New iridium complexes(III) bearing 2-phenylimidazo[4,5-f][1,10]-phenanthroline ligand: Synthesis, characterization, electrochemical and photoluminescence studies

Article abstract of DOI:10.1016/j.molstruc.2020.129415

Iridium complexes bearing 2-phenylimidazo[4,5-f]-[1,10]-phenanthroline with different substituents (-CH₃, -CH(CH₃)₂, -OCH₃, -C₆H₅) were synthesized and characterized. The effects of differe

Full text of DOI:10.1016/j.molstruc.2020.129415

Journal of Molecular Structure 1226 (2021) 129415
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
New iridium complexes(III) bearing
2-phenylimidazo[4,5-f][1,10]-phenanthroline ligand: Synthesis,
characterization, electrochemical and photoluminescence studies
Cigdem Sahin∗, Murat Sahin
Department of Chemistry, Art&Science Faculty, Pamukkale University, Denizli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Iridium complexes bearing 2-phenylimidazo[4,5-f]-[1,10]-phenanthroline with different substituents (-
CH3, -CH(CH3)2, -OCH3, -C6H5) were synthesized and characterized. The effects of different substituents
and solvents on the photoluminescence properties of the complexes with [Cl] and [PF6] counter anions
have been investigated. The synthesized complexes show high photoluminescence quantum yield due to
the extension of the π-electron conjugation of 2-phenylimidazo[4,5-f][1,10]-phenanthroline ligands. The
results indicate that the choice of counter anions ([Cl] and [PF6]) has an important influence on the
quantum yield of the complexes. In toluene, the compound 4 with phenyl substituent exhibits excimer
emission with increasing solution concentrations in the presence of [Cl] counter anion. The linear corre-
lation was observed between the redox potentials of the complexes and Hammett Substituent Constants.
The linear correlation can allow the prediction of the effects of substituents on electrochemical studies.
Received 8 June 2020
Revised 5 October 2020
Accepted 6 October 2020
Available online 7 October 2020
Keywords:
Iridium complex
Counterion
Photoluminescence
Phenanthroline
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
of counter anions can influence intermolecular interaction, molec-
ular aggregation and concentration quenching process for the com-
In recent years, phosphorescent metal complexes such as ruthe-
nium, iridium or platinum have attracted interest due to their po-
tential applications in optoelectronic devices [1], chemoreceptors
[2], biosensors [3]. Among these complexes, iridium complexes are
the most popular in organic light emitting diodes (OLEDs) due to
color tunability, shorter radiative lifetime and high quantum yields
[4,5]. The high quantum yields of iridium complexes are related
to mixing the singlet and the triplet excited states by strong spin-
orbit coupling [6,7]. The photochemical, photophysical and electro-
chemical properties of iridium complexes can be tuned by vary-
ing the ligands [6]. The design of ancillary ligands can affect the
quantum yield, excited state dynamics, HOMO and LUMO energy
levels which are important to improve the efficiency of OLED de-
vices [8,9]. 2-phenylimidazo[4,5-f][1,10]-phenanthroline derivatives
as ancillary ligands can be good candidates for the iridium com-
plexes due to rigid structure and their extended conjugation [10].
The rigid conjugated ligands in iridium complexes can lead to ef-
ficient spin-orbit coupling which can decrease nonradiative transi-
tions. This may result an increase in the quantum yields of irid-
ium complexes [11,12]. The counterions of the complexes can also
have an important effect on photophysical properties. The choice
plexes [13,14].
In this work, iridium complexes bearing 2-phenylimidazo[4,5-
f]-[1,10]-phenanthroline with different substituents (-CH3,
-
CH(CH3)2, -OCH3, -C6H5) and 2-(3-fluorophenyl)-4-methylpyridine
were synthesized. Our aim in synthesis of the complexes is to
increase the quantum yield of the molecules by using conjugated
ligands. The complexes exhibit high quantum yield in the pres-
ence of 2-phenylimidazo[4,5-f][1,10]-phenanthroline derivatives
as ancillary ligands. The effect of [Cl] and [PF6] counter anions
on electrochemical and photophysical properties of the com-
plexes have been investigated. The thermal, electrochemical and
photophysical properties of the synthesized complexes can be
appropriate for OLED applications.
2. Experimental section
2.1. Materials
Iridium(III) trichloride hydrate, 3-fluoro phenylboronic acid,
2-bromo-4-methylpyridine, 1,10-phenanthroline, tetrabutylammo-
nium hexafluorophosphate (TBAPF6), tetrakis(triphenylphosphine)
palladium(0) were provided from Aldrich. 4-methoxybenzaldehyde
and potassium hexafluorophosphate was obtained from Alfa
Aesar. 4-isopropylbenzaldehyde, 4-biphenylcarboxaldehyde, p-
∗
Corresponding author.
E-mail address: cigdemsahin82@gmail.com (C. Sahin).
https://doi.org/10.1016/j.molstruc.2020.129415
0022-2860/© 2020 Elsevier B.V. All rights reserved.

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
Scheme 1. Synthetic route of the compounds (1–8).
tolualdehyde were obtained from Acros. 1,10-phenanthroline-
5,6-dione [15], 2-(3-fluorophenyl)-4-methylpyridine (FMeppy)
[16] and [(FMeppy)2Ir(μ-Cl)]2 [17] were prepared according to the
literature. All reactions were performed using standard Schlenk
techniques under argon atmosphere.
2.2. Measurements
The absorption and photoluminescence (PL) measurements
were performed using Shimadzu UV-1601 UV-Vis spectrophotome-
ter and Perkin Elmer LS55 fluorescence spectrometer, respectively.
Mass spectra were obtained using Bruker Microflex LT MALDI-TOF
MS. ATR-FTIR spectra were performed using Perkin Elmer Spec-
trum Two FT-IR Spectrometer with a diamond ATR. NMR spectra
were obtained using Varian VNMRJ 400 NMR instrument. Tetram-
ethylsilane (TMS) was used as reference material for the reported
chemical shifts. The thermal data of the complexes were ob-
tained by Netzsch STA 449F5 instrument. Electrochemical data
were recorded on CH Instrument 660 B Model Electrochemical
Workstation.
Fig. 1. TGA curves of the compounds (1–4).
2.3. Synthesis and characterization
mmol), 1,10-phenanthroline-5,6-dione (0.12 mmol), ammonium
acetate (2.38 mmol) and glacial acetic acid (4.5 mL) was refluxed
for 5 h under argon atmosphere. After the mixture was cooled
to room temperature, the solution was neutralized with aqueous
ammonia solution. The resulting solid was filtered and washed
with ethanol. The dried product was obtained as a yellow powder.
