Orange Fluorescent Ru(III) Complexes Based on 4′-Aryl Substituted 2,2′:6′,2″-Terpyridine for OLEDs Application

Article abstract of DOI:10.1007/s10895-017-2180-5

A series of ruthenium (III) complexes of the formulae [Ru(4-Mephtpy)₂]Cl₃(1) [Ru(L₁)], [Ru(3,4,5-tmphtpy)₂]Cl₃(2) [Ru(L₂)], and [Ru(4-thptpy)₂]Cl₃(3) [Ru(L₃

Full text of DOI:10.1007/s10895-017-2180-5

J Fluoresc
DOI 10.1007/s10895-017-2180-5
ORIGINAL ARTICLE
Orange Fluorescent Ru(III) Complexes Based on 4′-Aryl
Substituted 2,2′:6′,2″-Terpyridine for OLEDs Application
Raja Lakshmanan1 · N. C. Shivaprakash2 · S. Sindhu1
Received: 14 August 2017 / Accepted: 19 September 2017
© Springer Science+Business Media, LLC 2017
Abstract A series of ruthenium (III) complexes of the
formulae [Ru(4-Mephtpy)2]Cl3(1) [Ru(L1)], [Ru(3,4,5-
tmphtpy)2]Cl3(2) [Ru(L2)], and [Ru(4-thptpy)2]Cl3(3)
[Ru(L3)], (where L=terpy=2.2′:6′2″ terpyridine ligands)
are synthesized. The complexes were characterized by ele-
mental analyses, spectroscopic and electrochemical data.
The density functional theory (DFT) outlines the geometric
optimisation and electronic charge transition of these com-
plexes. Photophysical studies describe that the luminescence
of Ru(III) complexes is due to electronic transition between
the energy levels of singly unoccupied molecular orbitals
(SUMO) and singly occupied molecular orbitals (SOMO). It
also exhibits the potential charge transfer to π–π* and n–π*
states due to MLCT and ILCT processes of the complexes.
The observed bands centered at 591 and 620 nm demonstrate
that these emissions originated from the transition of SUMO
to SOMO energy levels, that is, from the radiative decay
from the doublet exciton. Due to the heavy metal effect of
Ru(III) ions the photophysical behaviour depends on the
MLCT process. In conclusion, that the all three Ru(L1-L3)
complexes are fallen orange emission.
Introduction
Recently, organometallic complexes are used widely to syn-
thesize optoelectronic devices, such as organic solar cells
and for OLEDs [1–5]. Transition metal-based organometal-
lic complexes are of interest due to their versatile nature
like ease of tuning the photophysical, electrochemical and
magnetic properties [6–8]. These properties strongly depend
on the oxidation states of the transition metal used in the
complex. Among the various transition metals, ruthenium
has gained interest in the preparation of organometallic com-
plexes for OLED applications [9, 10]. Barthelmes et al. syn-
thesised ruthenium-based terpy metal complexes and stud-
ied their photophysical and electrochemical properties [11].
Other research groups studied these and the thermal prop-
erties of Ru(II)-based pyridine complexes [12–14]. Many
studies have been conducted on the synthesis and charac-
terization of Ru(II)-based terpy complexes for luminescent
applications [15, 16]. Kelch et al. studied the spectroscopic
and electrochemical behaviour of rod-like ruthenium (II)
coordination polymers [17] and observed deep orange emis-
sions, strongly dependent on the nature of π-conjugated
bis-terpy ligands. The spectroscopic and electrochemical
properties of self-assembled metallo-polymers containing
electron-donating and electron-withdrawing Ru(III)-based
bis-terpy derivatives are still not clear [18, 19].
Keywords Photophysical properties · Ru(III) complexes ·
Orange fluorescent emitter · 2,2′:6′,2″ -terpyridine · OLEDs
The luminescence and redox properties of Ru(III) com-
plexes are of great interest among the researchers for their
range of fundamental and practical applications [20, 21]. Ru
(III)-based terpy complexes exhibit a strong orange emission
with a suitable solvent. These emission bands could be due
to the MLCT process of the complexes [22, 23]. The white
light can be generated by mixing orange and blue emitters
[24]. Heteroleptic ruthenium complexes have more advan-
tages as functions of different groups can be integrated into
* S. Sindhu
sindhunair@pilani.bits-pilani.ac.in
1
Department of Physics, Birla Institute of Technology
and Science, Pilani, Rajasthan 333031, India
2
Department of Instrumentation and Applied Physics, Indian
Institute of Science, Bangalore 560012, India
Vol.:(0123456789)
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one molecule. Such complexes usually consist of two ligands
with easily substituting functional groups. It has been
observed that the functional groups in the ligand introduce
interesting photophysical and electrochemical properties
to the complexes [25, 26]. Researchers found that fluorine
substitutions into the ligand can lower the HOMO energy
level [27].
