A novel Ru(II) complex composed of Ruthenium and 3 ligands has been successfully synthesized. The ligands are firstly synthesized ; the ligand 1,10-phenanthroline-5-carboxylic acid (compound D) acts as an anchor for connecting with different compound (for example, connecting with the quantum dots) whereas the 2 other ligands  (compound H)  playing important role for linear and non-linear optical properties. Secondly, these ligands (compound H, compound D) are attached to initiator Ru salt, respectively. Optical properties of this novel Ru(II) complex were investigated via absorption, luminescent measurements. Additionally, I also used theoritical calculation TDDFT (time dependent density functional theory) to display frontier molecular orbitals of ligands for linear and non-linear optical properties, to assign electronic transitions in absorption spectra of complex. Significant result is luminescence intensity dependent on the dioxygen concentration, ascribed to the luminescence from 3MLCT state, centered at 600 nm. Energy transfer between 3MLCT state and the fundamental triplet state of dioxygen can be studied in order to evaluate the photosensitizing ablities of the complex. This complex can also be used as oxygen concentration sensor at a given temperature. Keywords. Ru(II) complex, ligands, anchor, luminescence, quantum dot

Vuong, Bui Xuan

English

Vietnam Academy of Science and Technology: Journals Online

 Vietnam Journal of Chemistry, International Edition, 55(2): 222-226, 2017 
DOI: 10.15625/2525-2321.2017-00448 
222 
 
 
 
Study on optical properties of novel Ru(II) complex 
Bui Xuan Vuong
1,2 
1Ho Chi Minh City Industry and Trade College 
2Ton Duc Thang University 
Received 31 October 2016; Accepted for publication 11 April 2017 
 
Abstract  
A novel Ru(II) complex composed of Ruthenium and 3 ligands has been successfully synthesized. The ligands are 
firstly synthesized ; the ligand 1,10-phenanthroline-5-carboxylic acid (compound D) acts as an anchor for connecting 
with different compound (for example, connecting with the quantum dots) whereas the 2 other ligands  (compound H)  
playing important role for linear and non-linear optical properties. Secondly, these ligands (compound H, compound D) 
are attached to initiator Ru salt, respectively. Optical properties of this novel Ru(II) complex were investigated via 
absorption, luminescent measurements. Additionally, I also used theoritical calculation TDDFT (time dependent density 
functional theory) to display frontier molecular orbitals of ligands for linear and non-linear optical properties, to assign 
electronic transitions in absorption spectra of complex. Significant result is luminescence intensity dependent on the 
dioxygen concentration, ascribed to the luminescence from 3MLCT state, centered at 600 nm. Energy transfer between 
3MLCT state and the fundamental triplet state of dioxygen can be studied in order to evaluate the photosensitizing 
ablities of the complex. This complex can also be used as oxygen concentration sensor at a given temperature.  
Keywords. Ru(II) complex, ligands, anchor, luminescence, quantum dot. 
 