2-(4-methylphenyl)-1H-imidazo-[4,5-f]-[1,10]-phenanthroline
(L1): 57% yield. FTIR (ATR, cm−1): 3346, 3021-3041, 2881-2921,
1606, 1551. 1H NMR (CDCl3, 400 MHz) δ ppm: 8.82 (s, 4H), 8.14
(d, 2H), 7.42 (s, 2H), 7.20 (d, 2H), 2.30 (s, 3H). 13C NMR (DMSO-d6,
2.3.1. Synthesis of ligands
2-(4-methylphenyl)-1H-imidazo-[4,5-f]-[1,10]-phenanthroline
(L1)
[18],
2-(4-isopropyl
(L2),
phenyl)-1H-imidazo-[4,5-f]-[1,10]-
phenanthroline
2-(4-methoxyphenyl)-1H-imidazo-[4,5-
ꢀ
f]-[1,10]-phenanthroline (L3) [19,20], 2-([1,1 -biphenyl]-4-yl)-
1H-imidazo-[4,5-f]-[1,10]-phenanthroline (L4) [21] were pre-
pared according to the literature procedures starting from p-
tolualdehyde, isopropylbenzaldehyde, 4-methoxybenzaldehyde, 4-
biphenylcarboxaldehyde, respectively. A mixture of aldehyde (0.12
2

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
Fig. 2. UV-Vis absorption spectra of 3 × 10−6 M solution of the compounds (1–8) in chlorobenzene.
Fig. 3. PL spectra of 3 × 10−6 M solution of the compounds (1-8) in different solvents (CH2Cl2, chlorobenzene, toluene).
3

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
Fig. 4. PL spectra of 3 × 10−7 M, 5 × 10−7 M, 8 × 10−7 M, 1 × 10−6 M, 3 × 10−6 M solutions of the compounds (1 and 4) in different solvents (dichloromethane,
chlorobenzene, toluene).
Fig. 5. The excitation spectra of of 3 × 10−7 M, 5 × 10−7 M, 8 × 10−7 M, 1 × 10−6 M, 3 × 10−6 M solutions of the compounds (1 and 4) in toluene.
4

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
Fig. 6. Cyclic voltammograms of the compounds (1–8) measured with scan rate is 100 mV s−1 in acetonitrile solution.
100.57 MHz) δ ppm: 151.3, 148.2, 143.8, 139.9, 130.0, 127.6, 126.7,
123.8, 21.4. MALDI-TOF MS (m/z): 311.430 [M+H]+.
1H), 8.63 (d, 2H) 8.21 (d, 1H), 8.10 (d, 1H), 7.76 (d, 2H), 7.67
(d, 1H), 7.61 (d, 1H), 7.43 (dt, 1H) 7.35 (d, 2H), 7.15 (d, 1H), 7.11
(d, 1H), 7.07 (d, 1H), 6.77 (td, 2H), 6.67 (dd, 2H), 6.56 (d, 1H),
6.28 (dt, 2H), 2.48 (d, 3H), 2.42 (d, 6H). 13C NMR (DMSO-d6,
100.57 MHz) δ ppm: 167.47, 165.62, 158.92, 151.09, 148.86, 146.01,
144.50, 140.85, 132.42, 132.09, 132.05, 130.24, 129.06, 127.65,
127.04, 125.70, 124.65, 121.66, 117.56, 117.37, 111.88, 101.67, 21.46,
21.01. MALDI-TOF MS (m/z): 874.872 [M-Cl]+.
2-(4-isopropylphenyl)-1H-imidazo-[4,5-f]-[1,10]-phenanthroline
(L2): 64% yield. FTIR (ATR, cm−1): 3380, 3030-3060, 2930-2965,
1605, 1543. 1H NMR (CDCl3, 400 MHz) δ ppm: 9.03 (d, 2H), 8.95
(d, 2H), 8.24 (d, 2H), 7.21 (d, 2H), 7.03 (d, 1H), 6.95 (d, 1H), 2.51 (d,
1H), 1.65 (d, 6H). 13C NMR (DMSO-d6, 100.57 MHz) δ ppm: 152.1,
148.3, 142.9, 139.5, 131.1, 127.3, 126.4, 123.5, 30.2, 22.8. MALDI-TOF
MS (m/z): 339.372 [M+H]+.
[Ir(FMeppy)2L2][Cl] (2): 56% yield. FTIR (ATR, cm−1): 3375,
3046, 2960, 2923, 1621, 1548, 1479, 1442, 1362, 1263, 1176, 811,
748. 1H NMR (CDCl3, 400 MHz) δ ppm: 10.56 (s, 1H), 9.28 (s, 1H),
8.64 (d, 2H), 8.23 (d, 1H), 8.13 (m, 1H), 7.76 (m, 2H), 7.67 (d, 1H),
7.61 (d, 1H), 7.43 (dd, 3H), 7.16 (d, 1H), 7.11 (d, 1H), 7.07 (d, 1H),
6.77 (td, 2H), 6.66 (m, 2H), 6.55 (s, 1H), 6.29 (d, 2H), 2.97 (m, 1H),
2.48 (d, 3H), 2.42 (d, 3H), 1.29 (d, 6H). 13C NMR (DMSO-d6, 100.57
MHz) δ ppm: 167.23, 166.23, 165.62, 158.96, 153.48, 151.07, 148.67,
145.54, 144.50, 144.24, 142.36, 140.88, 132.00, 130.22, 129.00,
127.02, 125.69, 124.64, 121.64, 117.56, 112.00, 103.07, 33.2, 22.10.
MALDI-TOF MS (m/z): 904.838 [M+1-Cl]+.
2-(4-methoxyphenyl)-1H-imidazo-[4,5-f]-[1,10]-phenanthroline
(L3): 52% yield. FTIR (ATR, cm−1): 3375, 3040-3065, 2890-2910,
1603, 1576. 1H NMR (CDCl3, 400 MHz) δppm: 9.9 (d 1H), 9.01 (d,
1H), 8.17 (s, 1H), 8.04 (s, 1H), 7.85 (d, 2H), 7,52 (d, 1H), 7.02 (d,
3H), 6.95 (s, 1H), 3.90 (t, 3H). 13C NMR (DMSO-d6, 100.57 MHz)
δ ppm: 160.9, 151.3, 148.2, 143.7, 131.7, 130.1, 128.9, 123.9, 114.9,
55.8. MALDI-TOF MS (m/z): 327.189 [M+H]+.
ꢀ
2-([1,1 -biphenyl]-4-yl)-1H-imidazo-[4,5-f]-[1,10]-
phenanthroline (L4): 60% yield. FTIR (ATR, cm−1): 3372, 3050-3080,
1605, 1548. 1H NMR (CDCl3, 400 MHz) δ ppm: 8.82 (s, 2H), 8.76
(d, 2H) 8.26 (d,2H) 7.55 (t, 3H), 7.35 (m, 6H). 13C NMR (DMSO-d6,
100.57 MHz) δ ppm: 150.9, 148.3, 146.3, 143.87, 139.63, 130.6,
130.2, 129.6, 129.5, 129.4, 127.3, 127.1, 123.8. MALDI-TOF MS (m/z):
373.504 [M+H]+.
