Novel ruthenium(II) complexes with substituted 1,10-phenanthroline or 4,5-diazafluorene linked to a fullerene as highly active second order NLO chromophores

Article abstract of DOI:10.1039/c0dt00686f

Various Ru(II) complexes with substituted 1,10-phenanthroline or 4,5-diazafluorene are characterized by a good to very large second order NLO response, as determined by EFISH. Among these complexes, [Ru(9-fulleriden-4,5- diazafluorene)(PPh₃)₂Cl₂] is particularly appealing due to its huge second-order NLO response and its transparency to the second harmonic generation. The structure of cis-Cl,trans-PPh ₃-[Ru(5-NO₂-1,10-phen)(PPh₃)₂Cl ₂)] was determined by single-crystal X-ray diffraction. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00686f

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Novel ruthenium(II) complexes with substituted 1,10-phenanthroline or
4,5-diazafluorene linked to a fullerene as highly active second order NLO
chromophores†
Adriana Valore,a Marcella Balordi,a Alessia Colombo,a Claudia Dragonetti,a Stefania Righetto,a
Dominique Roberto,*a,b Renato Ugo,a,b Tiziana Benincori,b,c Giovanni Rampinini,d Francesco Sannicolo`*d and
Francesco Demartine
Received 19th June 2010, Accepted 2nd August 2010
DOI: 10.1039/c0dt00686f
Various Ru(II) complexes with substituted 1,10-phenanthroline or 4,5-diazafluorene are characterized
by a good to very large second order NLO response, as determined by EFISH. Among these complexes,
[Ru(9-fulleriden-4,5-diazafluorene)(PPh3)2Cl2] is particularly appealing due to its huge second-order
NLO response and its transparency to the second harmonic generation. The structure of
cis-Cl,trans-PPh3-[Ru(5-NO2-1,10-phen)(PPh3)2Cl2)] was determined by single-crystal X-ray diffraction.
tional electron withdrawing C60-fullerene system.6 Therefore we
Introduction
investigated 4,5-diazafluorene as the ligand to which the C60 unit
Coordination complexes with second-order non-linear optical
is connected through a cyclopropane group, which allows a facile
(NLO) properties are of particular interest as new molecular ma-
electronic communication between the fullerene and the ligand
terials for electro-optical and optical applications.1 In particular,
the presence of a metal centre can offer electronic flexibility by
introducing charge-transfer transitions, metal to ligand (MLCT)
or ligand to metal (LMCT), usually at low energy and of relatively
high intensity, tunable by virtue of its nature, oxidation state and
coordination sphere, or by shifting to lower energy the internal
charge transfer transitions (ILCT) of organic push-pull ligands.2
Recently, we reported3 that various cationic cyclometallated
Ir(III) complexes with a substituted 1,10 phenanthroline show one
of the highest second-order NLO responses (measured as mb1.907 by
the Electric Field Induced Second Harmonic generation (EFISH)
method)4 reported for metal complexes. Such a high response
was attributed mainly to a MLCT process from the orbitals of
the cyclometallated Ir(III) system, acting as the donor, to the
p* orbitals of the phenanthroline ligand, acting as the acceptor
system.3
(periconjugation).7
Results and discussion
We prepared, characterized and investigated the second-order
NLO properties of all of the Ru(II) complexes reported in Fig. 1.
These findings and the observation that the presence of a redox-
active metal centre such as Ru(II) could provide a redox-switchable
modulation of the NLO responses,5 prompted us to investigate
the second-order non linear optical properties of some neutral
Ru(II) complexes with substituted 1,10-phenanthroline or 4,5-
diazafluorene. In particular it was appealing to investigate the
effect on the p* acceptor properties of the 4,5-diazafluorene ligand
of a substituent such as the highly polarisable and non conven-
aDip. CIMA “Lamberto Malatesta” dell’Universita` degli Studi di Milano,
UdR dell’INSTM and,
Fig. 1 General structure of the investigated Ru(II) NLO chromophores.
bISTM-CNR, V. Venezian 21, 20133 Milano, Italy. E-mail: dominique.
