New amide based iridium(III) complexes: Synthesis, characterization, photoluminescence and DFT/TD-DFT studies

Article abstract of DOI:10.1039/c7nj04671e

New iridium(iii) complexes with 2-(3-fluorophenyl)-4-methylpyridine as cyclometalated ligands and 2,2′-bipyridine-4,4′-dicarboxamide derivatives as ancillary ligands were synthesized and characterized by FTIR, NMR, MS, UV/Visible, and fluorescence spectroscopies and cyclic voltammetry. The effects of different solvents and substituents on the photophysical properties of the complexes have been investigated. The complexes show tunable photoluminescence wavelengths depending on solvent polarity in the 548 nm to 610 nm range where the emission colour can change from green to orange-red. The complexes exhibit high photoluminescence quantum yields between 0.41 and 0.75, which may be attributed to the change in the transition dipole moment originating from the amide group upon electronic excitation. The calculated HOMO and LUMO energy levels of complexes 1-7 are in the -5.51 to -5.60 eV and -3.37 to -3.40 eV ranges, respectively. The ground and excited state properties of 1 have been fully investigated by means DFT and TD-DFT methods respectively. The general trends of observed data have been successfully represented and quantified by computational data.

Full text of DOI:10.1039/c7nj04671e

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Pl Ne ae swe Jd oo u nr no at l ao dfj Cu sh te mm ai sr tgr iyn s
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DOI: 10.1039/C7NJ04671E
Journal Name
ARTICLE
New amide based iridium(III) complexes: Synthesis,
characterization, photoluminescence and DFT/TD-DFT studies
Received 00th January 20xx,
Accepted 00th January 20xx
a,*
a
b
c
Cigdem Sahin , Aysen Goren , Serkan Demir and Muhammet Serdar Cavus
DOI: 10.1039/x0xx00000x
New iridium(III) complexes with 2-(3-fluorophenyl)-4-methylpyridine as cyclometalated ligands and 2,2'-bipyridine-4,4'-
dicarboxamide derivatives as ancillary ligands were synthesized and characterized by FTIR, NMR, MS, UV/Visible,
fluorescence spectroscopies and cyclic voltammetry. The effects of different solvents and substituents on the
photophysical properties of the complexes has been investigated. The complexes show tunable photoluminescence
wavelengths depending on solvent polarity in the range of 548 nm to 610 nm where the emission colour can change from
green to orange-red. The complexes exhibit high photoluminescence quantum yields between 0.41 and 0.75 which may be
attributed to the change of transition dipole moment originating from amide group upon electronic excitation. The
calculated HOMO and LUMO energy levels of the complexes (1-7) are in the range of -5.51-(-5.60) eV and -3.37-(-3.40) eV,
respectively. Ground and excited state properties of 1 has been fully investigated by means DFT and TD-DFT methods
respectively. General trends of observed data have been successfully represented and quantified by computational data.
www.rsc.org/
9
-11
biimidazole, picolinate.
1
. Introduction
Based on the above requirements, our aim of strategy in
synthesis of new iridium complexes is to increase the quantum yield
and solubility of molecules by the use of amide substituted
bipyridine ligands. As an inherent feature of amide group, the lone
The
photophysical
and
photochemical
properties
of
photoluminescent second and third row transition metal complexes
such as Ru(II), Pt(II) and Ir(III) have great attention over the past few
decades owing to effective mixing of their singlet and triplet excited
pairs on nitrogen of amide can delocalize into the carbonyl group
12,13
which lead the change of the dipole moment of the group.
The
1
,2
states as a result of strong heavy metal spin-orbit coupling.
change of dipol moment can cause the increase of the number of
radiative transitions since the quantum yield depends on the ratio
Among them, cyclometalated Ir(III) complexes are of special
interest because of having high quantum yield, shorter lifetime,
14
between radiative and nonradiative transitions. Therefore we
3
,4,5
high thermal stability in organic light emitting diodes (OLEDs).
rationally estimated in this study that the addition of peripheral
amide groups in 2,2'-bipyridine-4,4'-dicarboxamide ligands changes
the dipole moment of the molecules upon electronic excitation and
Moreover, the emission colour of iridium complexes can be tuned
by the modification of cyclometalated and ancillary ligands which
6
cause destabilized d-d gap in iridium atom. Therefore, the design
hence results a reasonable increase in the quantum yield of the
of ligands and their iridium complexes have gained great interest
12,13
molecules.
Iridium complexes containing 2,2'-bipyridine-4,4'-
5
7
for their potential applications as OLED materials, chemosensors,
dicarboxamide derivatives as ancillary ligands are promising
candidates to achieve high quantum efficiency. Besides, the use of
alkyl chains and the benzyl groups may increase the solubility of
complexes and decrease intermolecular interactions which may
8
biosensors. Recently, solution-processed OLEDs gain great interest
due to the low fabrication cost and large area production. High
solubility, high quantum yield and thermal stability are desired for
9
,10
the use of iridium complexes in solution-processed devices.
15,16
reduce quenching process.
Many researchers have made efforts to improve the
photoluminescent efficiencies and solubility of iridium complexes
by the use of different ancillary ligands such as acetylacetonate,
In this work, iridium complexes containing 2,2'-bipyridine-4,4'-
dicarboxamide ligands with different substituents and 2-(3-
fluorophenyl)-4-methylpyridine were synthesized and characterized
1
by IR, H NMR and LC-MS/MS techniques. Experimentally studied
optical and electrochemical properties of the complexes have been
throughly investigated by DFT and TD-DFT methods. Based on the
results, the calculated data successfully correlated with the ones
obtained from experimental findings.
2
. Experimental
2
.1. Materials and measurements
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DOI: 10.1039/C7NJ04671E
ARTICLE
Journal Name
Propylamine, butylamine, pentylamine, hexylamine, octylamine, orbital (MO) compositions of the complexes were manipulated by
23
benzylamine, 2-phenylethylamine were obtained from Merck. 3- using Virtual Molecular Orbital designator, VMOdes program.