1. INTRODUCTION 
 
Coordination complexes own many advantages 
such as synthetic tailorability, the possibility of long 
luminescence lifetime of the MLCT (metal-to-ligand 
charge transfer) triplet excited state (a few 
microseconds are generally obtained for Ru(II) 
complexes for example) [1]. The access via TPA 
(two-photon absorption) to 3MLCT can generate 
interesting luminescence properties (also based on 
effects two-photon excited fluorescence TPEF) for 
applications in biological imaging, O2 sensor [1] and 
optical power limited in the near infrared range [2, 
3].  
 According to the nature of ít coordination 
sphere, ruthenium has several oxidation states: 
Ru(II), Ru(III), and Ru(IV). Most of these oxidation 
states are accessible under physiological conditions.  
 Among ruthenium complexes, ruthenium(II) 
complexes are still the most attractive for scientific 
researchers. They have indisputable advantages, for 
a wide range of applications such as optical power 
limiting [4-6], optical data processing, biological 
imaging [7], photosensitizers (PS) in the conversion 
of solar energy [8], and PS for application in 
photodynamic therapy (PDT) [9-11]. For example, 
ruthenium(II) complexes containing a benzimidazole 
ligand have important applications in optoelectronic 
devices, and efficient sensitizers for molecular 
photovoltaics [12]. A series of Ru(II) complexes of 
polyphosphine ligands has been used as catalyst 
precursors in the homogeneous hydrogenation of 
cyclohexene, cyclohexanone, propanal and 2-
cyclohexen-1-one [13]. These polyphosphine Ru(II) 
complexes show enhanced catalytic activities in 
comparison with monodentate or bidentate 
phosphine or arsine analog.  From another point of 
view, tetraamine-based ruthenium(III) and (II) 
complexes constitute very interesting class of 
compounds for medicinal chemistry studies because 
of their water solubility, stability in an aqueous 
medium, and low cytotoxicity [3]. Furthermore, 
ruthenium(II) complexes possess many interesting 
properties such as luminescent property and high 
stability with a large number of potential ligands [6], 
allowing their use in practical applications. 
This study was focused on the synthesis of a 
novel Ru(II) complex (Fig. 1). This is heteroleptic 
Ru(II) complex involving three bidentate ligands: 
two ligands (L) playing an important role for linear 
and nonlinear optical properties and a third ligand 
such as an anchor (A) for connecting with the 
quantum dots. The optical properties of this novel 
Ru(II) complex were also examined. 
 VJC, 55(2), 2017  Bui Xuan Vuong 
 223 
 
Figure 1: Molecular structure of novel Ru(II) 
complex 
 
2. MATERIALS AND METHODS 
 
2.1. Materials 
 
Main chemical reagents used are Javel water 
Lacroix; 1,10-phenanthroline monohydrate, Sigma-
Aldrich, ≥ 99 %;  Potassium cyanide, Sigma-
Aldrich, ≥ 96 %; Potassium hydroxide, Sigma-
Aldrich, ≥ 90 %; Bromohexane, Sigma-Aldrich, ≥ 
98 %;           n-Butyllithium solution 2.5 M in 
hexane, Sigma-Aldrich; Triisopropyl borate, Sigma-
Aldrich, ≥ 98 %; 2-bromofluorene, Sigma-Aldrich, 
95 %; RuCl2(DMSO)4, Sigma-Aldrich, 98 %; 5-
bromo-1,10-phenanthroline, Sigma-Aldrich, 99 %. 
 
2.2. Synthesis 
 
2.2.1. Synthesis of the ligands 
 
2.2.1.1. Synthesis of the anchor 
 
Using Javel water (NaClO and NaCl aqueous 
solution) as a strong oxidant in order to react with 
1,10-phenanthroline monohydrate while controlling 
the pH, temperature under vigorous agitation, the 
compound 5,6-epoxy-5,6-dihydro-1,10-
phenanthroline have been obtained as a hygroscopic 
solid (see Scheme 1, reaction 1). 
 
 
Scheme 1: Synthesis of the Phen-COOH ligand 
 
Using potassium cyanide KCN 1M as a 
nucleophilic reagent in a common class of epoxy 
ring opening reaction, the compound 5-cyano-1,10-
phenanthroline was obtained as a white powder (see 
Scheme 1, reaction 2).  
Using potassium hydroxide KOH 6 M and 
adjusting the pH around 5.4, the expected compound 
(Phen-COO-) was collected as a powder (see 
Scheme 1, reaction 3). 
 
2.2.1.2. Synthesis of the two-photon antenna ligands 
 
We use bromohexane for Friedel-Crafts 
alkylation, controlling the reaction at room 
temperature (RT) for 2 hours and at 60 oC for 2 
hours. After obtaining a crude compound, we 
purified the product by chromatographic technique 
(Silica gel column, eluent: n-hexane). The 
compound 2-bromo-9,9-dihexylfluorene was 
obtained as liquid product (see Scheme 2, reaction 
4). 
 