[Ir(FMeppy)2L3][Cl] (3): 69% yield. FTIR (ATR, cm−1): 3389,
3045, 2948, 2910, 1615, 1547, 1479, 1440, 1362, 1249, 1177, 819,
743. 1H NMR (CDCl3, 400 MHz) δ ppm: 10.52 (s, 1H), 9.30 (d, 2H),
8.69 (m, 2H), 8.09 (m, 2H), 7.77 (d, 2H), 7.68 (d, 1H), 7.61 (d, 1H),
7.44 (m, 2H), 7.16 (d, 1H), 7.07 (m, 2H), 6.77 (m, 2H), 6.69 (d, 1H),
6.65 (d, 1H), 6.59 (m, 1H), 6.31 (t, 1H), 6.25 (m, 1H), 3.87 (dd, 3H),
2.50 (dd, 3H), 2.43 (dd, 3H). 13C NMR (DMSO-d6, 100.57 MHz) δ
ppm: 167.67, 166.25, 165.63, 161.56, 161.47, 161.28, 158.91, 151.31,
151.09, 148.86, 145.56, 144.25, 139.52, 132.69, 132.43, 129.70,
128.75, 127.49, 127.31, 125.70, 125.24, 124.64, 123.91, 121.67, 117.37,
115.07, 110.00, 104.83, 55.89, 21.02. MALDI-TOF MS (m/z): 890.958
[M-Cl]+.
2.3.2. Synthesis of iridium complexes (1-4)
The corresponding compounds (1-4) were prepared using a
modified literature procedure [22]. [(FMeppy)2Ir(μ-Cl)]2 (0.022
mmol) and phenanthroline ligand (0.047 mmol) were refluxed in
ethanol (7 mL) for 24 h under argon atmosphere. After the mix-
ture was cooled to room temperature, the product precipitated
with diethyl ether. The solid was collected by filtration and pre-
cipitated again from dichloromethane/diethyl ether for purification.
The product was obtained as yellow solid.
[Ir(FMeppy)2L4][Cl] (4): 69% yield. FTIR (ATR, cm−1): 3368,
3034, 2963, 2908, 1619, 1546, 1476, 1441, 1362, 1260, 1176, 806,
794. 1H NMR (CDCl3, 400 MHz) δ ppm: 10.58 (s, 1H), 9.25 (s, 1H),
8.79 (d, 2H), 8.22 (d, 1H), 8.11 (d, 1H), 7.73 (dd, 4H), 7.65 (m, 4H),
7.46 (t, 3H), 7.38(d, 1H), 7.21 (s, 1H), 7.11 (d, 2H), 6.78 (td, 2H),
6.72 (m, 1H), 6.66 (t, 1H), 6.58 (m, 1H), 6.32 (t, 1H), 6.25 (m,
1H), 2.48 (s, 3H), 2.43 (s, 3H). 13C NMR (DMSO-d6, 100.57 MHz) δ
ppm: 165.63, 162.57, 161.27, 158.96, 152.39, 151.09, 148.89, 145.63,
Starting from L1, L2, L3, L4 ligands, [Ir(FMeppy)2L1][Cl],
[Ir(FMeppy)2L2][Cl], [Ir(FMeppy)2L3][Cl], [Ir(FMeppy)2L4][Cl] were
prepared, respectively (Scheme 1).
[Ir(FMeppy)2L1][Cl] (1): 58% yield. FTIR (ATR, cm−1): 3403,
3037, 2958, 2921, 1621, 1548, 1480, 1456, 1380, 1267, 1121, 820,
739. 1H NMR (CDCl3, 400 MHz) δ ppm: 10.56 (s, 1H), 9.32 (d,
5

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
Fig. 7. The correlation between σp and emission maxima of the compounds (1–4).
[Ir(FMeppy)2L1][PF6] (5): 61% yield. FTIR (ATR, cm−1): 3368,
3050, 2948, 2888, 1621, 1550, 1483, 1438, 1360, 1276, 1176, 812,
553. 1H NMR (CDCl3, 400 MHz) δ ppm: 9.93 (s, 1H), 9.23 (d, 1H),
8.42 (d, 2H) 8.17 (dd, 1H), 8.10 (dd, 1H), 7.77 (d, 2H), 7.67 (d,
1H), 7.61 (d, 1H), 7.44 (dd, 1H) 7.34 (d, 2H), 7.18 (d, 1H), 7.13 (d,
1H), 7.09 (d, 1H), 6.77 (td, 2H), 6.67 (dd, 2H), 6.62 (d, 1H), 6.30
(m, 2H), 2.48 (d, 3H), 2.41 (d, 6H). 13C NMR (DMSO-d6, 100.57
MHz) δ ppm: 175.62, 167.45, 166.21, 165.64, 158.91, 153.47, 151.07,
148.85, 145.54, 144.22, 140.86, 132.72, 132.04, 130.22, 129.05,
127.03, 125.67, 124.63, 121.64, 120.92 117.20, 111.84, 105.06, 102.83,
21.44, 20.87. 19 F NMR (CDCl3) δ ppm: -71.84 (d, 6F, PF6), -121.15
(dq, 2F). MALDI-TOF MS (m/z): 874.947 [M-PF6]+.
[Ir(FMeppy)2L2][PF6] (6): 59% yield. FTIR (ATR, cm−1): 3358,
3063, 2977, 2951, 1624, 1548, 1478, 1439, 1362, 1275, 1179, 817,
554. 1H NMR (CDCl3, 400 MHz) δ ppm: 9.90 (s, 1H), 9.26 (s,
1H), 8.43 (d, 2H), 8.17 (d, 1H), 8.10 (d, 1H), 7.77 (m, 2H), 7.67
(d, 1H), 7.61 (d, 1H), 7.43 (td, 3H), 7.17 (d, 1H), 7.10 (d, 1H),
7.06 (d, 1H), 6.78 (td, 2H), 6.68 (m, 3H), 6.29 (m, 2H), 2.99 (m,
1H), 2.49 (d, 3H), 2.43 (d, 3H), 1.30 (d, 6H). 13C NMR (DMSO-d6,
100.57 MHz) δ ppm: 175.64, 167.47, 166.23, 165.62, 155.27, 151.07,
144.61, 144.46, 144.22, 142.33, 141.15, 139.49, 132.49, 129.56,
129.12, 128.70, 128.56, 128.26, 127.84, 127.65, 127.47, 127.17, 125.66,
124.65, 123.82, 119.00, 105.23, 103.03, 21.02. MALDI-TOF MS (m/z):
937.863 [M-Cl]+.