Fluorophenylboronic acid, 2-bromo-4-methylpyridine, 4,4’-
2
.5. TD-DFT calculations
dimethyl-2,2’-bipyridine, tetrakis (triphenylphosphine) palladium
0), sodium carbonate, iridium(III) trichloride hydrate were provided
from Aldrich. Tetrabutyl ammonium hexafluorophosphate (TBAPF
TD-DFT calculations in order to define vertical excitations involving
, S and T optimized geometries of the complexes were
(
S
0
1
1
6
)
1
7
performed. The same level of theory with that of SPE calculations
was used in order to obtain more correlated transition energies
with experimental optical data. First 15 singlet and triplet vertical
excitations were taken into account. MO contributions of the
was obtained from Fluka. 4,4’-dicarboxy-2,2’-bipyridine, 4,4’-
1
8
diethoxycarbonyl-2,2’-bipyridine,
2-(3-fluorophenyl)-4-
1
9
methylpyridine
(FMeppy),
N,N'-dioctyl-2,2'-bipyridine-4,4'-
2
0
21
dicarboxamide (L
5
)
and [(FMeppy)
2
Ir(ꢀ-Cl)]
2
were prepared
2
4,25
transitions were also computed by using SWizard software.
according to literature procedures. FTIR spectra were obtained
using Perkin Elmer Spectrum Two FT-IR Spectrometer with a
diamond ATR. NMR spectra were recorded on a Varian VNMRJ 400
Natural transition orbitals (NTOs) surfaces were generated from TD-
DFT data to qualify the nature of excitation and emission.
NMR instrument and tetramethylsilane (TMS) was used as internal 2.6. Synthesis and characterization
reference material for the reported chemical shifts. ESI-MS were
2
.6.1. N,N'-dipropyl-2,2'-bipyridine-4,4'-dicarboxamide (L
1
): N,
recorded in acetonitrile on an AB SCIEX QTRAP 5500 LC/MS/MS
System Mass Spectrometer. The absorption and photoluminescence
N'-dipropyl-2,2'-bipyridine-4,4'-dicarboxamide
was
prepared
according to the literature procedure described for 4,4’-
dioctylamido-2,2’-bipyridine except that propylamine was used
(PL) spectra were obtained using Shimadzu 1800 UV-Vis
spectrophotometer and Perkin Elmer LS55 fluorescence
spectrometer, respectively. Electrochemical studies were
performed in a three-electrode cell with using Drop Sens µStat 200
bipotentiostat. The three-electrode system was consisted of glassy
carbon working electrode, Ag wire reference electrode and Pt wire
20
instead of octylamine. A mixture of 4,4’-diethoxycarbonyl-2,2’-
bipyridine (55 mg, 0.167 mmol) and propylamine (2.5 mL) was
heated at 45 °C overnight under argon atmosphere. The resulting
white solid was filtered and washed with diethyl ether. The dried
-1
product was obtained with 87% yield. FT-ATR (cm ): 3283 (N-H);
counter electrode. The solution of 0.1 M TBAPF
used as supporting electrolyte.
6
in acetonitrile was
1
3
065 (Ar-H); 2951-2872 (aliph. C-H); 1635 (C=O); 1374 (C-N). H-
6
NMR (400 MHz, DMSO-d ) : δppm= 0,89 (t, 6H); 1,55 (m, 4H); 3,25
2.2. Computational protocol
(q, 4H); 7,83 (d, 2H); 8,76 (d, 2H); 8,84 (d, 2H); 8,91 (t, 2H).
N,N'-dibutyl-2,2'-bipyridine-4,4'-dicarboxamide, N,N'-dipentyl-2,
2'-bipyridine-4,4'-dicarboxamide, N,N'-dihexyl-2,2'-bipyridine-4,4'-
dicarboxamide, N,N'-dibenzyl-2,2'-bipyridine-4,4'-dicarboxamide, N,
N'-2-phenylethyl-2,2'-bipyridine-4,4'-dicarboxamide were prepared
All computations were performed by using Gaussian 09W program
2
2
suits running under Windows and Linux platform.
.3. Geometry optimizations
Ground state (S ), first singlet (S
geometries of the complexes were optimized in the gas phase at butylamine,
B3LYP/LANL2DZ level imposing C2 symmetry constrain. The initial phenylethylamine, respectively.
geometries of the complexes were constructed manually by GUI 2.6.2. N,N'-dibutyl-2,2'-bipyridine-4,4'-dicarboxamide (L
2
0
1
) and triplet (T
1
) excited state using the same procedure for L
1
starting from propylamine,
benzylamine, 2-
pentylamine, hexylamine,
2
):
-1
program considering the experimental data. All optimized White solid, yield 90%. FT-ATR (cm ): 3297 (N-H); 3047 (Ar-H);
1
structures were verified as local minima by subsequently performed 2958-2808 (aliph. C-H); 1632 (C=O); 1408 (C-N). H-NMR (400 MHz,
vibrational frequency calculations. For qualitative interpretation of DMSO-d
the observed redox behaviours of the complexes in solution, 4H); 7,82 (d, 2H); 8,76 (d, 2H); 8,84 (d, 2H); 8,90 (t, 2H).
polarizable continuum model (PCM) implemented geometry 2.6.3. N,N'-dipentyl-2,2'-bipyridine-4,4'-dicarboxamide (L
optimizations of N and N-1 electron states were performed in the White solid, yield 69%. FT-ATR (cm ): 3297 (N-H); 3048; 2951-2867
6
) : δppm= 0,89 (t, 6H); 1,33 (m, 4H); 1,58 (m, 4H); 3,28 (q,
3
):
-1
1
presence of acetonitrile medium.