roberto@unimi.it; Fax: +39-02-50314405; Tel: +39-02-50314399
The known complexes trans-Cl,cis-CO-[Ru(1,10-phen)(CO)2-
Cl2]8 (1a, phen = phenanthroline) and cis-Cl,trans-PPh3-[Ru(1,10-
phen)(PPh3)2Cl2)]9 (2a) and the new complexes trans-Cl,cis-CO-
[Ru(5-NO2-1,10-phen)(CO)2Cl2)] (1b), cis-Cl,trans-PPh3-[Ru(5-
NO2-1,10-phen)(PPh3)2Cl2)] (2b) and cis-Cl,trans-PPh3-[Ru(4,7-
diphenyl-1,10-phen)(PPh3)2Cl2] (2c) were prepared by reac-
tion of [Ru(CO)2Cl2]n or [Ru(PPh3)3Cl2] with the substituted
1,10-phenanthroline following the synthetic procedure reported
cDipartimento di Scienze Chimiche ed Ambientali dell’Universita`
dell’Insubria, Via Valleggio 11, 22100, Como, Italy
dDipartimento di Chimica Organica e Industriale dell’Universita` degli Studi
di Milano, via Venezian 21, 20133 Milano, Italy
eDipartimento di Chimica Strutturale
e Stereochimica Inorganica
dell’Universita` degli Studi di Milano, via Venezian 21, 20133 Milano, Italy
† CCDC reference number 780726. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt00686f
10314 | Dalton Trans., 2010, 39, 10314–10318
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in the literature10–11 (see Experimental). The new complexes
trans-Cl,cis-CO-[Ru(4,5-diaz)(CO)2Cl2] (3, diaz = diazafluorene),
cis-Cl,trans-PPh3-[Ru(4,5-diaz)(PPh3)2Cl2)] (4), trans-Cl,cis-CO-
[Ru(9-fulleriden-4,5-diaz)(CO)2Cl2] (5) and cis-Cl,trans-PPh3-
[Ru(9-fulleriden-4,5-diaz)(PPh3)2Cl2] (6) were prepared in the
same way by reaction with 4,5-diazafluorene12 or 9-fulleriden-4,5-
diazafluorene.13 The geometry of the various isomers was estab-
lished on the basis of IR and NMR evidence (see Experimental).14
The structure of complex 2b was determined by single-crystal
X-ray diffraction and has been shown to contain the octahedral
Ru(II) ion surrounded by two trans triphenylphospine ligands, two
cis chloride ions and the phenanthroline ligand in the equatorial
plane of the octahedron (See Fig. 2).
reported for dp → pp* MLCT transitions from Ru(II) to pyridine,
bipyridine or phenanthroline ligands.10,14 When a C60 fullerene
moiety is linked to the 4,5-diazafluorene ligand (5 and 6), the
band below 350 nm becomes strong due to the presence of the
fullerene moiety,15 while the band at around 479–482 nm is, as for
1a and 2a, 1b and 2b, 3 and 4, much stronger in the presence of
two phosphines (6) instead of two CO (5) (Table 1).
The second-order NLO response was determined as mb1.907
values by means of the EFISH technique4 working in DMF
solution with a non resonant incident wavelength of 1.907 mm.
As shown in Table 1, all complexes show a negative good to large
value of mb1.907 (-600 to -3435 ¥ 10-48 esu). The negative sign of
mb1.907 is in agreement with a reduction of the dipole moment in
the excited state due to MLCT transitions, which dominate the
second order NLO response.2
It must be noticed that the second-order NLO response of
complexes with 1,10-phenanthroline as the chelating ligand is
much higher for complexes 2a, 2b and 2c, carrying two triph-
enylphosphines instead of two CO (1a, 1b) as ancillary ligands. It
is similar in the case of complexes with 4,5-diazafluorene as the
chelating ligand (compare 3 with 4 and 5 with 6). The rather low
second-order NLO response of complexes with two CO ligands,
such as 1a, 1b and 3 (mb1.907 from -600 ¥ 10-48 esu to -730 ¥
10-48 esu), appears to be quite independent of the nature of the
chelating ligand (4,5-diazafluorene or 1,10-phenanthroline).