2.3.3. Synthesis of iridium complexes (5-8)
The corresponding compounds (5-8) were prepared us-
ing procedure described in the literature with slight mod-
ifications [23]. [(FMeppy)2Ir(μ-Cl)]2 (0.022 mmol) and corre-
sponding phenanthroline ligand (0.047 mmol) were refluxed in
dichloromethane/methanol (6 mL, 2:1, v/v) for 12 h under ar-
gon atmosphere. After the mixture was cooled to room temper-
ature, KPF6 (12 mmol) was added and stirred for 3 hours. The
obtained solid was collected by filtration and precipitated again
from dichloromethane/diethyl ether for purification. The product
was obtained as yellow solid.
Starting from L1, L2, L3, L4 ligands, [Ir(FMeppy)2L1][PF6],
[Ir(FMeppy)2L2][PF6], [Ir(FMeppy)2L3][PF6], [Ir(FMeppy)2L4][PF6]
were prepared, respectively (Scheme 1).
6

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
148.86, 146.22, 145.54, 144.50, 142.36, 140.88, 132.72, 132.00,
130.21, 129.01, 127.03, 125.67, 124.65, 121.85, 121.64, 117.56, 112.00,
109.35, 103.07, 33.6, 23.7. 19 F NMR (CDCl3) δ ppm: -71.83 (d, 6F,
PF6), -121.12 (dq, 2F). MALDI-TOF MS (m/z): 904.527 [M+1-PF6]+.
[Ir(FMeppy)2L3][PF6] (7): 63% yield. FTIR (ATR, cm−1): 3372,
3066, 2950, 2895, 1615, 1551, 1480, 1439, 1363, 1256, 1179, 812,
555. 1H NMR (CDCl3, 400 MHz) δ ppm: 9.77 (s, 1H), 9.27 (d, 1H),
8.44 (m, 2H), 8.14 (m, 2H), 7.76 (m, 2H), 7.67 (d, 1H), 7.61 (d,
1H), 7.44 (m, 3H), 7.11 (d, 1H), 7.06 (dd, 2H), 6.78 (td, 2H), 6.70
(m, 2H), 6.62 (d, 1H), 6.29 (m, 2H), 3.88 (d, 3H), 2.49 (d, 3H),
2.43 (d, 3H). 13C NMR (DMSO-d6, 100.57 MHz) δ ppm: 179.70,
168.49, 165.62, 163.40, 161.53, 161.11, 158.91, 151.08, 149.01, 148.74,
148.20, 145.56, 144.38, 142.99, 132.98, 132.48, 132.28, 128.75,
127.59, 127.31, 125.70, 124.63, 122.24, 121.86, 121.11, 117.56, 117.36,
115.07, 111.81, 109.90, 55.80, 20.90. 19 F NMR (CDCl3) δ ppm: -71.80
(d, 6F, PF6), -121.44 (dq, 2F). MALDI-TOF MS (m/z): 890.563 [M-
PF6]+.
[Ir(FMeppy)2L4][PF6] (8): 67% yield. FTIR (ATR, cm−1): 3363,
3058, 2965, 2907, 1622, 1548, 1477, 1443, 1361, 1265, 1176, 815,
554. 1H NMR (CDCl3, 400 MHz) δ ppm: 9.44 (s, 2H), 8.43 (m,
2H), 8.23 (dd, 1H), 8.13 (dd, 1H), 7.73 (m, 4H), 7.60 (dd, 4H),
7.45 (td, 3H), 7.39 (d, 1H), 7.21 (d, 1H), 7.12 (m, 2H), 6.79 (td,
2H), 6.73 (m, 1H), 6.66 (t, 1H), 6.59 (td, 1H), 6.32 (dd, 1H), 6.26
(dd, 1H), 2.49 (d, 3H), 2.43 (d, 3H). 13C NMR (DMSO-d6, 100.57
MHz) δ ppm: 179.30, 166.25, 165.63, 159.08, 151.09, 148.89, 145.63,
144.61, 144.45, 144.20, 142.31, 141.22, 139.49, 132.42, 129.56,
129.11, 128.69, 128.55, 127.83, 127.66, 127.45, 127.17, 125.68, 124.65,
121.67, 117.59, 105.19, 102.91, 20.90. 19 F NMR (CDCl3) δ ppm: -71.89
(d, 6F, PF6), -121.60 (dq, 2F). MALDI-TOF MS (m/z): 937.458 [M-
PF6]+.
bound to iridium atom [26] and the carbon atom adjacent to N
atom of 2-phenylpyridine [24], respectively. The carbon signal of
phenanthroline ligand at 151 ppm is shifted to 166 ppm with the
coordination of ligand to iridium (Figure S2). The 19 F NMR spectra
of the compounds (5-8) were obtained to confirm the presence of
[PF6] counterion. The doublet peaks at -71.83 ppm were observed
in the presence of [PF6] anion for compounds (5-8) [27]. The FTIR
spectra of molecules show the characteristic peaks for the imida-
zole N–H stretch around 3375 cm−1. The mass spectra of the com-
plexes show the parent molecular ion [M-Cl]+ for complexes 1-4
and [M-PF6]+ for complexes 5-8 (Figure S1).
Thermal behaviors of the compounds (1-4) were investigated
using thermal gravimetric analysis (TGA) at a heating rate of
10°C/min under nitrogen atmosphere. The mass loss of the iridium
compounds is given in Table S1. The synthesized complexes (1-3)
show high thermal stability. The decomposition temperatures are
318°C, 346°C and 312°C for complexes 1, 2 and 3, respectively. The
high thermal stability can be attributed to the 2-phenylpyridine
ligands containing polar F atoms which can induce intermolecular
interaction [28].
The TGA curve of compound 1 (Fig. 1) shows two decom-
position steps in the temperature range 30-900°C. The first de-
composition step of compound 1 occurs between 30°C and 507°C
with 31.49% mass loss which is attributed to the elimination of
4-methylphenyl group of L1 ligand and two pyridine rings with
methyl units. In the second step, the mass loss of 24.77% is
observed between 507°C and 900°C due to the removal of the
1H-imidazo-[4,5-f]-[1,10]-phenanthroline. After this decomposition
step, the residue with the mass 43.74% may be assigned to two
fluoro units, two phenyl groups of 2-phenylpyridine ligands and
iridium [1,29]. The thermal decompositions of compounds 2 and
3 occur at two steps. Firstly, the imidazole moiety and substituted
phenyl group of corresponding ligand and two methyl units of 2-
phenylpyridine ligands undergo decomposition in the temperature
range 30°C and 507°C. After this decomposition step, the mass loss
is around 24.00% corresponding to the elimination of the two flu-
oro units and phenanthroline part of corresponding ligand. The
residue with 55% may be associated with two 2-phenylpyridine lig-
ands and iridium. The thermal decomposition steps of compound
4 are shown in Table S1. Compound 4 shows lower decomposition
temperature (221°C) than other compounds (1-3) in the presence
of the phenyl group on L4 ligand [6]. The obtained results show
that the thermal decompositions of synthesized compounds are fa-
vorable for OLED applications [10].