(aliph. C-H); 1630 (C=O); 1357 (C-N). H-NMR (400 MHz, DMSO-d
6
) :
ppm= 0,86 (t, 6H); 1,30 (m, 8H); 1,54 (m, 4H); 3,27 (q, 4H); 7,82 (d,
H); 8,76 (d, 2H); 8,84 (d, 2H); 8,90 (t, 2H).
.6.4. N,N'-dihexyl-2,2'-bipyridine-4,4'-dicarboxamide (L
δ
2
2.4. SPE calculations at the optimized structures
Coulomb-attenuated method-B3LYP functional (CAM-B3LYP) was
applied for SPE calculations at the ground and excited state
geometries for more quantitative prediction of the energies of the
states as well as the vertical excitation energies corresponding to
absorptions and emissions. This functionals was proven to be
excellent complement to hybrid density functionals for more
accurate estimation of long range, charge transfer type and
2
4
):
-1
White solid, yield 80%. FT-ATR (cm ): 3302 (N-H); 3046 (Ar-H);
1
2
954-2937 (aliph. C-H); 1630 (C=O); 1372 (C-N). H-NMR (400 MHz,
DMSO-d ) : δppm= 0,85 (t, 6H); 1,28 (m, 12); 1,54 (m, 4H); 3,27 (q,
H); 7,82 (d, 2H); 8,76 (d, 2H); 8,84 (d, 2H); 8,90 (t, 2H).
.6.5. N,N'-dibenzyl-2,2'-bipyridine-4,4'-dicarboxamide (L
6
4
2
6
):
-1
White solid, yield 72%. FT-ATR (cm ): 3276 (N-H); 3053 (Ar-H); 2912
2
3,24
localized excitations.
Besides an appropriate basis set
1
(
aliph. C-H); 1640 (C=O); 1354 (C-N). H-NMR (400 MHz, DMSO-d
6
) :
ppm= 4,51 (b, 4H); 7,27 (m, 10H); 7,87 (d, 2H); 8,81 (t, 2H); 8,84 (d,
H); 9,40 (t, 2H).
.6.6. N,N'-2-phenylethyl -2,2'-bipyridine-4,4'-dicarboxamide
combination to CAM-B3LYP method to provide improved accuracy
and tolerable computational performance was applied by using
LALNL2DZ for Ir(III) atoms, 3-21G* for H and F atoms, cc-PVDZ for C
and N atoms and 6-31G* for O atoms. More detailed rationale for
the selection of theory level was given in SI. Percentage molecular
δ
2
2
-1
(
7
L ): White solid, yield 85%. FT-ATR (cm ): 3295 (N-H); 3030-3053
1
(
Ar-H); 2937 (aliph. C-H); 1635 (C=O); 1353 (C-N). H-NMR (400
2
| J. Name., 2012, 00, 1-3
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Pl Ne ae swe Jd oo u nr no at l aod fj Cu sh te mm ai sr tgr iyn s
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DOI: 10.1039/C7NJ04671E
Journal Name
MHz, DMSO-d
ARTICLE
6
) : δppm= 2,87 (t, 4H); 3,52 (q, 4H); 7,26 (m, 10H); NMR (400 MHz, CDCl
3
): δppm= 2,52 (d, 6H); 3,15 (t, 2H); 3,82 (q, 2H);
7
,81 (d, 2H); 8,75 (t, 2H); 8,84 (d, 2H); 9,03 (t, 2H).
.6.7. [Ir(FMeppy) (L )] (1): N,N'-dipropyl-2,2'-bipyridine-4,4'- 7,17 (m, 2H); 7,19 (d, 1H); 7,25 (d, 1H); 7,29 (m, 4H); 7,35 (d, 2H);
dicarboxamide (25 mg, 0.0766 mmol) and [(FMeppy) Ir(ꢀ-Cl)] 7,37 (d, 2H); 7,39 (q, 1H); 7,42 (q, 1H); 7,58 (d, 1H); 7,68 (d, 1H);
38,48 mg, 0.0319 mmol) in
6,17 (m, 1H); 6,60 (m, 1H); 6,73 (m, 2H); 6,80 (m, 1H); 7,08 (m, 1H);
2
2
1
2
2
(
a
mixture of methanol and 7,99 (m, 2H); 8,09 (m, 2H); 9,76 (b, 2H); 10,58 (d, 2H). ESI-MS (m/z)
+
+
dichloromethane (1:2, v/v) were refluxed overnight under argon [M ] 1017.2, [M – L
atmosphere. After cooling, the solution was concentrated and then
7
] 566.2.
O
O
O
O
precipitated with diethyl ether to give the yellow solid with 75%
3
H C
CH
3
HO
OH
EtO
OEt
-1
CrO3
EtOH
yield. FT-ATR (cm ): 3221 (N-H); 3052 (Ar-H); 2872-2962 (aliph. C-
N
N
H SO
N
N
H SO
N
N
1
2
4
2
4
H); 1654 (C=O). H-NMR (400 MHz, CDCl
3
): δppm= 0,98 (t, 6H); 1,81
R
R
NH
HN
(
(
(
(
m, 4H); 2,49 (d, 3H); 2,53 (d, 3H); 3,53 (m, 4H); 6,17 (m, 1H); 6,60
O
O
t, 1H); 6,73 (m, 2H); 6,80 (m, 1H); 7,07 (m, 1H); 7,17 (q, 1H); 7,25
m, 2H); 7,41 (t, 1H); 7,58 (d, 1H); 7,67 (d, 1H); 7,98 (m, 2H); 8,10
O
O
R
O
O
R
NH
EtO
OEt
NH
N
N
N
N
H
2
N R
[(FMeppy)
2
Ir(ꢀ-Cl)]
2
+
N
Ir
N
m, 2H); 9,59 (b, 2H); 10,58 (d, 2H). ESI-MS (m/z) [M + H] 894.4, [M
N
N
N
N
MeOH/CH
2
Cl
2
+
+
H – L
1
] 566.0.
F
F
Complexes (2-7) were prepared using the same procedure for
complex 1 starting from L -L , respectively.