The second-order NLO response of complexes 1a, 1b and 3 is
reasonably attributed mainly to MLCT transitions from the metal
to the p* aromatic system of the 1,10-phenathroline or of the 4,5-
diazafluorene. The relevant increase (by a factor of 2–3) of the
second-order NLO response observed upon substitution of the
“Ru(CO)2Cl2” moiety by “Ru(PPh3)2Cl2”, as in the case of 2a, 2b,
4, could be explained by an increase of b1.907 due to an increase
of the electronic density and consequently of the donor properties
of the Ru centre involved in the MLCT transitions controlling
the quadratic hyperpolarizability b1.907. The determination of
the dipole moment of 1b and 2b by the Guggenheim method16
confirms this suggestion since b1.907 increases by a factor of 3.8
moving from 1b (b1.907 = -77 ¥ 10-30 esu, m = 9.4 ¥ 10-18 esu) to 2b
(b1.907 = -291 ¥ 10-30 esu, m = 7.6 ¥ 10-18 esu).
Fig. 2 ORTEP view of Complex 2b. Displacement ellipsoids are drawn
at 30% probability.
The trends of the electronic spectra of the prepared complexes
are, as expected, similar to those reported for this kind of complex14
(Table 1). In the case of 1a, 1b, and 3, with two cis CO ligands,
there is a band below 350 nm typical of internal pp → pp*
transitions of the aromatic system of 1,10-phenanthroline or
4,5-diazafluorene together, at lower energy, with a broad weak
shoulder (366–380 nm). A relatively strong band (459–507 nm) is
typical of complexes 2a, 2b, 2c, and 4, with two trans phosphine
ligands. These absorptions at relatively low energy are in the range
Table 1 Absorption maxima and mb1.907 values of Ru(II) complexes
Differently from 1a and 1b, a significant enhancement of the
absolute value of mb1.907 is observed on moving from 2a to 2b
(mb1.907 = -1585 ¥ 10-48 and -2210 ¥ 10-48 esu, respectively). Such a
trend was previously reported for the cationic complexes of Ir(III),
[Ir(phenylpyridine)2(5-R-1,10-phen][PF6]3 and was attributed to
an increase of the acceptor properties of the p* orbitals of the
1,10-phenanthroline bearing the NO2 group and therefore to a
more facile MLCT transition. Moreover, as for the case of these
cationic Ir(III) complexes,3 the second-order NLO response of
2c carrying the more polarisable 4,7-diphenyl-1,10-phen ligand
(mb1.907 = -2030 ¥ 10-48 esu) is high and comparable to that of 2b
(mb1.907 = -2210 ¥ 10-48 esu).
It is relevant that the presence of a fullerene group on the 4,5-
diazafluorene ligand leads to a huge increase of the mb1.907 value
(from -600 ¥ 10-48 esu for 3 to -2800 ¥ 10-48 esu for 5). Moreover, as
when comparing 1a and 2a, substitution of the “Ru(CO)2Cl2” (5)
by the “Ru(PPh3)2Cl2” (6) moiety affords an additional increase
of the mb1.907 value (-3435 ¥ 10-48 esu).
Absorption maximaa/
Complex
nm [e/M-1 cm-1]
EFISH mb1.907a,b/10-48 esu
1a
1b
2a
2b
2c
272 [8400]
370 (sh, w, br)
273 [25 500]
380 (sh, w, br)
271 [39 500]
329 (sh, vw), 459 [4900]
273 [35 100]
336 (sh, vw), 507 [5000]
276 [33 700]
345 (sh, vw), 475 [10 200]
319 [11 200], 366 (sh, w)
272 [27 300], 355 (sh, w),
474 [3300]
-696
-730
-1585c
-2210c
-2030c
3
4
-600
-1040
5
6
257 [104 800]
322 (sh, w), 479 [2200]
260 [395 800]
-2800
-3435
325 (sh, w), 482 [10 600]
a In DMF. b By using 10-3M solutions, the error of EFISH measurements
is 10%. c Similar values are obtained working in CHCl3 at the same
concentration.