3. Results and discussion
3.1. Structural characterization
The 1H NMR spectrum of L1 ligand shows proton signal as sin-
glets at 2.29 ppm which is attributed to the –CH3 substituent on
the phenyl ring. The signals at 2.51 ppm and 1.65 ppm are as-
signed to –CH and methyl groups in L2 ligand, respectively. Char-
acteristic proton signal of methoxy substituent of L3 is observed at
3.76 ppm. In addition, the NH proton of imidazole ring is not ob-
served in the 1H NMR spectra of phenanthroline ligands. It can be
attributed to fast exchange of a proton between the two N atoms
of the imidazole ring in solution [20]. The iridium complexes were
characterized by 1H NMR, 13C NMR and mass spectroscopies. In
the 1H NMR spectra of the compounds (1-3 and 5-7), the inte-
grated intensities of aromatic signals exhibit 22 protons (27 pro-
tons for compounds 4 and 8) in the range of 9.30-6.30 ppm which
can which can prove the presence of two 2-phenylpyridine and
one phenanthroline ligand (Figure S1). In the aliphatic region, the
two peaks at 2.48 and 2.42 ppm are associated with the –CH3 sub-
stituent of the 2-phenylpyridine of iridium compounds. The peaks
at 7.76 ppm and 6.30 ppm may be associated with the coordi-
nation of the NC-type of 2-phenylpyridine as bidentate [24]. The
peaks of proton adjacent to N atoms of phenanthroline ligand are
shifted from 8.82 ppm to 8.64 ppm upon coordination to iridium.
The peak at around 10.56 ppm was observed due to the NH pro-
ton of imidazole ring in complexes. It was reported that the NN-
type phenanthroline ligands as bidentate can coordinate to iridium
in [Ir(C^N)2(N^N)] type complex [11,25]. The proton signals of 1H-
imidazo-[4,5-f]-[1,10]-phenanthroline ligands of complexes at 7.61,
7.43, 7.11, 7.07 ppm are good agreement with the reported the re-
lated classes of iridium complexes containing 2-phenylpyridine and
phenanthroline ligands as bidentate [11,25]. In the 13C NMR spectra
of the compounds, the peaks at around 145.9 ppm and 150.9 ppm
are attributed to the cyclometalation carbon of 2-phenylpyridine
3.2. Absorption and photoluminescence studies
The absorption spectra of 3×10−6 M solution of the compounds
(1-8) in chlorobenzene are shown in Fig. 2 and corresponding data
are summarized in Table 1. The absorption bands of compounds
(1-8) around 312 nm are assigned to the spin-allowed 1π→π∗
transitions of both 2-phenylpyridine and phenanthroline ligands.
The lower energy absorption bands of the complexes at 426 nm
are associated with mixing singlet and triplet metal ligand charge
transfer (1MLCT and 3MLCT) transitions and 3π→π∗ transitions
which are caused by the spin-orbit coupling of iridium metal cen-
ter [10].
The photoluminescence properties of the compounds with [Cl]
counterion (1-4) were investigated in different solvents (toluene,
chlorobenzene, dichloromethane) at room temperature. The com-
pounds 1, 2 and 4 exhibit similar PL spectra which give green
emission bands around 545 nm in chlorobenzene and around 551
nm in dichloromethane (Fig. 3). However, the spectrum of com-
pound 3 exhibits red shift compared to other compounds (1, 2 and
4) due to the electron donor characteristic of the -OCH3 group [30].
7

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
Table 1
Absorption and emission data of the compounds (3 × 10−6 M) in different solvents (Toluene, chlorobenzene, CH2Cl2).
Complex
Toluene
abs
mx
Chlorobenzene
abs
mx
CH2Cl2
abs
mx
em
mx
abs
mx
abs
σp
λ
(nm)
λ
(nm)
λ
(nm)
λ
(nm)
λ
(nm)
λ (nm)
mx
ꢀPL
1
2
3
4
5
6
7
8
-0.17
-0.15
-0.27
-0.01
-0.17
-0.15
-0.27
-0.01
310, 356, 422
310, 362, 423
313, 366, 424
317, 367, 427
283, 343, 426
285, 342, 426
283, 341, 429
285, 343, 428
543
543
541
312, 360, 426
309, 361, 426
314, 364, 426
314, 362, 426
301, 362, 428
301, 362, 428
302, 367, 430
307, 354, 428
545
545
559
547
549
549
559
546
284, 332, 414
284, 334, 414
292, 339, 420
294, 342, 419
272, 331, 415
272, 331, 415
271, 333, 423
272, 332, 421
550
551
559
552
570
571
595
566
0.67
0.70
0.21
0.75
0.74
0.77
0.45
0.83
542, 600
545
545
546
543
σp values were obtained from [43].
In toluene, the compound 4 with phenyl substituent exhibits
interesting emission behavior which gives two emission bands at
542 nm and 600 nm, although it was expected that compound 4
may show broad single band like other compounds (1, 2, 3). It was
observed that the intensity ratio between the emission bands 542
nm and 600 nm increases from 0.80 to 1.11 (Fig. 4) and the exci-
tation bands are broadened with the increasing the concentrations
of solutions of compound 4 from 3×10−7 to 3×10−6 M (Fig. 5) [6].
This can be attributed to the excimer emission of the molecules
which can be caused by increasing intermolecular interactions in
toluene as nonpolar solvent [31,32]. In toluene, the compound 4
molecules can easily contact each other by the reduction of the
interactions between the complex and solvent molecules [32]. So,
the π-π interactions of phenyl group in compound 4 may increase
and result the formation of excimer. Among the compounds con-
taining phenyl substituents, the compound 8 with [PF6] counte-
rion exhibits broad single band and denotes no excimer formation
in contrast to the compound 4 with [Cl] counterion. It is known
oxidation peaks at around 1.22 V and 1.50 V can be associ-
ated with the metal-centered Ir(III)/Ir(IV) oxidation couple and the
phenyl fragment of 2-phenylpyridine, respectively [36,38]. The re-
duction peaks are observed at around -1.19 V and -1.47 V are
due to the pyridine fragment of 2-phenylpyridine and phenanthro-
line ligands, respectively. The oxidation potentials of compounds
4 and 8 containing phenyl group on 2-phenylimidazo[4,5-f]-[1,10]-
phenanthroline are slightly shifted to anodic area when compared
to the other compounds (1-3 and 5-7). It is attributed to the de-
localization of π electrons around the ring. When compare to the
electrochemical data of the compounds containing [Cl] counterion
(1-4), a similar trend was observed with the compounds containing
[PF6] counterion (5-8). This indicates that the counter anions (Cl−
and PF6−) do not have a significant effect on the electrochemical
properties of compounds.