.6.8. [Ir(FMeppy) (L )] (2): Yellow solid, yield 74%. FT-ATR (cm
: 3229 (N-H); 3059 (Ar-H); 2870-2959 (aliph. C-H); 1655 (C=O). H-
NMR (400 MHz, CDCl ): δppm= 0,94 (t, 6H); 1,43 (m, 4H); 1,77 (m,
H); 2,49 (d, 6H); 3,55 (m, 4H); 6,17 (m, 1H); 6,59 (m, 1H); 6,73 (m,
R
R
R
(
1)
2)
(4)
5)
(6)
(7)
2
7
(
(
-
(
3)
2
2
2
1
1
)
3
Scheme 1 The synthetic route for ligands and iridium complexes.
4
2
1
2
H); 6,82 (m, 1H); 7,08 (m, 1H); 7,21 (m, 2H); 7,39 (t, 1H); 7,41 (q,
H); 7,58 (m, 1H); 7,66 (d, 1H); 7,93 (t, 2H); 8,11 (m, 2H); 9,60 (b,
3
. Results and discussion
+
+
H); 10,59 (d, 2H). ESI-MS (m/z) [M + H] 922.1, [M + H – L
.6.9. [Ir(FMeppy) (L )] (3): Yellow solid 89%. FT-ATR (cm ):
211 (N-H); 3059 (Ar-H); 2870-2953 (aliph. C-H); 1660 (C=O). H- The synthetic strategy for the preparation of ligands and iridium
): δppm= 0,88 (t, 6H); 1,37 (s, 8H); 1,79 (t, 4H); complexes is shown in Scheme 1. Simple method was used for the
,49 (d, 3H); 3,54 (d, 3H); 3,55 (q, 4H); 6,16 (m, 1H); 6,59 (t, 1H); preparation of 2,2'-bipyridine-4,4'-dicarboxamide derivatives
,73 (m, 2H); 6,81 (m, 1H); 7,08 (m, 1H); 7,17 (q, 1H); 7,24 (m, 2H); starting from 4,4’-dimethyl-2,2’-bipyridine that described in
2
] 566.2.
-1
3.1. Synthesis and characterization
2
2
3
1
3
NMR (400 MHz, CDCl
3
2
6
7
9
1
7,18,20
,41 (m, 1H); 7,58 (d, 1H); 7,67 (d, 1H); 7,97 (m, 2H); 8,09 (m, 2H); literature.
4,4’-dimethyl-2,2’-bipyridine was oxidized to 4,4’-
+
,63 (b, 2H); 10,57 (d, 2H). ESI-MS (m/z) [M + H] 950.4, [M + H – dicarboxy-2,2’-bipyridine which was converted into 4,4’-
+
L
3
] 566.2.
.6.10. [Ir(FMeppy)
225 (N-H); 3055 (Ar-H); 2856-2927 (aliph. C-H); 1653 (C=O). H- diethoxycarbonyl-2,2’-bipyridine and aliphatic amines with 70-90%
): δppm= 0,86 (t, 6H); 1,30 (m, 8H); 1,78 (m, yield. The reactions of 2,2'-bipyridine-4,4'-dicarboxamide
H); 2,48 (d, 3H); 3,53 (d, 3H); 3,55 (m,4H); 6,16 (m, 1H); 6,59 (t, derivatives were performed in the absence of a solvent with higher
diethoxycarbonyl-2,2’-bipyridine.2,2'-bipyridine-4,4'-dicarboxamide
-
1
2
2 4
(L )] (4): Yellow solid 86%. FT-ATR (cm ): derivatives were synthesized by the reaction of 4,4’-
1
3
NMR (400 MHz, CDCl
3
4
1
2
2
–
2
6
H); 6,72 (m, 2H); 6,80 (m, 1H); 7,07 (m, 1H); 7,18 (q, 1H); 7,24 (m, yield, easy purification and less waste than with solvent. The
H); 7,41 (t, 1H); 7,58 (d, 1H); 7,67 (d, 1H); 7,98 (m, 2H); 8,09 (m, corresponding ligands (L -L ) were used in the complexation
1
7
+
H); 9,60 (b, 2H); 10,57 (d, 2H). ESI-MS (m/z) [M + H] 978.2, [M + H reactions with [(FMeppy) Ir(ꢀ-Cl)] in a mixture of methanol and
2
2
+
L
4
] 566.2.
.6.11. [Ir(FMeppy)
225 (N-H); 3055 (Ar-H); 2856-2927 (aliph. C-H); 1653 (C=O). H-
dichloromethane to give molecules (1-7) which lead to good
-
1
2
2 5
(L )] (5): Yellow solid 56%. FT-ATR (cm ): solubility in common organic solvents.
1
3
The structures of the prepared compounds were confirmed by a
1
NMR (400 MHz, CDCl
3
): δppm= 0,85 (t, 6H); 1,33 (m, 20H); 1,78 (m, combination of FTIR, H NMR and mass spectroscopies. The FTIR
4H); 2,48 (d, 3H); 3,53 (d, 3H); 3,54 (q, 4H); 6,16 (m, 1H); 6,59 (m, spectra of ligands (1-7) exhibit characteristic vibration bands of N–H
1
H); 6,72 (m, 2H); 6,80 (m, 1H); 7,07 (m, 1H); 7,17 (m, 1H); 7,26 (m, and C=O units of amide groups appeared in the range of 3276 to
-1
-1
2H); 7,41 (m, 1H); 7,58 (d, 1H); 7,66 (d, 1H); 7,96 (m, 2H); 8,09 (t, 3305 cm and 1630 to 1640 cm , respectively. The C-H stretching
+
2H); 9,61 (b, 2H); 10,59 (d, 2H). ESI-MS (m/z) [M + H] 1034.4, [M + bands of the alkyl chains and aromatic rings of ligands are appeared
+
-1
-1
H – L
5
] 566.2.