Remarkably, the high absolute value of mb1.907 of 5 and 6,
when compared to that of 3 and 4 (Table 1), clearly evidences
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the important role of the fullerene group in enhancing the NLO
response. This effect cannot be explained by a particularly strong
electron-accepting ability of the fullerene (there is only a small red
shift in the MLCT band on going from 4 to 6) but can be attributed
to its large polarizability.
Trans-Cl,cis-CO-[Ru(1,10-phen)(CO)2Cl2] (1a). The poly-
meric precursor [Ru(CO)2Cl2]n (76 mg, 0.33 mmol) and the 1,10-
phenanthroline ligand (65 mg, 0.36 mmol) were dissolved in 20 mL
of degassed CH3OH and the mixture was heated under reflux.
After 1 h the orange solution became cloudy and an orange-
yellow powder appeared. The solid was filtered off, washed with
hot CH3OH and Et2O and dried under vacuum.
As pointed out, in the case of the Ru(II) complexes 2a, 2b and 2c
with various substituted 1,10-phenanthrolines, the strong increase
of the second-order NLO response is characterized by the presence
of a rather strong absorption band in the range 459–507 nm,
suggesting that this latter is a MLCT transition at relatively low
energy, thus producing a relevant effect on the second-order NLO
response. This suggestion is supported by the evidence that the
increase of the second-order NLO response moving from 2a to 2c
occurs with a parallel red shift of this band (Table 1). This new
band could be attributed to a significant red-shift of the dp → pp*
MLCT band involving the 1,10-phenanthroline p* system due to
the increased electronic density on the Ru(II) centre, produced
by coordination of two phosphines. However in complexes 5
and 6, with a fullerene substituent on the p* acceptor chelated
ligand, there is always a band at about 480 nm, independent of
whether the two phosphines are present, although when they are
present these latter ligands increase the intensity of this band about
4–5 times (Table 1). A TD-DFT investigation is underway to give
a definite answer to the electronic origin of the second-order NLO
response in these interesting Ru(II) NLO chromophores.
Yield: 43%. 1H-NMR (400 MHz, CDCl3, 25 ◦C, TMS): d (ppm)
9.96 (d, 2H), 9.02 (d, 2H), 8.39 (s, 2H), 8.20 (m, 2H). IR(CHCl3),
nCO (cm-1): 2069, 2011. Anal. calcd (found) for RuC14H8N2O2Cl2:
C 41.20 (41.33), H 1.97 (1.98), N 6.86 (6.82).
Trans-Cl,cis-CO-[Ru(5-NO2-1,10-phen)(CO)2Cl2] (1b). Yield:
47%. H-NMR (400 MHz, CDCl3, 25 ◦C, TMS): d (ppm) 9.69
1
(dd, 1H), 9.68 (dd, 1H), 9.45 (dd, 1H), 9.02 (s, 1H), 8.82 (dd, 1H),
8.18 (m, 2H). IR(CHCl3), nCO (cm-1): 2072, 2014. Anal. calcd
(found) for RuC14H7N3O4Cl2: C 37.11 (37.01), H 1.55 (1.56), N
9.27 (9.24).
Cis-Cl,trans-PPh3-[Ru(1,10-phen)(PPh3)2Cl2]
(2a). [Ru-
(PPh3)3Cl2] (328 mg, 0.34 mmol) and the 1,10-phenanthroline
ligand (62 mg, 0.34 mmol) were dissolved in 20 mL of degassed
CH2Cl2 and the mixture was heated under reflux. After 2 h the
dark-red solution became cloudy and a brown powder appeared.
The solid was filtered, washed with hot CH3OH and Et2O and
dried under vacuum.
Yield: 56%. 1H-NMR (400 MHz, CD2Cl2, 25 ◦C, TMS): d (ppm)
8.90 (d, 2H), 7.79 (d, 2H), 7.74 (s, 2H), 7.31 (t, 12H), 7.15 (t,
6H), 7.02 (m, 12H), 6.86 (dd, 2H). 31P-NMR (CD2Cl2, 25 ◦C,
TMS): d (ppm) 24.36 (s, 2P, trans-PPh3). Anal. calcd (found) for
RuP2C48H38N2Cl2: C, 65.75 (65.90): H 4.37 (4.37), N 3.20 (3.25).