0.32 g; 3,4,5-tmphtpy, 0.35 g; 1.0 mmol, 4-thptpy, 0.28 g;
1.0 mmol) with stirring. The reaction mixture was refluxed
for 6 h to obtain a crystalline solid of the precursor complex,
which was filtered, washed with ice-cold ethanol followed by
diethyl ether and finally dried in a vacuum. Scheme 1 shows
synthetic route of (RuL1-L3) complexes.
Phosphorescence is frequently detected in Ru(III) com-
plexes at room temperature, which is attributed to the low-
lying MLCT excited states. It has both ligand-centered (LC)
and MLCT charge transition process [28, 29]. Extensive
work has been carried out on dinuclear Ru(II) homo- and
hetero-metallic complexes. In these complexes, the two
metal centers are connected by an organic wire type bridge.
The Ru(II)-based terpy complexes exhibit phosphorescence
behaviour in a few microseconds, whereas Ru(III)-based
terpy complexes exhibit similar characteristics in about a
few nanoseconds [30, 31]. Hence, the photophysical and
electrochemical behaviour of Ru ion depend on the oxida-
tion states; it’s interesting to study the oxidation states of
Ru ion-based organometallic complexes [32, 33]. A lack of
interest in the photochemical behaviour of Ru(III) deriva-
tives arises from observations that although their lowest
excited states are luminescent in glasses at low tempera-
tures, they are essentially non-emissive and short-lived in
solution at ambient temperature. It is necessary to introduce
cyclo-metallated ligands to complexes for luminescence in
solution [34].
[Ru(4-Mephtpy)2]Cl3: [Ru(L1)]
Yield: 67%, Tm. 425 °C, Anal. Calcd for C44H34Cl3N6Ru: C,
61.87; H, 4.01; N, 9.84. Found: C, 61.69; H, 4.07; N, 9.87.
IR (KBr): ν=3379 (w), 3308 (w), 3075 (w), 1586 (m), 1508
(m), 1461 (m), 1397 (m), 1306 (m), 1124 (w), 984 (s), 833
(m), 786 (m), 715 (s), 742 (w), 732 (s), 682 (m), 658 (m),
620 (m) cm−1. MS (ESI, m/z): 784.18 [M-3Cl]+.
[Ru(3,4,5-tmphtpy)2]Cl3: [Ru(L2)]
Yield: 74%, Tm. 429 °C, Anal. Calcd for C48H42Cl3N6O6Ru:
C, 57.29; H, 4.21; N, 8.35. Found: C, 57.31; H, 4.23; N,
8.37. IR (KBr): ν=3379 (w), 3307 (w), 1586 (m), 1508 (m),
1397 (m), 1351 (m), 1308 (w), 1162 (s), 1124 (m), 884 (m),
833 (s), 786 (w), 715 (s), 647 (m) cm− 1. MS (ESI, m/z):
899.94 [M-3Cl]+
[Ru(4-thptpy)2]Cl3: [Ru(L3)]
Yield: 68%, Tm. 471 °C, Anal. Calcd for C38H26Cl3N6SRu:
C, 56.62; H, 3.25; N, 10.42; S, 3.98. Found: C, 56.69; H,
3.28; N, 10.47; S, 3.97. IR (KBr): ν=3467 (w), 3056 (w),
3075 (w), 1595 (m), 1527 (m), 1414 (m), 1419 (m), 1359
(m), 1237 (w), 838 (s), 780 (s), 716 (s), 626 (m), 658 (m)
cm−1. MS (ESI, m/z): 699.81 [M-3Cl]+.
In this work, the synthesis of a series of three new orange-
fluorescent Ru(III)-based terpyridine complexes and their
characteristics like photophysical, thermal and electrochemi-
cal for fluorescent OLED applications are discussed. The
introduction of electron-donor substituents onto a terpy
ligand results in fluorescent emission at room temperature in
Ru(III) complexes. These are reflected in the electrochemical
properties with the electron-releasing substituents stabilizing
the Ru(III) state and lowering the potential of the Ru(II)/
Ru(III) couples.
Quantum Calculation of Ru(L1-L3) Complexes
Geometric optimization and electronic structure of the
Ru(L1-L3) complexes were achieved by DFT using a
B3LYP/def2-TZvP basis set employing Gaussion-09 pro-
gram [36]. In addition, energy levels of the frontier molecu-
lar orbitals (i.e., HOMO, SOMO, SUMO, and LUMO) of
three Ru(III) complexes were also obtained. The FMOs
along with individual contributions of Ru(III) complexes
were fully optimized as shown in Fig. 1. FMOs have two
types of charge transitions in the complexes MLCT and
ILCT. MLCT can be attributed to charge transition between
SOMO and SUMO energy levels of Ru ion. In ILCT, the
charge transition takes place between SOMO/HOMO and
the higher energy orbitals. This is mainly attributed to π–π*
and n–π* of terpyridine ligands [37, 38].