between 2954-2867 cm and 3030-3065 cm , respectively. Upon
)] (6): Yellow solid 94%. FT-ATR (cm ): complexation, the red shifting of N–H bands and the blue shifting of
-1
2
.6.12. [Ir(FMeppy)
2
(L
6
1
3229 (N-H); 3060 (Ar-H); 2927 (aliph. C-H); 1661 (C=O). H-NMR C=O bands of 2,2'-bipyridine-4,4'-dicarboxamide ligands are
1
3
1
(400 MHz, CDCl ): δppm= 2,51 (d, 6H); 4,72 (d, 4H); 6,16 (m, 1H); observed in complexes (1-7). In the H NMR spectra of ligands (L -
6
7
7
,59 (m, 1H); 6,72 (m, 2H); 6,78 (m, 1H); 7,06 (m, 1H); 7,14 (m, 1H); L ), the amide N-H signal as a triplet and N-CH proton signals as
5
2
,21 (m, 3H); 7,31 (t, 4H); 7,38 (m, 2H); 7,56 (s, 2H); 7,58 (s, 2H); quartet are observed at 8.90 ppm and 3.27 ppm, respectively (Fig.
2
7
,66 (d, 2H); 7,96 (m, 2H); 8,07 (m, 2H); 10,24 (b, 2H); 10,62 (d, 2H). 1a). The peaks at 4.51 ppm and 7.27 ppm are appeared due to the
+
+
ESI-MS (m/z) [M] 989.3, [M – L
.6.13. [Ir(FMeppy) (L )] (7): Yellow solid 52%. FT-ATR (cm ): In case of L ligand, CH protons adjacent to the amide N-H and
230 (N-H); 3058 (Ar-H); 2861-2928 (aliph. C-H); 1662 (C=O). H- phenyl groups resonates at 3.52 ppm and 2.88 ppm, respectively.
6
] 566.1.
2 6
CH and phenyl signals of benzyl groups in the spectrum of L ligand.
-1
2
2
7
7
2
1
3
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1
1
Fig. 1 a) H NMR spectrum of L
1
ligand in DMSO-d
6
b) H NMR spectrum of complex 1 in CDCl
3
c) ESI mass spectra of complex 1 dissolved in
acetonitrile.
1
In the H NMR spectra of iridium complexes (Fig. 1b), the ratios 3.2. Absorption and emission studies
of aromatic and aliphatic resonance peaks indicate the presence of
The absorption spectra of the complexes (1-7) are shown in Fig. 2
two 2-phenylpyridine and corresponding bipyridine ligands. The
two peaks appeared between 2.48 and 3.54 ppm originate from the
methyl substituent of 2-phenylpyridine. The amide N-H signals of
the complexes shifted to downfield compared to free ligands. The
formation of complexes were further verified by ESI-mass data. In
the ESI-mass spectra, the complexes gave the parent molecular ion
and corresponding data are given in Table 1. In the UV region, the
intense bands (285 nm-335 nm) are observed due to the π-π*
1
ligand centered charge transfer ( LC) transitions of 2-(3-
fluorophenyl)-4-methylpyridine and bipyridine ligands. The
absorption bands in the range of 357 nm to 386 nm are attributed
to spin-allowed singlet-singlet metal-to-ligand charge-transfer
+
+
[
M +H] for complexes (1-5) and [M] for complexes (6-7) which
followed by the loss of corresponding 2,2'-bipyridine-4,4'-
dicarboxamide ligands (L -L ) (Fig. 1c).
1
(
MLCT). The weaker absorption bands around 480 nm are
associated with spin-forbidden singlet-triplet metal-to-ligand
3
1
7
charge-transfer ( MLCT) transitions.
-
5
-
5
Fig. 3 PL spectra of 5x10 M solutions of the iridium complexes in
Fig. 2 UV-Vis absorption spectra of 5x10 M solutions of the iridium
complexes in different solvents: dichloromethane, chlorobenzene,
toluene.
different solvents: dichloromethane, chlorobenzene, toluene.
4
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Table 1 Absorption and emission data of the iridium complexes (1-7)
ꢂꢄꢅ
ꢇꢁ
Complex
Solvent
ꢀ
ꢆ
(nm)
ꢀ ꢆ
ꢁꢂꢃ
Φem
ꢁ
ꢂꢃ
4
-1
-1
ꢈꢉꢁꢊ
(ε/10 M .cm )
1
CH
2
Cl
2
333 (2.02) 362 (1.53) 384 (1.27) 481 (0.15)
604
575
548
603
574
548
604
574
548
602
572
548
603
570
548
610
583
552
608
580
550
0.71
0.72
0.82
0.50
0.74
0.78
0.62
0.75
0.74
0.60
0.65
0.68
0.57
0.70
0.68
0.41
0.68
0.76
0.44
0.73
0.75
Chlorobenzene
Toluene
CH Cl
2 2
289 (3.73) 332 (1.98) 360 (1.09) 383 (0.90) 473 (0.11)
286(0.91) 335 (0.48) 358 (0.28) 381 (0.25) 480 (0.04)
334 (1.37) 362 (1.14) 386 (0.94) 489 (0.12)
289 (3.73) 332 (1.97) 361 (1.08) 385 (0.82) 474 (0.11)
283 (2.01) 337 (1.01) 357 (0.59) 381 (0.45) 485 (0.06)
334 (1.22) 362 (1.04) 386 (0.84) 480 (0.10)
289 (4.05) 333(2.15) 361 (1.17) 385 (0.98) 477 (0.11)
285 (3.89) 334(2.04) 358 (1.18) 381 (0.91) 481 (0.10)
333 (1.22) 362 (1.03) 384 (0.80) 478 (0.13)
289 (3.82) 333 (2.00) 361 (1.10) 385 (0.91) 476 (0.10)
286 (4.10) 335 (2.26) 359 (1.28) 380 (1.00) 479 (0.16)
333 (1.78) 362 (1.35) 383 (1.14) 478 (0.13)
289 (4.81) 332 (2.68) 360 (1.46) 385 (1.22) 477 (0.14)
285 (3.43) 335(1.83) 358 (1.03) 381 (0.84) 480 (0.11)
333 (1.90) 363 (1.40) 385 (1.22) 485 (0.13)
288 (2.11) 330 (1.10) 363 (0.63) 387 (0.53) 478 (0.06)
284 (2.50) 335 (1.30) 358 (0.76) 381 (0.58) 482 (0.07)
333 (1.65) 363 (1.30) 385 (1.00) 483 (0.11)
2
3
4
5
6
7
Chlorobenzene
Toluene
CH Cl
2 2
Chlorobenzene