Experimental
Synthesis and characterization of the various Ru(II) complexes
General information. All reagents and solvents were purchased
from Sigma–Aldrich.
Cis-Cl,trans-PPh3-[Ru(5-NO2-1,10-phen)(PPh3)2Cl2]
(2b).
Yield: 67%. 1H-NMR (400 MHz, CDCl3, 25 ◦C, TMS): d (ppm)
9.23 (d, 1H), 9.13 (d, 1H), 8.63 (s, 1H), 8.47 (d, 1H), 7.85 (d, 1H),
7.32 (m, 11H) 7.12 (t, 6H), 7.03 (m, 13H), 6.89 (m, 2H). 31P-NMR
(CDCl3, 25 ◦C, TMS): d (ppm) 23.08 (s, 2P, PPh3). Anal. calcd
(found) for RuP2C48H37N3O2Cl2: C 62.55 (62.48), H 4.05 (4.01),
N 4.56 (4.58).
1H and 31P NMR spectra were obtained on a Bruker Avance
DRX 400 MHz instrument. Elemental analyses were carried
out in the Dipartimento di Chimica Inorganica, Metallorganica
e Analitica “Lamberto Malatesta” of the Milan University.
Dipole moments, m, were measured in CHCl3 using a WTW-
DM01 dipole meter (dielectric constant) coupled with a RX-5000
ATAGO Digital Refractometer (refractive index) according to
the Guggenheim method.16 All reactions were carried out under
a nitrogen atmosphere. [Ru(CO)2Cl2]n and [Ru(PPh3)3Cl2] were
prepared as described in the literature.9,10
Cis-Cl,trans-PPh3-[Ru(4,7-diphenyl-1,10-phen)(PPh3)2Cl2] (2c).
Yield: 67%. 1H-NMR (400 MHz, CDCl3, 25 ◦C, TMS): d (ppm)
8.99 (d, 2H), 7.78 (s, 2H), 7.67 (m, 6H), 7.39 (m, 16H), 7.12 (m,
6H), 7.02 (m, 12H) 6.75 (sbr, 2H), 1.57 (s, 2H). 31P-NMR (CDCl3,
25 ◦C, TMS): d (ppm) 23.50 (s, 2P, PPh3). Anal. calcd (found) for
RuC60H46N2P2Cl2: C 70.03 (69.97), H 4.50 (4.55), N 2.72 (2.69).
The known complexes trans-Cl,cis-CO-[Ru(1,10-phen)(CO)2-
Cl2] (1a) and cis-Cl,trans-PPh3-[Ru(1,10-phen)(PPh3)2Cl2)] (2a)
were also prepared as previously reported.8,9 The new complex
trans-Cl,cis-CO-[Ru(5-NO2-1,10-phen)(CO)2Cl2)] (1b) was pre-
pared with the same procedure as described below in the case
of 1a, whereas the complexes cis-Cl,trans-PPh3-[Ru(5-NO2-1,10-
phen)(PPh3)2Cl2)] (2b) and cis-Cl,trans-PPh3-[Ru(4,7-diphenyl-
1,10-phen)(PPh3)2Cl2] (2c) were prepared as described in the case
of 2a.10,11
The new complexes trans-Cl,cis-CO-[Ru(4,5-diaz)(CO)2Cl2] (3,
diaz = diazafluorene), cis-Cl,trans-PPh3-[Ru(4,5-diaz)(PPh3)2Cl2]
(4), trans-Cl,cis-CO-[Ru(9-fulleriden-4,5-diaz)(CO)2Cl2] (5) and
cis-Cl,trans-PPh3-[Ru(9-fulleriden-4,5-diaz)(PPh3)2Cl2] (6) were
prepared similarly using 4,5-diazafluorene12 or 9-fulleriden-4,5-
diazafluorene13 instead of the 1,10-phenanthroline derivatives. The
geometry of the complexes was given on the basis of IR and NMR
spectroscopies, according to the literature.14
Trans-Cl,cis-CO-[Ru(4,5-diaz)(CO)2Cl2] (3). The polymeric
precursor [Ru(CO)2Cl2]n (0.36 mmol, 80 mg) was dissolved in hot
degassed CH3OH (20 mL) under nitrogen, affording a pale yellow
solution that was cooled to room temperature. Then the ligand
(0.36 mmol, 61 mg) was slowly added. The colour of the solution
changed from light yellow to dark yellow. The solution was heated
under stirring for 2 h. Then the resultant yellow precipitate was
filtered under nitrogen, washed with CH3OH and hexane and dried
under vacuum.