The first oxidation and the first reduction potentials were used
for the determination the HOMO and LUMO energy levels of the
compounds using ferrocene as an internal standard (0.46 V vs.
Ag/Ag+) [39]. The energy levels of the compounds (1-8) are in
the range of 5.60 to 5.52 eV for HOMO levels and 3.16 to 3.13
eV for LUMO levels. The HOMO and LUMO energy levels of the
compounds suggest that these molecules can be used as dopant
in host materials, e.g. poly(N-vinyl carbazole) (PVK), 4,4’-bis(9-
carbazolyl)biphenyl (CBP), N,N’-Dicarbazolyl-3,5-benzene (mCP) for
OLED applications [40-42].
−
from literature [33] t−hat the anion size of PF6 is larger than Cl−.
The larger size of PF6 may decrease intermolecular interactions in
toluene which may prevent the formation of excimer. Furthermore,
it was observed that the emission maxima of the compounds are
slightly red-shifted with increasing polarity of solvents (toluene <
chlorobenzene < dichloromethane) (Table 1) [34].
The PL quantum yields of the compounds (1-8) were calcu-
lated according to the literature [34] and fac-Ir(bpy)3 was used as
the reference material (ꢀPL = 0.4 in toluene) [35]. The PL quan-
tum yields of the compounds with [Cl] counterion (1-4) were
found between 0.21 and 0.75 (Table 1). The PL quantum yields
of the synthesized compounds are slightly higher than the related
classes of iridium complexes containing mixtures of bipyridine and
phenanthroline ligands [30,36,37]. This can be related to the exten-
sion of the π-electron conjugation of 2-phenylimidazo[4,5-f][1,10]-
phenanthroline ligands which may result an increase in PL quan-
tum yields. The high quantum yields of the compounds are im-
portant to increase the performance OLED devices. With the aim
to obtain higher quantum yield in iridium complexes, the effect of
[Cl] and [PF6] counter anions on PL quantum yield have been in-
vestigated. Increased PL quantum yield was observed in the pres-
ence of [PF6] counter anion compared to the compounds with [Cl]
counterion (Table 1). The larger size of [PF6] counter anion may de-
crease intermolecular interactions and self-quenching which may
result an increase in quantum yield of compounds [13].
3.4. Correlation of the photophysical and electrochemical properties
with Hammett substituent constants
The photophysical and electrochemical properties of the iridium
complexes were correlated with the Hammett constants. The pho-
toluminescence maxima of the compounds with [Cl] counterion (1-
4) were plotted against the Hammett Substituent Constants (σp)
[43] in Fig. 7. The poor correlation was observed between pho-
toluminescence maxima and the Hammett constants of the sub-
stituents with a low regression coefficient (R2 =0.3721 in CH2Cl2,
R2 =0.4189 in chlorobenzene, R2 =0.1057 in toluene). However,
if the data point of compound 3 containing methoxy substituent
are not used for the account, the linear correlations can be ob-
served for photoluminescence maxima with regression coefficients
R2 =0.8421 in CH2Cl2, R2 =0.9868 in chlorobenzene, R2 =0.9868
in toluene (Fig. 7). This can be related to the strong interaction
methoxy substituent containing unshared electron pairs with ben-
zene ring by resonance effect. This interaction can result enhanced
the dipole moment of the complex which causes deviation from
the linear correlation [44]. Similar trends were observed in the cor-
relation of photophysical properties with the Hammett constants
for the compounds with [PF6] counterion (5-8) (Fig. S3).
3.3. Electrochemical data
The electrochemical measurements were performed using Ag
wire reference electrode, Pt wire counter electrode, glassy carbon
working electrode in acetonitrile with 0.1 M TBAPF6. The cyclic
voltammograms of the compounds (1-8) are shown in Fig. 6 and
the data are given in Table 2. The cyclic voltammograms of the
compounds exhibit two oxidation and two reduction peaks. The
The oxidation and reduction potentials of the compounds as a
function of Hammett Substituent Constants (σp) [43] were plotted
in Fig. 8. The good linear correlation between the oxidation and
reduction potentials of the compounds with [Cl] counterion (1-4)
8

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
Table 2
The electrochemical data of the compounds (1–8) in acetonitrile.
Complex
σp
Eox1 (V)
Eox2 (V)
Ered1 (V)
Ered2 (V)
HOMO (eV)
LUMO (eV)
Band gap (Eg) (eV)
1
2
3
4
5
6
7
8
-0.17
-0.15
-0.27
-0.01
-0.17
-0.15
-0.27
-0.01
1.22
1.22
1.20
1.26
1.20
1.20
1.18
1.23
1.50
1.51
1.50
1.53
1.54
1.53
1.54
1.54
-1.19
-1.19
-1.20
-1.18
-1.20
-1.20
-1.21
-1.19
-1.47
-1.47
-1.47
-1.48
-1.46
-1.46
-1.46
-1.45
-5.56
-5.56
-5.54
-5.60
-5.54
-5.54
-5.52
-5.57
-3.15
-3.15
-3.14
-3.16
-3.14
-3.14
-3.13
-3.15
2.41
2.41
2.40
2.44
2.40
2.40
2.39
2.42
σp values were obtained from [43].
Fig. 8. The correlation of σp with the Eox and Ered of the compounds (1–8).
and Hammett Substituent Constants (σp) was observed with re-
gression coefficients R² = 0,9792 and R² = 0,9826 (R² = 0,9932 and
R² = 0,9826 for the compounds with [PF6] counterion (5-8)), re-
spectively. Hammett correlations can be used to predict substituent
effect on electrochemical properties of compounds.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgement
4. Conclusion
We acknowledge the project support of Pamukkale University
(Project No: 2014FBE057).
In summary, we reported the synthesis of iridium complexes
containing 2-phenylimidazo[4,5-f]-[1,10]-phenanthroline with dif-
ferent substituents (-CH3, -CH(CH3)2, -OCH3, -C6H5) and the in-
vestigation of thermal, photophysical and electrochemical prop-
erties of the complexes. The synthesized complexes show ther-
mal stability and high quantum yield in the presence of 2-
phenylimidazo[4,5-f][1,10]-phenanthroline derivatives due to the
extension of the π-electron conjugation. The effects of [Cl] and
[PF6] counter anions on PL quantum yield have been investigated.