Toluene
2 2
CH Cl
Chlorobenzene
Toluene
2 2
CH Cl
Chlorobenzene
Toluene
CH Cl
2 2
Chlorobenzene
Toluene
CH Cl
2 2
Chlorobenzene
Toluene
290 (4.77) 333 (2.61) 362 (1.45) 386 (1.21) 482 (0.13)
286 (4.29) 335 (2.37) 359 (1.35) 381 (1.05) 479 (0.11)
Fig. 3 exhibits the PL spectra of the complexes (1-7) in different
solvents at room temperature. The complexes (1-5) with alkyl side
chains display similar PL spectral features which give orange-red
emission bands at around 604 nm in dichloromethane. The
emission red-shifting of 6 nm in complexes (6-7) are observed in the
the presence of benzyl and 2-phenylethyl groups. All the complexes
show tunable photoluminescence wavelengths depending on
solvent polarity in the range of 548 nm to 610 nm where the
emission colour can change from green to orange-red (Fig. 4). The
PL spectra of the complexes displays blue-shifted emission with the
decreasing solvent polarities (toluene
<
chlorobenzene
<
dichloromethane) (Table 1). This can be attributed to the less
interaction between excited molecules and solvents which can
destabilize the excited state of the complexes and increase energy
-
5
28,29
Fig. 4 PL spectra of 5x10 M solutions of the complex 1 in different
content
important for the PL spectra of synthesized complexes. The PL
quantum yields ( PL) of complexes are calculated according to the
literature using fac-Ir(bpy) as the reference material ( PL = 0.4 in
This indicates that the polarity of the solvents are
solvents: dichloromethane, chlorobenzene, toluene.
Φ
2
8
The HOMO energy levels of the complexes were calculated by
3
Φ
3
1
3
0
using the maximum of first oxidation potential. Ferrocene was
toluene). The PL quantum yields of the complexes (1-7) are found
between 0.41 and 0.75. The synthesized complexes (1-7) show high
quantum yield due to the change of dipole moment of the amide
groups of 2,2'-bipyridine-4,4'-dicarboxamide ligands upon
+
used as an internal standard (0.46 V vs. Ag/ Ag ). The band gaps (Eg)
of complexes were determined from the band edge of absorption
spectra of the complexes. The LUMO energy levels of the
3
1
1
2,13
complexes were obtained from the equation (
The calculated HOMO and LUMO energy levels of the complexes (1-
) are in the range of -5.51-(-5.60) eV and -3.37-(-3.40) eV,
The cyclic voltammograms of the complexes (1-7) are shown in Fig. respectively. The band gaps of the complexes are between 2.14 eV
and the corresponding data are given in Table 2. The cyclic and 2.22 eV. The energy levels and band gaps of the complexes can
LUMO HOMO
E = E + Eg).
electronic excitation.
3
.3. Electrochemical data
7
5
voltammograms of the complexes exhibit two oxidation peaks at be appropriate to be applied as a dopant in commonly used host
around 1.25 V and 1.60 V which are assigned to the iridium metal materials, e.g. poly(N-vinyl carbazole) (PVK), for OLED device
1
6,32
and the phenyl fragment of 2-phenylpyridine, respectively.
structure.
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6
are given in Fig. 7. Root mean squared (RMS) overlays of the S
0
and T
1
optimized geometries are superimposingly given in Fig. 8.
Some important geometrical parameters of S
are listed in Table 3.
0 1
and T states of 1 and
6
Fig.5 Cyclic voltammogram of the complexes (1, 3, 5, 7) measured in
-1
3
CH CN solutions with scan speed of 100 mVs .
Fig. 7 S optimized structures of 1 and 6 (hydrogens were ommited
0
for clarity).
Table 2 The electrochemical data of the complexes (1-7) in CH CN
3
Table 3 Important optimized structural parameters of 1 and 6
Complex
E
ox1
E
(V)
ox2
HOMO
(eV)
E
(eV)
g
LUMO
(eV)
(
V)
1
6
1
2
3
4
5
6
7
1.24 1.62
1.25 1.64
1.25 1.62
1.18 1.58
1.17 1.56
1.24 1.60
1.26 1.56
-5.58
-5.59
-5.59
-5.52
-5.51
-5.58
-5.60
2.19
-3.39
-3.40
-3.40
-3.37
-3.37
-3.39
-3.38
S
0
T
1
S
0
T
1
Parameter
Ir1ꢀN1
2.19
2.19
2.15
2.14
2.19
2.22
2.162
2.075
2.034
76.40
2.132
2.068
2.049
78.34
2.162
2.075
2.034
76.41
2.133
2.068
2.049
78.34
Ir1ꢀN2
Ir1ꢀC1
N1ꢀIr1ꢀN1
N2ꢀIr1ꢀN2
C1ꢀIr1ꢀC1
C1ꢀIr1ꢀN2
172.85 174.67 172.91 174.78
89.08
80.20
86.89
80.08
89.14
80.20
86.90
80.07
3
.4. Ground and excited state structures
The details of overall calculations executed in stepwise manner are
given in section 2 while their routes are schematized in Fig. 6. All
the complexes display similar structural features based both on the
experimental and calculated data, the S , and T structures 1 and 6
0
1
were only examined. S optimized structures of 1 and
0
Fig. 8 Superimpositions of S
0
(blue) and T
1
excited state (red)
geometries of 1 and 6.