Yield: 53%. 1H-NMR (400 MHz, CDCl3, 25 ◦C, TMS): d
(ppm) 8.90 (d, 2H), 8.16 (d, 2H), 7.65 (dd, 2H), 4.37 (s, 2H).
13C-NMR (400 MHz, CDCl3, 25 ◦C): d (ppm) 195.179 (s, 2C,
CO). IR(CHCl3), nCO (cm-1): 2069, 2006. Anal. calcd (found) for
RuC13H8N2O2Cl2: C 39.41 (39.37), H 2.03 (2.01), N 7.07 (7.04).
10316 | Dalton Trans., 2010, 39, 10314–10318
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Cis-Cl,trans-PPh3-[Ru(4,5-diaz)(PPh3)2Cl2] (4). Yield: 57%.
1H-NMR (400 MHz, CDCl3, 25 ◦C, TMS): d (ppm) 8.80 (d, 2H),
7.84 (d, 2H), 7.55 (dd, 2H), 7.14 (m, 12H), 7.06 (m, 6H), 6.89 (m,
12H), 4.07 (s, 2H). 31P-NMR (CDCl3, 25 ◦C, TMS): d (ppm) 22.57
(s, 2P, PPh3). Anal. calcd (found) for RuC47H38N2P2Cl2: C 65.28
(65.21), H 4.40 (4.38), N 3.24 (3.22).
Raman-shifting the fundamental 1.064 mm wavelength produced
by a Q-switched, mode-locked Nd3+:YAG laser manufactured
by Atalaser. The apparatus for the EFISH measurements was a
prototype made by SOPRA (France). The mbEFISH values reported
are the mean values of 16 successive measurements performed on
the same sample.
X-Ray determination of the structure of Cis-Cl,trans-PPh3-
[Ru(5-NO2-1,10-phen)(PPh3)2Cl2] (2b)†. Crystals of Cis-
Cl,trans-PPh3-[Ru(5-NO2-1,10-phen)(PPh3)2Cl2], suitable for
single-crystal X-ray diffraction studies, were obtained by slow
addition at room temperature of pentane to a solution of the
complex in CH2Cl2.
Trans-Cl,cis-CO-[Ru(9-fulleriden-4,5-diaz)(CO)2Cl2] (5). The
polymeric precursor [Ru(CO)2Cl2]n (0.086 mmol, 20 mg) was
dissolved in hot degassed MeOH (6 mL). The pale yellow solution
was cooled at room temperature. The ligand (0.086 mmol, 76 mg)
was dissolved in a mixture of cold degassed CS2 (10 mL) and
CH2Cl2 (3 mL) in a Schlenk tube, affording a dark red solution
that was added via cannula to the first one. The resultant solution,
cloudy and red, was heated under reflux for 48 h affording a
brown precipitate that was filtered under nitrogen and dried under
vacuum.
Crystal data for 2b. C48H37Cl2N3O2P2Ru, M = 921.72, mono-
◦
˚
clinic, a = 15.502(3), b = 17.677(4), c = 15.861(3) A, b = 105.97(3) ,
3
˚
U = 4178.6(16) A , T = 294(2) K, space group P21/n (no. 14), Z =
4, m = (Mo-Ka) 0.624 mm-1. 33 525 reflections (10 548 unique;
Rint = 0.049) were collected at room temperature in the range 1.84
<2q <58.32◦, employing a 0.12 ¥ 0.07 ¥ 0.05 mm crystal mounted
on a Bruker APEX II CCD diffractometer and using graphite-
Yield: 46%. 1H-NMR (400 MHz, CDCl3 + CS2, 25 ◦C, TMS): d
(ppm) 9.19 (m, 2H), 7.86 (m, 1H). IR(CHCl3), nCO (cm-1): 2062,
1989. Anal. calcd (found) for RuC73H6N2O2Cl2: C 78.65 (78.44),
H 0.54 (0.53), N 2.51 (2.49).