Experimental
Syntheses of Ru(III) Complexes (RuL1-L3)
The synthesis of terpyridine ligands, such as C1 and C2, was
published elsewhere [35]. Ligand C3 was also synthesised
using a procedure similar to that performed for ligands C1
and C2. The following sections provide the details of prepa-
ration of metal complexes.
The complexes were prepared following a general syn-
thetic route. An ethanolic solution (15 ml) of RuCl3·3H2O
(0.26 g, 1.0 mmol) was added dropwise to a dichlorometh-
ane solution (15 ml) of the terpyridine ligand (4-Mephtpy,
In all the complexes, the SOMO energy level is mostly
localized on the 4′-aryl substituent ring, whereas the
SUMO energy is localized between Ru ion and the terpy
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Scheme 1 Synthetic route of
Ru(III) terpyridine complexes
(RuL1-L3)
ring. Therefore, the electronic emission processes of all
complexes are mainly attributed to the Ru(III) ions, such
as transition from SUMO to SOMO, that is, the radiative
decay takes place from the doublet excitons. The orange
emission of the complexes is confirmed by PL spectra; the
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Fig. 1 Optimized geometry and electronic distribution of the frontier orbitals for Ru(III) terpy complexes (RuL1-L3)
molecular orbitals of Ru(III) are more stable as they are
located at lower energy levels.
Results and Discussion
UV–Vis Absorbance Spectra
The study of photophysical properties of Ru(III)-based
terpy complex is of great interest to researchers because
of their potential in optoelectronic applications. To inves-
tigate the influence of the electron-donating substituent
on terpy of Ru(III) complex, its photophysical properties,
such as UV–Vis absorption and PL spectra were evaluated.
Fig. 2 UV–Vis absorbance spectra of Ru(L1-L3) complexes in
The UV–Vis absorption spectra of Ru(L1-L3) complexes
DMSO
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in DMSO solution at room temperature are shown in
Fig. 2. All complexes exhibit high intense absorption bands
(250 − 350 nm) in UV region and less intense absorption
bands in the visible region (495–505 nm).
The former are due to π–π* and n–π* of LC charge tran-
sition of terpyridine ligands and the latter to spin-allowed
d–π* of MLCT transition process [39]. The shorter wave-
length bands of the spectra are attributed to transitions from
SOMO/HOMO to higher energy orbitals. Two maximum
absorption bands were observed for Ru(L1) and Ru(L2)
complexes, while one was observed for Ru(L3) complex
in the UV region of electromagnetic radiation. The maxi-
mum absorption peaks were observed at 275 and 308 nm for
Ru(L1), 280 and 310 nm for Ru(L2) and 290 nm for Ru(L3)
complexes (Table 1). The bathochromic shifts of the maxi-
mum absorbance of 5 and 10 nm are seen for Ru(L2) and
Ru(L3) complexes, respectively. The absence of second peak
as expected around 310 nm in Ru(L3) complex could be due
to the forbidden energy transition between Ru(III) and L3
ligand. In the absorption spectra, some bands are centered
at approximately 495, 500 and 505 nm for Ru(L1), Ru(L2)
and Ru(L3) complexes corresponding to the energy gap of
2.50, 2.48 and 2.46 eV, respectively, which are assigned to
the electronic transition from SOMO to SUMO. The less
intense and narrow absorption bands about 500 nm caused
orange emission of these complexes. These bands could be
due to d-d transition, which has been observed for similar
ruthenium (IV) complexes [31, 40, 41]. These charge transi-
tion bands also depict the 5 and 10 nm bathochromic shift
for Ru(L2) and Ru(L3) complexes, respectively. Hence, the
electron-donating substituents of 3,4,5-trimethoxyphenyl
and 4-thiophenyl group on terpy would have caused the red
shift of Ru(L2) and Ru(L3) complexes compared to Ru(L1)
complex. No significant bands were observed for the metal-
centered (MC) charge transition of all Ru(III) complexes.
Fig. 3 PL spectra of Ru(L1-L3) complexes recorded at excitation
wavelength of 310 nm for Ru(L1) and Ru(L2) complexes, whereas
290 nm for Ru(L3) complex in DMSO
show that the maximum emission bands are in the visible
region of the electromagnetic spectrum. The dilute solution
of Ru(III) complexes in DMSO shows a strong orange emis-
sion in the wavelength range starting from 591 to 620 nm.
These emission bands could be due to the MLCT process of
the complexes as confirmed by UV–Vis absorption spectra
[42]. The absorption maximum of the spin-allowed MLCT
band in the visible region for Os(terpy)2+ lies at the same
wavelength as that of Ru(terpy) [41, 43].