Scheme 2: Synthesis of [5-(9,9-dihexylfluoren-2-
yl)]-phenanthroline (R = C6H13) 
 
Using lithium anion trapping and controlling the 
reaction at low temperature (-78 oC), we obtained 
the crude product. After that, using the 
chromatographic technique (silica gel column, 
eluent: dichloromethane, a mixture of solvents) to 
purify, the pure product of 2-(9,9-dihexylfluorenyl) 
boronic acid was obtained as a white solid (see 
Scheme 2, reaction 5). 
Aryl halide and aryl boronic acid was used as 
reagents for Suzuki reaction. Pd (0) was added as a 
catalyst. The reaction was kept under reflux system 
and vigorous agitation for three days. After 
collecting crude compound, continuing to purify by 
chromatographic technique (alumina column, 
mixture eluents of dichloromethane 80 %, acetone 
19 %, triethylamine 1 %), ligand L1 was obtained as 
a white solid (see Scheme 2, reaction 6).  
 
2.2.2. Synthesis of the ruthenium complex 
 
Related ruthenium complex RuCl2(L1)2 (see 
Scheme 3, reaction 7) was obtained by reaction 
under reflux of 2 equivalents of ligand L1 (in 
ethanol) with 1 equivalent of ruthenium dichloride 
tetra(dimethylsulfoxide) (in ethanol) and 
precipitated in dichloromethane.  
Novel ruthenium complex (see Scheme 3, 
reaction 8) is synthesized by reaction under reflux of 
 VJC, 55(2), 2017  Study on optical properties of… 
 224 
one equivalent of RuCl2(L1)2 with 1 equivalent of 
1,10-phenanthroline-5-carboxylic acid and 
precipitated by ammonium hexafluorophosphate 
(NH4PF6). 
 
Scheme 3: Synthesis of the ruthenium(II)  
complex (J) 
 
2.3. Instrument and characteristics 
 
UV-Vis absorption spectra were recorded in the 
200-800 nm range on a Shimadzu spectro-
photometer, with λmax given in nm and molar 
extinction coefficients ε in L.mol-1.cm-1; Fluorescent 
spectra were acquired by a Varian 
spectrofluorimeter. 
 
3. RESULTS AND DISCUSSION 
 
All synthetic compounds were checked by 1H 
NMR spectra on a Bruker 250 MHz spectrometer or 
elemental analysis on AAS spectrometer. This paper 
reports the obtained results concerning two optical 
charactetic methods. 
 
3.1. Absorption spectra of the Ru(II) complex (J) 
 
The absorption spectrum of compound J in 
CH3CN is reported in figure 2. It is composed of (a) 
a broadband in the 400-600 nm range (  around 
20000 L mol-1 cm-1), which corresponds to 
d (Ru(II)) *-metal-to-ligand charge transfer 
(MLCT) transitions and which is characteristic of 
this kind of Ru(II) complexes involving 
polypyridyle ligands, (b) a broad and intense band 
around 320 nm (  around 30000 L mol-1 cm-1), 
which, may be due to an intra-ligand charge-transfer 
(ILCT) transition involving a charge flow from the 
fluorene unit (F) to the 1,10-phenanthroline moiety 
(P) of the P-F ligand. As shown here, this band is 
observed at nearly the same wavelengths for the free 
ligand ( max = 380 nm). In both cases, the large 
width of this absorption band can be mainly ascribed 
to the thermal and vibronic broadenings; (c) finally, 
the bands from 200 to 270 nm (  around 120000 L 
mol-1 cm-1), which may correspond to ILCT 
transitions of higher energies, but can also mainly 
ascribed to π-π* electronic transitions, centered on 
aromatic ring such as the 1,10-phenanthroline 
moiety and the fluorene unit.  
 