An increase in PL quantum yield of compounds was observed in
the presence of [PF6] counterion. The emission maxima of the
compounds are red-shifted with increasing polarity of solvents and
the formation of excimer is observed in the presence of phenyl
substituent for compound 4 with [Cl] counterion in toluene. HOMO
and LUMO energy levels of the compounds are calculated in the
range of 5.60 to 5.52 eV and 3.16 to 3.13 eV, respectively. These
results suggest that these molecules are promising candidates as
dopant in OLED applications.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2020.129415.
References
[1] A. Liang, J. Tang, P. Cai, X. Yang, W. Wu, L. Chen, Z. Wang, M. Cai,
F. Huang, Sky-blue phosphorescent organic light-emitting diodes with diben-
zo-24-crown-8 substituted iridium(III) complexes as the dopant, Dyes Pig-
ments 138 (2017) 77–82.
[2] H. Yang, Y. Zhu, L. Li, Z. Zhou, S. Yang, A phosphorescent chemosensor for
Cu2+ based on cationic iridium(III) complexes, Inorganic Chem. Commun. 16
(2012) 1–3.
[3] A.C. Carrasco, V. Rodríguez-Fanjul, A. Habtemariam, A.M. Pizarro, Structu-
ally strained half-sandwich iridium(III) complexes as highly potent anticancer
agents, J. Med. Chem. 63 (2020) 4005–4021.
[4] K.C. Pradhan, S. Barik, B.C. Singh, P. Mohapatra, H.K. Kisan, S. Pal, Synthesis,
characterisation and theoretical studies of a series of Iridium (III) heteroleptic
complexes with Schiff base ligands, J. Mol. Struct. 12115 (2020) 128058.
[5] Y. Zhou, W. Li, L. Yu, Y. Liu, X. Wang, M. Zhou, Highly efficient electrochemilu-
minescence from iridium(III) complexes with 2-phenylquinoline ligand, Dalton
Trans. 44 (2015) 1858–1865.
[6] C. Sahin, A. Goren, C. Varlikli, Synthesis, characterization and photophysi-
cal properties of iridium complexes with amidinate ligands, J. Organometallic
Chem. 772-773 (2014) 68–78.
Author Contributions Section
Cigdem Sahin: Synthesis and characterization of molecules,
Photoluminescence studies, Electrochemical and Thermogravi-
metric measurements, Hammett substituent constants studies,
Writing- Reviewing and Editing.
[7] S. Zhang, F. Wu, W. Yang, Y. Ding, Synthesis, characterization and photophysical
properties of two heteroleptic 2-(4,6-difluorophenyl)pyridyl iridium(III) com-
plexes with amidate ancillary ligands, Inorganic Chem. Commun. 14 (2011)
1414–1417.
Murat Sahin: Synthesis and characterization of molecules, Pho-
toluminescence studies.
9

C. Sahin and M. Sahin
Journal of Molecular Structure 1226 (2021) 129415
[8] E. Kabir, Y. Wu, S. Sittel, B.-L. Nguyen, T.S. Teets, Improved deep-red phospho-
rescence in cyclometalated iridium complexes via ancillary ligand modifica-
tion, Inorg. Chem. Front. 7 (2020) 1362–1373.
[9] A. Maity, K.K. Rajak, Photo induced trans→cis isomerism studies of heterolep-
tic iridium complex with 8-quinolinol-5-phenylazo ligand: Photophysical and
electrochemical studies and it’s theoretical investigations, J. Mol. Struct. 11815
(2019) 38–47.
[26] F.O. Garces, Richard J. Watts, ’H and 13C NMR assignments with coordi-
nation-induced shift calculations of carbon o-bonded ovtho-metalated rho-
clium(II1) and iridium(II1) complexes, Magnetic Reson. Chem. 31 (1993)
529–536.
[27] H. Na, A. Maity, T.S. Teets, Bis-cyclometalated iridium complexes with elec-
tronically modified aryl isocyanide ancillary ligands, Dalton Trans. 46 (2017)
5008–5016.
[10] H. Tang, Y. Li, Q. Chen, B. Chen, Q. Qiao, W. Yang, H. Wu, Y. Cao, Efficient yel-
low-green light-emitting cationic iridium complexes, based on 1,10-phenan-
throline derivatives containing oxadiazoletriphenylamine unit, Dyes Pigments
100 (2014) 79–86.
[28] B. Chen, Y. Li, W. Yang, W. Luo, H. Wu, Efficient sky-blue and blue-green
light-emitting electrochemical cells based on cationic iridium complexes us-
ing 1,2,4-triazole-pyridine as the ancillary ligand with cyanogen group in alkyl
chain, Organic Electron. 12 (2011) 766–773.
[11] X.-H. Yang, M. Li, H. Peng, Q. Zhang, S.-X. Wu, W.-Q. Xiao, X.-L. Chen, Z.-G. Niu,
G.-Y. Chen, G.-N. Li, Highly luminescent mono- and dinuclear cationic irid-
ium(III) complexes containing phenanthroline-based ancillary ligand, Eur. J. In-
org. Chem. (2019) 847–855.
[29] D. Chen, L. Han, D. Liu, K. Ye, Y. Liu, J. Zhang, Y. Wang, High performance
blue-green and green phosphorescent OLEDs based on iridium complexes with
N^C^N-coordinated terdentate ligands, RSC Adv. 5 (2015) 18328–18334.
[30] K. Hasan, A.K. Bansal, I.D.W. Samuel, C. Roldan-Carmona, H.J. Bolink,
E. Zysman-Colman, Tuning the emission of cationic iridium (iii) complexes to-
wards the red through methoxy substitution of the cyclometalating ligand, Sci-
entif. Rep. 5 (2015) 12325, doi:10.1038/srep12325.
[12] L. Wang, P. Cui, L. Lystrom, J. Lu, S. Kilina, W. Sun, Heteroleptic cationic
iridium(iii) complexes bearing phenanthroline derivatives with extended
π-conjugation as potential broadband reverse saturable absorbers, New J.
Chem. 44 (2020) 456–465.
[13] D. Ma, L. Duan, Y. Wei, L. He, L. Wang, Y. Qiu, Increased phosphorescent quan-
tum yields of cationic iridium(III) complexes by wisely controlling the counter
anions, Chem. Commun. 50 (2014) 530–532.
[31] J. Zhao, L. Liu, J. Wu, J. Yu, Spectral variation of solution-processed blue
bis[(4,6-difluorophenyl)-pyridinato-N,C2’] (picolinate) iridium(III) phosphor,
Dyes Pigments 102 (2014) 234–240.
[32] S. Takayasu, T. Suzuki, K. Shinozaki, Intermolecular interactions and aggre-
gation of fac-Tris(2-phenylpyridinato-C2’,N)iridium(III) in nonpolar solvents, J.
Phys. Chem. B 117 (2013) 9449–9456.