Further, the emission maximum band in the visible region
for Ru(L2) complex lies at the same wavelength as that of
Ru(L3) complex, but the emission maximum was observed
at 591 nm. This could be due to the more covalent charac-
teristic nature of the MLCT transition in the Ru(III) com-
plexes [44]. Since Ru(L2) and Ru(L3) complexes have the
same emission maximum bands it is believed that the same
MLCT contributed for these two complexes too. The maxi-
mum emission band was observed at 620 nm for Ru(L1)
complex, and the shoulder peak was at 620 nm for Ru(L2)
complex. All these transitions take place in the lower energy
transition from MLCT to the ground state [45]. In addition,
the Ru(L2) complex has the broadened emission spectrum
compared to Ru(L1) and Ru(L3) complexes in the visible
region. This broad emission of the Ru(L2) complex could
be due to the more electron-donating nature of the 3,4,5-tri-
methoxyphenyl substituent (to terpy ligand on Ru(III)). The
luminescence band of the Ru(L2) and Ru(L3) complexes
Photoluminescence Spectra
The PL spectra were recorded on excitation at 310 nm for
Ru(L1) and Ru(L2) complexes, while 290 nm for Ru(L3)
complex corresponds to the maximum absorption wave-
length of the complexes. The PL spectra of Ru(L1-L3) com-
plexes are shown in Fig. 3. A summary of photophysical data
of three complexes is presented in Table 1. The PL spectra
Table 1 Synthetic route of
Complexes
Absorption (λmax
)
Emission (λmax
)
Optical band Fluorescence
Melting
point
Ru(III) terpyridine complexes
(RuL1-L3)
gap (eV)
Lifetime (ns)
LC
MLCT
(°C)
Ru(L1)
Ru(L2)
Ru(L3)
275, 308
280, 310
290
459
500
505
620
591
591
2.50
2.48
2.46
0.27
0.46
0.52
425
429
471
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was considerably shifted to the blue by 29 nm compared to
Ru(L1) complex. Further, less-intense emission bands were
observed at 367, 406 and 500 nm for Ru(L1), Ru(L2) and
Ru(L3) complexes, respectively, probably due to charge tran-
sition between LC transitions of terpy ligands. The red shifts
are consistent with the LC charge transition of the UV–Vis
absorption maximum. The bands centering at approximately
591 and 620 nm demonstrate that the emissions originated
from the transition of SUMO to SOMO, that is, the radiative
decay from the doublet excitons.
couple is associated with successive reduction of Ru(II) to
Ru(I) (peaks CII→I at the potential of −0.40) and correspond
with the oxidation of Ru(I) to Ru(II) (peaks AI→II at the
potential of −0.22 V), respectively. The additional anodic
peak at AIII→IV observed at a potential of 1.08 V could be
attributed to the oxidation of Ru(III) to Ru(IV). This peak is
associated with a cathodic peak potential of 0.75 V, which
can be due to the reduction of Ru(IV) to Ru(III) [48].
Thermal Properties
Cyclic Voltammetry
The thermal properties of the three Ru(L1-L3) complexes
are characterised by TGA and DSC analysis. The Td, Tg and
Tm of these complexes were systematically studied. Figure 5
shows the DSC curves of the Ru(L1-L3) complexes under
nitrogen atmosphere, while the samples were heated up from
room temperature to slightly above their melting temperature
The redox properties of the Ru(L1-L3) complexes were stud-
ied by measurement with CV in a three-electrode cell sys-
tem. Tetrabutylammonium perchlorate (TBAP) (0.1 M) was
dissolved in acetonitrile (ACN) and used as an electrolyte
solution with ferrocene (Fc) as an internal standard. Figure 4
shows the cyclic voltammogram of the Ru(L1) complex in
the potential range between −1.4 and +2.0 V at a scan rate
of 100 mV s−1. The electrochemical properties of the Ru(III)
complexes are mainly dependent on the influence of Ru(III)
ions and not of terpy ligands [46]. Hence, the Ru(L1) com-
plex was considered to discuss the electrochemical prop-
erties of the Ru(III) complex. All three Ru(III) complexes
show a similar redox behaviour. The three redox couples
have been observed in the potential range of 1.1 to −0.4 V
for the Ru(L1) complex. The electrochemical data for the
three Ru(III) complexes is listed in Table 1. Further, it has
been noticed that the all complexes show a good reversible
redox process.
at a scanning rate of 10 °C min−1
.
It is observed that all the Ru(III) complexes have an
endothermic peak, which shows the melting point of the
complexes. The observed melting temperatures were 425,
429 and 471 °C for Ru(L1), Ru(L2) and Ru(L3) complexes,
respectively. The melting point of the Ru(L1) and Ru(L3)
complexes shows sharp endothermic peaks, whereas it is a
broad endothermic peak for the Ru(L2) complex. Among the
three Ru(III) complexes, Ru(L3) has a higher Tm than the
other two Ru(III) complexes, and hence, Ru(L3) complex
is thermally more stable [49]. The DSC thermograms of
Ru(III) complexes show no signature of Tg and crystalline
The cathodic peak CIII→II at a potential of 0.35 V and the
anodic peak AII→III at a potential of 0.55 V correspond to
the reduction of Ru(III) to Ru(II) and the oxidation of Ru(II)
to Ru(III), respectively [47]. Moreover, the second redox
Fig. 4 Cyclic voltammogram of Ru(L1) complex in acetonitrile (vs.