Figure 2: Absorption spectra of the PF ligand and 
the related ruthenium complex J 
 
The obtained results also corresponded to 
TDDFT (Time-dependent density functional theory) 
calculation (figure 3). 
  
 
Figure 3: Frontiers molecular orbitals of PF ligand 
(TDDFT calculations) 
 
3.2. Luminescence spectra of the Ru(II) complex 
(J) 
 
Luminescence was recorded for the Ru(II) 
complex in acetonitrile and at room temperature (see 
figure 4). The emission spectra observed for the 
complexes can be ascribed to the luminescence from 
the 3MLCT state, centered at 600 nm. The triplet 
character of the emissive excited state can be 
ε
(L
. 
m
o
l-
1
. 
c
m
-1
)
 
 VJC, 55(2), 2017  Bui Xuan Vuong 
 225 
evidenced by the dependence of the luminescence 
intensity on the O2 concentration (see figure 6 for 
the spectra at three different concentrations: air, O2, 
and Ar atmosphere). Energy transfer between the 
3MLCT state and the fundamental triplet state of the 
dioxygen can be studied in order to evaluate the 
photosensitizing abilities of these complexes. 
 
 
Figure 4: Emission spectra (in acetonitrile) of Ru(II) 
complex (J) for 3 dioxygen concentrations 
 
 
Figure 5: Stern-Volmer oxygen quenching plot in 
solution of the Ru(II) complex (J) (slope 10.2 bar-1) 
in acetonitrile 
 
Actually, oxygen is a dynamic or collisional 
quencher of the complexes. In fluid solution, the 
dependence of emission intensity and lifetime with 
quencher concentration is given by the following 
Stern-Volmer equations: 
 
0 I0
I
1 KSV O2 1 kq 0 O2 1 kq 0KH
solvP
O2
 (1) 
where the s parameters are emission intensities, the 
s are lifetimes, KSV is the linear Stern-Volmer 
quenching constant, kq is the bimolecular rate 
constant for quenching of the excited state; and K
H
solv
 
is the Henry constant of O2 (gas) in the particular 
solvent; [O2] is the O2 concentration in this solvent. 
The subscript 0 denotes the values of the quantity in 
the absence of the quencher. Plots of I0/I and 0/  
versus oxygen concentration will be linear with 
identical slopes equal to KSV if there is a single class 
of luminophores that are all equally accessible to the 
quencher. The luminescence quenching curves (I0/I 
representations) for the J compound is shown in 
figure 5. The Stern-Volmer slopes in O2(g) partial 
pressure illustrate that the quenching was in good 
agreement with the linear Stern-Volmer equation. 
The KSV value was found around 10 bar
-1. 
 
4. CONCLUSION 
 
A new Ru(II) complex containing 2 antena 
ligands and one anchor ligand has been obtained 
with interesting luminescent property. The obtained 
results indicated that this novel Ru(II) complex is 
very sensitive to dioxygen concentration, as the 
result of efficient 3MLCT from the triplet excited Ru 
complex to the fundamental triplet state of the 
dioxygen. The energy transfer can be studied in 
order to evaluate the photosensitizing ability. This 
complex is potential  as a dioxygen concentration 
sensor at a given temperature. Additionaly, with an 
anchor ligand, it can easily connect with some other 
specific compounds, for example, functionalize with 
quantum dot for bio-imaging apllications.  
 
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Corresponding author: Vuong Xuan Bui 
Ton Duc Thang University 
98 Ngo Tat To Str., Ward 19, Binh Thanh District, Ho Chi Minh City or 
HCM City Industry and Trade College 
63 Ung Van Khiem, Binh Thanh District, Ho Chi Minh City 
E-mail: buixuanvuong@tdt.edu.vn; Telephone number: 01276517788. 
 


Study on optical properties of novel Ru(II) complex

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Study on optical properties of novel Ru(II) complex

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