The values in Table 3 are comparable in magnitude with related
3
,33,34
structures reported in the literature.
At the instant of
excitation to the lowest lying T state, small structural distortions
1
that are accompanied by lengthening of C1-Ir1 bonds and
shortening of N1-Ir1 and N2-Ir2 bonds were observed. RMS errors
Fig. 6 The associations of overall computations performed in this for the overlays of S
study.
0.2658 Å respectively and denote to low structural change during
→T transition. S state molecular orbital (MO) isodensity plots
0 1
and T geometries of 1 and 6 are 0.2315 Å and
S
0
1
0
6
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for 1 and 6, together with gap values and some important higher 3.5. Absorption, emission profiles and TD-DFT calculations
LUMO+3) and lower (HOMO-1) lying molecular orbitals, are
For throughout quantitative assessment of observed
(
depicted in Fig. 9. In both complexes, HOMO consists of the photophysical and photochemical phenomena in Ir(III) complexes
contributions from Ir1 and phenyl moieties of phpy ligands while TD-DFT computations with density hybrid functionals are most
3
5,36
LUMO almost completely resides at bpy ligands. The same trend is commonly used methodologies.
With an accuracy of their
not valid in cases of HOMO-1 and LUMO+3. HOMO-1 locates results within the limit of 0.1 eV and very low computational costs,
predominantly at phenyl moieties of phpy ligands like HOMO but TD-DFT methods relative to multi-configurational ones provides
LUMO+3 locates mainly at pyridyl and partly at phenyl moieties of large facilities to probe both ground and excited state properties by
the same ligand in contrast to LUMO. Percentage molecular optimizing both states. TD-DFT is nowadays very promising tool to
contributions of central atoms and ligands to frontier molecular manipulate characters of complicated excited state charge transfer
orbitals (FMOs) are reported in Table 4. The lengthening of HOMO- manifolds that are mainly responsible for the efficiency and ideal
associated Ir1-C1 bond upon moving the electron away from HOMO light emission in optically active Ir(III) complexes.
by excitation suggests that HOMO is of bonding character since it
In this context, we subjected complex 1 to several TD-DFT
seems, with an in-depth investigation of Fig. 7, populated mostly on procedures considering the overall processes including all
C1. Interestingly, the shortening of LUMO-associated Ir1-N1 bond transitions. The diagram depicted in Fig. 10 was developed for
upon moving the electron into LUMO also denotes to a bonding appropriately interpreting both vertical and adiabatic transitions
character of LUMO. The slightly shortening of Ir1-N2 bond seems responsible for the absorption, emission and non-radiative
driven by lengthening of Ir1-C1 bond residing in the same chelate relaxation processes as well. At the diagram below, the first vertical
ring.
excitation energy represents the AS transitions to the higher
vibrational levels of S1 state. The transition to the higher
vibrational level of first triplet excited state also corresponds to
R1+R3) difference. TD calculations carried out at S and T
A
T
A
S
-
(
1
1
geometries give the energies of fluorescence and phosphorescence
transitions respectively. Separately subtraction of the total
electronic energies of S1 and T1 excited state optimized geometries
from that of optimized
S
0
state geometry (excluding ZPE
corrections) give A.T1 and A. T2 energies for
transitions respectively.
1 0 1 0
S →S and T →S
For clarity, the model diagram in Fig. 10 is unproportionally
constructed so as to display the transitions qualitatively. The P
transition actually occurs vertically into vibrational state of S
as though it comes across outside the curve in the diagram. The
similar case also holds for transition since it actually occurs
vertically upto highest vibronic T state. The calculations of the
0
curve
A
T
1
emission energies referring to above diagram were made based on
the situation that the effective overlaps of vibrational
wavefunctions (Franck Condon integrals) for radiative/nonradiative
-
3
Fig. 9 Isodensity plots, with 0.03 eÅ isovalues, of some selected
MOs in 1 and 6 together with gap values.
relaxations between lowest vibronic S
1 1
or T levels and various
vibrational levels of S state are provided.
0
Table 4 Percentage MO contributions of atoms and ligands to FMOs in 1 and 6.
Comp.
MO
H
ꢀ7.819
37.6
4.8
Hꢀ1
ꢀ8.35
3.0
Hꢀ2
Hꢀ3
L
L+1
L+2
L+3
E (eV)
Ir1
ꢀ8.753 ꢀ8.795 ꢀ5.326 ꢀ4.487 ꢀ4.444 ꢀ4.193
41.8
3.4
31.8
4.5
6.2
84.1
2.1
2.3
85.1
2.5
1.8
80.0
1.9
6.9
2.3
1
bpy
2.2
phpy
E (eV)
Ir1
28.7
47.3
27.0
31.2
45.2
ꢀ7.807 ꢀ8.339 ꢀ8.741 ꢀ8.760 ꢀ5.324 ꢀ4.485 ꢀ4.434 ꢀ4.176
37.6
4.8
3.0
2.2
41.4
3.4
0.1
3.1
0.0
6.9
83.7
2.0
7.0
83.5
2.4
4.4
79.5
1.8
6.9
2.2
6
bpy
phpy
28.7
47.3
27.2
45.2
H, HOMO; Hꢀ1, HOMOꢀ1; etc., L, LUMO; Lꢀ1 LUMOꢀ1, etc.
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Table 5 Calculated spectral parameters of 1 together with observed transition wavelengths
λ
nm
λ
nm
( f )
MO
Composition
eV
(calc.)
Transition
Major character
λ
ev
(
exp.) (calc.) (calc.)
