Ren, J.-K. Feng, W.-Y. Wong, Chem. Commun. 48 (2012) 2525–2527.
13

(c) M. Sarma, T. Chatterjee, R. Bodapati, K. N. Krishnakanth, S. Hamad, S. V. Rao, S. K.
Das, Inorg. Chem. 55 (2016) 3530-3540. (d) W.-J Xu, S.-J. Liu, X. Zhao, N. Zhao, Z.-Q. Liu,
H. Xu, H. Liang, Q. Zhao, X.-Q. Yu, W. Huang, Chem. Eur. J. 19 (2013) 621. (e) C. Jin, J.
Liu, Y. Chen, L. Zeng, R. Guan, C. Ouyang, L. Ji, H. Chao, Chem. Eur. J. 21 (2015) 12000.
[9] (a) M. Pawlicki, H. A. Collins, R. G. Denning, H. L. Anderson, Angew. Chem. Int. Ed. 48
(2009) 3244-3266. (b) L. K. McKenzie, I. V. Sazanovich, E. Baggaley, M. Bonneau, V.
Guerchais, J. A. G. Williams, J. A. Weinstein, H. E. Bryant, Chem. Eur. J. 23 (2017) 234-238.
[10] R. M. Edkins, S.L. Bettington, A.E. Goeta, A. Beeby, Dalton Trans. 40 (2011) 12765.
[11] L.S. Natrajan, A. Toulmin, A. Chew, S.W. Magennis, Dalton Trans. 39 (2010) 10837.
[12] (a) B. F. Levine, C. G. Bethea, Appl. Phys. Lett. 24 (1974) 445-447. (b) K. D. Singer, A.
F. Garito, J. Chem. Phys. 75 (1981) 3572-3580. (c) I. Ledoux, J. Zyss, J. Chem. Phys. 73
(1982) 203-213.
[13] M. Lepeltier, T. K:-M. Lee, K. K.-W. Lo, L. Toupet, H. Le Bozec, V. Guerchais, Eur. J.
Inorg. Chem. (2007) 2734-2747.
[14] M. Sheik-Bahae, A. A. Said, T.-H. Wei, D. G. Hagan, E. W. van Stryland, IEEE J. Quant.
Electr. 26 (1990) 760–769.
[15] K. Kamada, K. Matsunaga, A. Yoshino, K. Ohta, J. Opt. Soc. Am. B 20 (2003) 529–537.
[16] K. Kamada, Y. Iwase, K. Sakai, K. Kondo, K. Ohta, J. Phys. Chem. C 113 (2009)
11469–11474.
[17] T. Le Bouder, L. Viau, J.-P. Guégan, O. Maury, H. Le Bozec, Eur. J. Org. Chem. (2002)
3024-3033
[18] E. Rossi, A. Colombo, C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, A. Valore, J.A.G.
Williams, M.G. Lobello, F. De Angelis, S. Fantacci, I. Ledoux-Rak, A. Singh, J. Zyss Chem.
Eur. J. 19 (2013) 9875-9883.
[19] A. Colombo, C. Dragonetti, D. Roberto, A. Valore, C. Ferrante, I. Fortunati, A. L. Picone,
F. Todescato, J. A. G. Williams, Dalton Trans. 44 (2015) 15712-15720.
[20] K. Kamada, Disp. Imag.,1(2014) 107–130.
[21] C. Jin, J. Liu, Y. Chen, L. Zeng, R. Guan, C. Ouyang, L. Ji, and H. Chao, Chem. Eur. J.
21 (2015) 12000-12010.
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A novel easily-prepared cationic cyclometallated Ir(III) complex is characterized by a good
second-order NLO response, as determined in solution by the EFISH technique, and by
interesting two-photon absorption activity, as measured by the Z-scan technique in the
femtosecond case. It is a good candidate for application in photonics and biomedicine.
15