SCE). The process at about 0.25 V is due to ferrocene, added as a
reference
Fig. 5 DSC plots of the Ru(L1-L3) complexes
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Fig. 6 TGA thermogram of Ru(L1-L3) complexes
temperature (Tc). However, the thermogram of the Ru(III)
complexes shows a small inflection (exothermic peak) at a
low temperature, which could be due to the elimination of
volatile substrate. In conclusion, all the three complexes are
thermally very stable as well as crystalline. The observed
degradation temperatures are 202, 310 and 210 °C for
Ru(L1), Ru(L2) and Ru(L3) complexes, respectively (see
Fig. 6). Ru(L2) complex shows higher degradation tempera-
ture and thermal stability than the other two Ru(III) com-
plexes [50]. It is observed that no significant weight loss
takes place at low temperatures. Hence, these complexes
exhibit a good thermal stability with Td (thermal-decompo-
sition temperature at a wt.% of 95) in the range 250–313 °C.
The observed weight losses of 5% were 250, 313 and 297 °C
for the Ru(L1), Ru(L2) and Ru(L3) complexes, respectively.
The maximum rate of weight loss Td (thermal-decompo-
sition temperature at a wt% of 39%) takes place at 590 °C for
Ru(L2) complex. Moreover, around 70 wt% of the residue
composed of ruthenium ash and remained above 590 °C for
the Ru(L1) and Ru(L3) complexes. Compared to the free
ligand, the metal complexes revealed a significant increase in
thermal stability, as can be seen from the temperature onset
of a 5% weight loss [51]. Hence, Ru(III) complexes are more
stable on exposure to air and showed high thermal stability
in nitrogen atmosphere.
Fig. 7 Fluorescence decay spectra of Ru(L1) a, Ru(L2) b and Ru (L3)
c complexes at the excitation wavelength of 310 nm with one-expo-
nential fit residuals, χ2 =1.002
Figure 7 shows the fitted decay curve of Ru(L1-L3) com-
plexes in DMSO obtained by using the TCSPC method
under laser excitation at 310 nm with a 96.8 ps pulse width.
The luminescence decay spectra of the three complexes were
fitted by a single exponential decay function. The observed
lifetimes are 0.27, 0.46 and 0.52 ns for Ru(L1), Ru(L2) and
Ru(L3), respectively. Hence, the measured lifetime of the
Ru(L3) complex is significantly longer than the other two
Ru(III) complexes.
Fluorescence Lifetime Measurements
The lifetime of luminescence is an important parameter
as the luminescence property of a material depends on it.
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It has been reported that the longer conjugation length in
the ligand leads to longer lifetime [52]. The short-lived fluo-
rescence of Ru(L1) might be assigned to the strong intramo-
lecular coupling interaction of trimethoxy flurophores which
lead to the fast charge transfer process. The lifetime on the
nanosecond time scale indicates that the three Ru(III) com-
plexes have the fluorescent character of the luminescence.
Scanning Electron Microscope
The surface morphology of the synthesised Ru(L1-L3) com-
plexes was analysed by SEM as depicted in Fig. 8. Figure 8a
shows an SEM micrograph of the Ru(L1) complex, where
cauliflower-like structural particles have been observed. The
size of the particles ranges from 5 to 10 μm and the inset
shows a clear cauliflower-like structural particle of Ru(L1).
Figure 8b depicts the cauliflower-like structure along with
one-dimensional nano rod of the Ru(L2) complex with the
diameter ranging from 7 to 12 μm and the length being about
a few micrometers. Moreover, the SEM image of the Ru(L3)
complex, as shown in Fig. 8c shows one-dimensional micro-
rod structures with diameters of around 3 μm and about
7 μm length. The SEM images of the complexes reveal that
the Ru(L2) complex has more surface area and a greater
surface-to-volume ratio which could enhance the lumines-
cence properties [53].
Conclusion
In conclusion, three novel Ru(III) complexes were synthe-
sised and their photophysical, electrochemical and thermal
properties were studied by varying the electron-donating
substituents at the 4′-position of the 2,2′:6′,2″-terpyridine
ring. Spectral analysis showed that electroluminescence
of the OLED originated from electron transition between
SUMO and SOMO. These complexes exhibit high ther-
mal stability without any significant weight loss below
250 °C. All the complexes show good PL emissions in
a DMSO solution with a broad emission spectrum ca.
591–620 nm. The Ru(L2) complex exhibits a broad orange
emission compared to Ru(L1) and Ru(L3) complexes.
The measurements of the excited state lifetime confirm
that the potential charge transfer to the π–π* state of the
MLCT state in the complexes is efficient. The bands cen-
tered on 591 and 620 nm demonstrate that these emissions
originated from the transition of SUMO to SOMO, that
is, from radiative decay from the doublet exciton. These
observations imply that by simply changing the terminal
the substituent can lead to various optical properties, such
as deep orange emission for the three Ru(L1-L3) complex.