[33] J.N. Gayton, S. Autry, R.C. Fortenberry, N.I. Hammer, J.H. Delcamp, Counter
anion effect on the photophysical properties of emissive indolizine-cyanine
dyes in solution and solid state, Molecules 23 (2018) 3051, doi:10.3390/
molecules23123051.
[34] J. Xu, C. Yang, B. Tong, Y. Zhang, L. Liang, M. Lu, The effects of different sol-
vents and excitation wavelength on the photophysical properties of two novel
Ir(III) complexes based on phenylcinnoline ligand, J. Fluorescence 23 (2013)
865–875.
[14] G. Li, W. Guan, S. Du, D. Zhu, G. Shan, X. Zhu, L. Yan, Z. Su, M.R. Bryce,
A.P. Monkman, Anion-specific aggregation induced phosphorescence emission
(AIPE) in an ionic iridium complex in aqueous media, Chem. Commun. 51
(2015) 16924–16927.
[15] C. Zhong, H. Huang, A. He, H. Zhang, Synthesis and luminescent properties of
novel polymeric metal complexes with bis(1,10-phenanthroline) group, Dyes
Pigments 77 (2008) 578–583.
[16] H.S. Lee, Y. Ha, The new iridium(III) pyridyltetrazolate complexes for blue
phosphorescence, Mol. Crystals Liquid Crystals 504 (2009) 67–75.
[17] Y. Liu, K. Ye, Y. Fan, W. Song, Y. Wang, Z. Hou, Amidinate-ligated iridium(III)
bis(2-pyridyl)phenyl complex as an excellent phosphorescent material for elec-
troluminescence devices, Chem. Commun. 25 (2009) 3699–3701.
[18] Q.Y. Yu, J.F. Huang, Y. Shen, L.M. Xiao, J.M. Liu, D.B. Kuang, C.Y. Su, Novel
phenanthroline-based ruthenium complexes for dye-sensitized solar cells: en-
[35] L. Chen, Z. Ma, J. Ding, L. Wang, X. Jinga, F. Wang, Self-host heteroleptic green
iridium dendrimers: achieving efficient non-doped device performance based
on a simple molecular structure, Chem. Commun. 47 (2011) 9519–9521.
[36] S. Salinas, M.A. Soto-Arriaza, B. Loeb, New iridium cyclometallated complexes
with potential application in OLED, Polyhedron 30 (2011) 2863–2869.
[37] R. Cao, J. Jia, X. Ma, M. Zhou, H. Fei, Membrane localized iridium(III) complex
induces endoplasmic reticulum stress and mitochondria-mediated apoptosis in
human cancer cells, J. Med. Chem. 56 (2013) 3636–3644.
hancement in performance through fluoro-substitution, RSC Adv.
19311–19318.
3 (2013)
[19] X. Li, J. Gui, H. Yang, W. Wu, F. Li, H. Tian, C. Huang, A new carbazole-based
phenanthrenyl ruthenium complex as sensitizer for a dye-sensitized solar cell,
Inorganica Chimica Acta 361 (2008) 2835–2840.
[38] C. Sahin, A. Goren, S. Demir, M.S. Cavus, New amide based iridium(III) com-
plexes: synthesis, characterization, photoluminescence and DFT/TD-DFT stud-
ies, New J. Chem. 42 (2018) 2979–2988.
[20] L.F. Tan, F. Wang, H. Chao, Y.F. Zhou, C. Weng, Ruthenium(II)
mixed-ligand complex containing 2-(4’-benzyloxy-phenyl)imidazo[4,5-f][1,10]
phenanthroline: Synthesis, DNA-binding and photocleavage studies, Journal of
Inorganic Biochemistry 101 (2007) 700–708.
[39] B.S. Kim, S.H. Kim, Y.S. Kim, S.H. Kim, Y.A. Son, Synthesis and characteriza-
tion of quinoline-based dye sensor, Mol. Crystals Liquid Crystals 504 (2009)
173–180.
[21] L.F. Tan, H. Chao, Y.F. Zhou, L.N. Ji, Synthesis, characterization, DNA-binding and
DNA photocleavagestudies of [Ru(bpy)2(BPIP)]2+ and [Ru(phen)2(BPIP)]2+
[40] H. Tang, Z. Chen, L. Wei, J. Miao, G. Meng, Y. He, H. Wu, Three cationic
iridium(III) complexes with 1,10-phenanthroline or compounds containing
1,10-phenanthroline unit as auxiliary ligands: Synthesis and application in
polymer light-emitting diodes, Dyes Pigments 131 (2016) 340–348.
[41] H. Tang, L. Wei, G. Meng, Y. Li, G. Wang, F. Yang, H. Wu, W. Yang, Y. Cao,
Polymer light-emitting diodes based on cationic iridium(III) complexes with a
1,10-phenanthroline derivative containing a bipolar carbazole–oxadiazole unit
as the auxiliary ligand, Opt. Mater. 37 (2014) 679–687.
[42] K.S. Yook, S.O. Jeon, C.W. Joo, J.Y. Lee, High efficiency deep blue phosphorescent
organic light-emitting diodes, Organic Electron. 10 (2009) 170–173.
[43] C. Hansch, A. Leo, R.W. Taft, A survey of hammett substituent constants and
resonance and field parameters, Chem. Rev. 91 (1991) 165–195.
[44] F.H. Westheimer, The Electrostatic Effect of Substituents on the Dissociation
Constants of Organic Acids. IV. Aromatic Acids, J. Am. Chem. Soc. 61 (1939)
1977–1980.
(BPIP
=
2-(40-biphenyl)imidazo[4,5-f][1,10]phenanthroline), Polyhedron 26
(2007) 3029–3036.
[22] C. Dolan, R.D. Moriarty, E. Lestini, M. Devocelle, R.J. Forster, T.E. Keyes, Cell
uptake and cytotoxicity of a novel cyclometalated iridium(III) complex and its
octaarginine peptide conjugate, J. Inorganic Biochem. 119 (2013) 65–74.
[23] Q. Zhao, S. Liu, M. Shi, F. Li, H. Jing, T. Yi, C. Huang, Tuning photophysi-
cal and electrochemical properties of cationic iridium(III) complex salts with
imidazolyl substituents by proton and anions, Organometallics 26 (2007)
5922–5930.
[24] C. Liu, Linpo Yu, Y. Liu, F. Li, M. Zhou, NMR study on iridium(III) complexes for
identifying disulfonate substituted bathophenanthroline regio-isomers, Magn.
Reson. Chem. 49 (2011) 816–823.
[25] C. Jin, J. Liu, Y. Chen, G. Li, R. Guan, P. Zhang, L. Ji, H. Chao, Cyclometalated
iridium(III) complexes with imidazo[4,5-f][1,10]phenanthroline derivatives for
mitochondrial imaging in living cells, Dalton Trans. 44 (2015) 7538–7547.
10