˚
monochromatized Mo-Ka radiation (l = 0.71073 A). Final R1
[wR2] values are 0.0455 [0.2222] on I > 2s(I) [all data].
Cis-Cl,trans-PPh3 -[Ru(9-fulleriden-4,5-diazafluorene)(PPh3)2-
Cl2] (6). The precursor [Ru(PPh3)3Cl2] (0.043 mmol, 41 mg)
and the ligand (0.043 mmol, 38 mg) were dissolved under
nitrogen in degassed CS2 (10 mL). The dark red solution was
heated under reflux. The reaction was monitored by Thin Layer
Chromatography (Silica; toluene : MeOH = 9 : 1). After 18 h,
the solvent was removed under vacuum and a sticky solid was
formed. This precipitate was dissolved in CH2Cl2, filtered, dried
and ground in Et2O in order to obtain a dark brown powder. This
powder was filtered using a Bu¨chner funnel, dried under vacuum
and further purified by column chromatography (silica gel).
Yield: 48%. 1H-NMR (300 MHz, CDCl3, 25 ◦C, TMS): d (ppm)
8.21 (d, 2H), 7.70 (m, 20H), 7.67 (m, 6H), 7.35 (d, 2H), 7.17 (m,
14H), 6.77 (t, 2H), 5.31 (s, 2H). 31P-NMR (400 MHz, CDCl3,
25 ◦C): d (ppm) 24.171 (s, 2P, PPh3). Anal. calcd (found) for
RuC107H36N2P2Cl2: C 81.16 (80.95), H 2.29 (2.30), N 1.77 (1.76).
Datasets were corrected for Lorentz-polarization effects and
for absorption (SADABS17). The structure was solved by direct
methods (SIR-9718) and completed by iterative cycles of full-
matrix least squares refinement on Fo2 and DF synthesis using the
SHELXL-9719 program (WinGX suite)20 Hydrogen atoms, located
on the DF maps, were allowed to ride on their carbon atoms.
Conclusions
In conclusion, we have shown that various Ru(II) complexes with
substituted 1,10- phenanthroline or 4,5- diazafluorene represent
a new interesting family of highly active second-order NLO
chromophores. Remarkably, the presence of a fullerene substituent
produces a strong enhancement of the second-order NLO re-
sponse, but maintaining a significant transparency towards the
second harmonic generation, as for instance in the case of 5
and 6. These properties make them excellent candidates for the
preparation of materials characterized by high second harmonic
generation properties, potentially also redox-switchable due to the
presence of Ru(II).
Second-order NLO properties: EFISH measurements
The molecular quadratic hyperpolarizabilities of all of the inves-
tigated complexes (Table 1) were measured by the solution-phase
dc Electric Field Induced Second Harmonic (EFISH) generation
method,4 which can provide direct information on the intrinsic
molecular NLO properties through eqn (1):
Acknowledgements
We thank MIUR (FIRB 2004: RBPR05JH2P) and Fondazione
CARIPLO (2008) for support.
g EFISH = (mbl/5kT) + g (-2w; w, w, 0)
(1)
where mbl/5kT is the dipolar orientational contribution and
g (-2w; w, w, 0), a third order term corresponding to the mixing
of two optical fields at w and of the DC poling field at w = 0, is the
electronic cubic contribution to g EFISH which is usually negligible.
bl is the projection along the dipole moment axis of the vectorial
component of the tensor of the quadratic hyperpolarizability,
working with an incident wavelength l.
All EFISH measurements were carried out at the Dipartimento
di Chimica Inorganica Metallorganica e Analitica “Lamberto
Malatesta” of the Universita` degli Studi di Milano, in DMF
solutions at a concentration of 1 ¥ 10-3 M, working with a
non resonant incident wavelength of 1.907 mm, obtained by
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10318 | Dalton Trans., 2010, 39, 10314–10318
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