Although the devices using these complexes have not been
demonstrated in this work and are beyond the scope of the
Fig. 8 SEM images of a Ru(L1), b Ru(L2) and c Ru(L3) complexes
current discussion, it is believed that the OLEDs based on
them would exhibit a promising performance according to
the current results and have potential electron-transporting
properties from terpyridine derivatives.
Acknowledgements We thank the Council of Scientific and Indus-
trial Research (CSIR), Government of India for financial support. The
authors would like to acknowledge the Supercomputer Education and
Research Centre (SERC), Indian Institute of Science, Bangalore, India
for providing the computational facility.
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17. Kelch S, Rehahn M (1999) Rod-like ruthenium(II) coordination
polymers: synthesis and properties in solution. Chem Commun
0:1123–1124
References
1. Jou JH, Su YT, Hsiao MT, Yu HH, He ZK, Fu SC, Chiang
CH, Chen CT, Chou CH, Shyue JJ (2016) Solution-process-
feasible Deep-red phosphorescent emitter. J Phys Chem C
120:18794–11802
18. Wild A, Winter A, Schlutter F, Schubert US (2011) Advances in
the field of π-conjugated 2,2′:6′,2″-terpyridines. Chem Soc Rev
40:1459–1511
19. Rudmann H, Shimada S, Rubner MF (2002) Solid-state light-emit-
ting devices based on the tris-chelated ruthenium(II) complex.
4. high-efficiency light-Emitting devices based on derivatives of
the tris (2,2′-bipyridyl) ruthenium(II) complex. J Am Chem Soc
124:4918–4921
2. Nagai Y, Sasabe H, Takahashi J, Onuma N, Ito T, Ohisa S, Kido
J (2017) Highly efficient, deep-red organic light-emitting devices
using energy transfer from exciplexes. J Mater Chem C 5:527–530
3. Sun Y, Stephen RF (2008) Enhanced light out-coupling of organic
light-emitting devices using embedded low-index grids. Nat Pho-
ton 2:483–487
20. Chmielewski PJ, Latos-Grazynski L, Pacholska E (1994) Low-
valent nickel thiaporphyrins nuclear magnetic resonance and elec-
tron paramagnetic resonance studies. Inorg Chem 33:1992 – 1999
21. Latos-Grazynski L, Lisowski J, Olmstead MM, Balch AL (1989)
Five-coordinate complexes of 21-thiaporphyrin. Preparations,
spectra, and structures of iron (II), nickel (II), and copper (II)
complexes. Inorg Chem 28:3328 – 3331
4. Wood CD, Jone CW, Claverly JD, Blakesley JC, Giusca C, Castro
FA (2017) Transient photocurrent and photo voltage mapping for
characterisation of defects in organic photovoltaics. Sol Energ Mat
Sol Cells 161:89–95
5. Jayabharathi J, Ramanathan P, Karunakaran C, Thanikachalam
V (2016) Fused methoxynaphthyl phenanthrimidazole semicon-
ductors as functional layer in high efficient OLEDs. J Fluoresc
26:307–316
22. Umamahesh B, Karthikeyan NS, Sathiyanarayanan KI, Malicka
JM, Cocchi M (2016) Tetrazole iridium(III) complexes as a class
of phosphorescent emitters for high-efficiency OLEDs. J Mater
Chem C 4:10053–10060
6. Kim KH, Liao JL, Lee SW, Sim B, Moon C-K, Lee G-H, Kim HJ,
Chi Y, Kim J-J (2016) Crystal organic light-emitting diodes with
perfectly oriented non-doped Pt-based emitting layer. Adv Mater
28:2526–2532
23. Kusamoto T, Kume S, Nishihara H (2008) Realization of SOMO
– HOMO level conversion for a TEMPO-Dithiolate ligand by
coordination to platinum(II). J Am Chem Soc 130:13844 – 13845
24. Reineke S, Lindner F, Schwartz G, Schwartz G, Seidler N, Walzer
K, Lussem B, Leo K (2009) White organic light-emitting diodes
with fluorescent tube efficiency. Nature 459:234–238
7. Constable EC, Alexander MWCT, Armaroli N, Balzani V, Maes-
tri M (1992) Ligand substitution patterns control photophysical
properties of ruthenium(ii)-2,2′:6′,2″-terpyridine complexes-room
temperature emission from [ru(tpy)j2 + analogues. Polyhedron
11:2707–2709
25. De Silva AP, Gunaratne HQN, Gunnlaugsson T, Huxley AJM,
McCoy CP, Rademacher J, Rice TE (1997) Signaling recogni-
tion events with fluorescent sensors and switches. Chem Rev
97:1515–1565
8. Seino Y, Inomata S, Sasabe H, Pu YJ, Kido (2016) High-perfor-
mance green OLEDs using thermally activated delayed fluores-
cence with a power efficiency of over 100 lm W– 1. J Adv Mater
28:2638–2643
26. Vogtle F (1993) Supramolecular Chemistry. Wiley, Chichester
27. Kosaka W, Itoh M, Miyasaka H (2015) The effect of chlorine
and fluorine substitutions on tuning the ionization potential of
benzoate-bridged paddlewheel diruthenium(II, II) complexes.
Dalton Trans 44:8156–8168
9. Wang D, Xu QL, Zhang S, Li HY, Wang CC, Li TY, Jing YM,
Huang W, Zheng YX, Accorsi G (2013) Synthesis and photo-
luminescence properties of rhenium(I) complexes based on
2,2′:6′,2′′-terpyridine derivatives with hole-transporting units.
Dalton Trans 42:2716–2723
28. Mishra D, Naskar S, Butcher RJ, Chattopadhyay SK (2005)
Ruthenium(II/III) mediated transformation of 1,2-bis(2΄-
pyridylmethyleneimino) benzene (L) to 2-(2΄-benzimidazolyl)
pyridine (L′H) and its in situ formed complexes with Ru(II) :
10. Juris A, Balzani V, Barigelletti F, Campagna S, Belser P, Zelewsky
AV (1988) Ru(II) polypyridine complexes: photophysics, pho-
tochemwtry, electrochemistry, and chemiluminescence. Coord
Chem Rev 84:85–277
X-ray structure of trans-[Ru(PPh
3)2 (L′H)2](ClO4). Inorg Chim
Acta 358:3115–3121
11. Barthelmes K, Kubel J, Winter A, Wachtler M, Friebe C, Dietzek
B, Schubert US (2015) New ruthenium bis(terpyridine) metha-
nofullerene and pyrrolidinofullerene complexes: synthesis and
electrochemical. Photophysical Properties Inorg Chem 54:3159
– 3171
29. Motokawa N, Matsunaga S, Takaishi S, Miyasaka H, Yamashita
M, Dunbar KR (2010) Reversible magnetism between an antifer-
romagnet and a ferromagnet related to solvation/desolvation in a
robust layered [Ru2]2TCNQ charge-transfer system. J Am Chem
Soc 132:11943–11951
12. Medlycott EA, Hanan GS (2005) Designing tridentate ligands
for ruthenium(II) complexes with prolonged room temperature
luminescence lifetimes. Chem Soc Rev 34:133–142
13. Medlycott EA, Hanan GS (2006) Synthesis and properties of
mono- and oligo-nuclear Ru (II) complexes of tridentate ligands:
the quest for long-lived room temperature excited states. Coord
Chem Rev 250:1763–1782
30. Vögtle F, Plevoets M, Nieger M, Azzellini GA, Credi A, Cola LD,
Marchis VD, Venturi M, BalzaniV (1999) Dendrimers with a pho-
toactive and redox-active [Ru(bpy)3]2+-type core: photophysical
properties, electrochemical behavior, and excited-state electron-
transfer reactions. J Am Chem Soc 121:6290–6298
31. Jablonska-Wawrzycka A, Rogala P, Michałkiewicz S, Hodoro-
wiczb M, Barszcza B (2013) Ruthenium complexes in different
oxidation states: synthesis, crystal structure, spectra and redox
properties. Dalton Trans 42:6092–6101
14. Jiang H, Lee SJ, Lin W (2002) Chiral hybrid metal – organic
dendrimers. Org Lett 4:2149–2152
15. Chaignon F, Torroba J, Blart E, Borgstrom M, Hammarstrom
L, Odobel F (2005) Distance-independent photoinduced energy
transfer over 1.1 to 2.3 nm in ruthenium trisbipyridine–fullerene
assemblies. New J Chem 29:1272–1284
32. Clarke MJ (2003) Ruthenium metallopharmaceuticals. Coord
Chem Rev 236:209–233
33. Van der Drift RC, Bouwman E, Drent E (2002) Homogeneously
catalysed isomerisation of allylic alcohols to carbonyl compounds.
J Organomet Chem 650:1–24
16. Allen BD, Benniston AC, Harriman A, Mallon LJ, Pariani C
(2006) Competing through-space and through-bond, intramo-
lecular triplet-energy transfer in a supposedly rigid ruthenium(II)
tris(2,2′-bipyridine)–fullerene molecular dyad. Phys Chem Chem
Phys 8:4112–4118
34. Tianzhi Yu Chengcheng, Zhang Yuling, Zhao ShaoQiang, Guo
Peng, Liu Wentao, Li, Duowang Fan (2013) Synthesis, crystal
structure and photoluminescence of a cyclometalated Iridium(III)
coumarin complex. J Fluoresc 23:777–783
1 3

J Fluoresc
35. Lakshmanan R, Shivaprakash NC, Sindhu S (2015) Spectral char-
acterizations and photophysical properties of one-step synthesized
blue fluorescent 4′-aryl substituted 2, 2′: 6′, 2′′-terpyridine for
OLEDs application. J Lumin 168:145–150
45. Sinkeldam RW, Greco NJ, Tor Y (2010) Fluorescent analogs of
biomolecular building blocks: design, properties, and applica-
tions. Chem Rev 110:2579–2619
46. Santoni MP, Medlycott EA, Hanan GS, Hasenknopf B, Proust
A, Nastasi F, Campagna S, Chiorboli C, Argazzid R, Scandola F
(2009) Photoinduced energy transfer in a rod-like dinuclear Ru(II)
complex containing bis-pyridyl-1,3,5-triazine ligands.. Dalton
Trans 3964–3970
36. Frisch MJ et al (2009) Gaussian 09, revision A.02. Gaussian, Inc.,
Wallingford, CT
37. Miyasaka H, Campos-Fernández CS, Clérac R, Dunbar KR (2000)
Hexagonal layered materials composed of [M2(O2CCF3)4] (M =
Ru and Rh) donors and TCNQ acceptors. Angew Chem Int Ed
39:3831–3835
47. Breivogel A, Hempel K, Heinze K (2011) Inorg. Dinuclear bis
(terpyridine) ruthenium (II) complexes by amide coupling of
ruthenium amino acids: synthesis and properties. Chim Acta
374:152–162
38. Motokawa N, Oyama T, Matsunaga S, Miyasaka H, Sugimoto K,
Yamashita M, Lopez N, Dunbar KR (2008) A ladder based on
paddlewheel diruthenium(II, II) rails connected by TCNQ rungs:
a polymorph of the hexagonal 2-D network phase. Dalton Trans
4099–4102
48. Brown DG, Sanguantrakun N, Schulze B, Schubert US, Ber-
linguette CP (2012) Bis(tridentate) ruthenium–terpyridine com-
plexes featuring microsecond excited-state. Lifetimes J Am Chem
Soc 134:12354 – 12357
39. Stone ML, Crosby GA (1981) Charge-transfer luminescence from
ruthenium(II) complexes containing tridentate ligands. Chem
Phys Lett 79:169–173
49. Amirnasr M, Nazeeruddin MK, Gratzel M (2000) Thermal
stability of cis-dithiocyanato(2,2′-bipyridyl4,4′dicarboxylate)
ruthenium(II) photosensitizer in the free form and on nanocrys-
talline TiO 2 films. Thermochim Acta 348:105–114
50. Gherab KN, Gatri R, Hank Z, Dick B, Kutta RJ, Winter R, Luc J,
Sahraoui B, Fillaut JL (2010) Design and photoinduced surface
relief grating formation of photoresponsive azobenzene based
molecular materials with ruthenium acetylides. J Mater Chem
20:2858–2864
40. Coe BJ, Thompson DW, Culbertson CT, Schoonover JR,
Meyer TJ (1995) Synthesis and photophysical properties of
mono(2,2′,2′’-terpyridine) complexes of ruthenium(II). Inorg
Chem 34:3385–3395
41. Constable EC, Housecroft CE, Schofield ER, Encinas S, Armaroli
N, Barigelletti F, Flamigni L, Figgemeierc L, Vos JG (1999)
Luminescent molecular wires with 2,5-thiophenediyl spacers
linking {Ru(terpy)2} units. Chem Commun 869–870
42. Priyarega S, Muthu tamizh M, Karvembu R, Prabhakaran R,
Natarajan K, (2011) Synthesis, spectroscopic characterization
and catalytic oxidation properties of ONO/ONS donor schiff base
ruthenium(III) complexes containing PPh3/AsPh3. 123:313–325
43. Winkler JR, Netzel TL, Creutz C, Sutin N (1987) Direct obser-
vation of metal-to-ligand charge-transfer (MLCT) excited states
of pentaammineruthenium(II) complexes. J Am Chem Soc
109:2381–2392
51. Nazeeruddin MK, Amirnasr M, Comte P, Mackay JR, McQuillan
AJ, Houriet R, Gratzel M (2000) Adsorption studies of counte-
rions carried by the sensitizer cis-dithiocyanato(2,2′-bipyridyl-
4,4′-dicarboxylate) ruthenium(II) on nanocrystalline TiO2 Films.
Langmuir 16:8525–8528
52. McCusker CE, Chakraborty A, Castellano FN (2014) Excited state
equilibrium induced lifetime extension in a dinuclear platinum(II)
complex. J Phys Chem A 118:10391 – 10399
53. Hu JS, Ji HX, Cao AM, Huang ZX, Zhang Y, Wan LJ, Xia AD, Yu
DP, Meng XM, Lee ST (2007) Facile solution synthesis of hex-
agonal Alq3 nanorods and their field emission properties. Chem
Commun 3083–3085
44. Hutchison K, Morris JC, Nile TA, Walsh JL (1999) Spectro-
scopic and photophysical properties of complexes of 4′-ferro-
cenyl-2,2′:6′,2’ ‘-terpyridine and related ligands. Inorg Chem
38:2516–2523
1 3