3
H→L+3(19%)
Hꢀ1→L+4(14%)
H→L(10%)
MLLCT d/π(phpy)→π*(phpy)
0.305
0.27
0.22
0.37
0.36
0.62
0.68
0.64
0.44
3
S
0
→T
1
480
474
471
ꢀ
ꢀ
ILT π(phpy)→π*(phpy)
2.62
2.63
3
MLLCT d/π(phpy)→π*(bpy)
3
Hꢀ1→L+3(27%)
H→L+4(26%)
H→L(75%)
ILT π(phpy)→π*(phpy)
S
0
→T
2
3
ꢀ
3
MLLCT d/π(phpy)→π*(phpy)
ꢀ
ꢀ
3
S
0
S
0
S
0
S
0
→T
451
450
348
332
MLLCT
2.75
2.76
3.56
3.74
1
→S
1
ꢀ
0.0002 H→L(93%)
0.14 H→L+3(81%)
0.057 Hꢀ1→L(38%)
MLLCT
1
→S
n
n
358
335
MLLCT
1
→S
LLCT π(phpy)→π*(bpy)
The calculated 474 nm transition, which is assigned to 481 nm
observed one as seen in Table 5, composed of the contributions
from H→L, H→L+3 and H-1→L+4 components that are designated
3
3
3
as MLLCT, ILT and MLLCT manifolds respectively. The
corresponding excitation is associated with the sum of R2+P+R4 A -
(
S
(
R1+R3)), in Fig. 10. The calculated S0→S1 transition wavelength is
4
50 nm with an almost single H→L component indicaꢀng a single
1
excitation of MLLCT character. From the above diagram, S0→S1
excitation equals directly to AS. But corresponding very low
oscillator strength (0.0002) denotes to a very low transition
probability even then it is spin-allowed. 451 nm calculated
0 3
S →T
transition on which H→L component is dominant was not observed
owing probably to be shielded by the tails of more intense and
ligand based singlet transitions. The higher energy bands observed
above 335 nm correspond to intraligand transitions.
In Fig. 3 (toluene), 1 and 6 exhibit strong emission with 548 nm
and 552 nm maxima respectively. The energy of 548 nm emission,
associated with
P
in Fig. 10, was underestimated to be 521 nm by
optimized structure. The
Fig. 10 Diagram showing the transitions responsible for absorption,
TD calculation performed at
T
1
emission and non-radiative relaxation processes (AT: triplet
underestimation with a difference of 27 nm is not ignorable but can
be approved reasonable considering that the actual reference
geometry such as X-ray structure was not available for initializing
S
absorption, A : singlet absorption, A.T: adiabatic transition, F:
fluorescence, P: phosphorescence and R: non-radiative relaxation.
Dashed lines emphasize experimentally not observed transitions).
the S
state optimization (Fig. 6).
The calculated →S
associated with in Fig. 10 while the corresponding excitation
energy is 450 nm (Table 5) and associated with . The total
electronic energies of S , T and S states from SPE calculations at
0
optimization which is the precursor geometry for excited
Owing to high spectral data similarities of 1 and 2, calculated
absorption and emission data of 1 were only represented. In
absorption spectra of 1 in toluene, very low intensity band tail lying
onto 450-500 nm region is slightly distinctable in Fig. 2. This large
S
1
0
singlet emission energy is 509 nm and
F
A
S
0
1
1
band which is maximized at 481 nm and assigned to be originated the optimized structures are already known. Then by summing up
from spin-forbidden singlet-triplet transition is also fairly the data obtained from all SPE and TD calculations, all the
reproduced by TD calculation only with a small underestimation of transitions at the diagram in Fig. 10 can be computed and their
7
nm.
Important calculated transition wavelengths together with their
designations, characters, oscillator strengths, and eigenvalues (λev
as well as experimental transition wavelengths are listed in Table 5.
relationships are compiled in Table 6.
At the diagram in Fig. 10, we only interested in the calculations
of excitation and emission processes. If desired, energies related to
all relaxation processes (R) which are not experimentally
measurable can also be computed using the equations in Table 6.
)
8
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In order to interpret and visualize the population density of coupling at the T
1
state. Even at first glance, it is easily understood
S
0
→T and →S transitions, natural transition orbital (NTO) from Fig. 11 that both the hole and particle distributions of T →S
1
T
1
0
1
0
analyses representing the orbital pairs of maximum eigenvalues in transition are extremely concentrated on metal center and suggest
terms of single particle transition density matrix were carried out at a metal localized triplet emission in contrast to the results from the
S
0
and T
occupied NTO (HOTO) and the lowest unoccupied NTO (LUTO) for measured ΦPL values (0.71 and 0.41 for 1 and 6 respectively) with
corresponding states are given in Fig. 11. calculated oscillator strengths ( ) is not possible since all values
For →T , a LLCT transition with hole distribution of mainly on are zero for triplet transitions on account of the neglect of strong
phenyl moieties of phpy ligand and particle distributions of mainly heavy metal spin-orbit mixing by this classical TD calculation. On the
on bpy ligand is assigned. The low eigenvalue (λ) for →T NTO other hand, localization of →S transition is somewhat associated
pairs is an expected result for this spin-forbidden transition and with ΦPL and thence strong localization of NTO pairs of →S with
1
states. Hole and particle distributions of the highest interpretation of ground state FMOs. Association of experimentally
f
f
S
0
1
S
0
1
T
1
0
T
1
0
consistent with the observed very weak band tail slightly extending λ=0.68 on metal center correlates well with the measured ΦPL
into visible region in the absorption spectra.
.
3
.6. Computations for electrochemical studies
Despite the use of various popular pure and hybrid density
functionals including LSDA, LYP, M06L, B3P86, M062X, the overall
data obtained from PCM-optimized structures did not successfully
revealed the experimental trends. The experimentally estimated
energies of HOMO, LUMO and gap together with calculated ones
are reported in Table 7.
Table 6 Equations giving transition energies and energy differences
for the overall processes including absorption, emission, and non-
radiative relaxations at the diagram in Figure 10
Transition/∆E
Energy equivalent
Table 7 Calculated and experimental electrochemical parameters of
1
using CAMꢀB3LYP functional
S
S
0
→S
1
A
A
S
Quantity
S0
SPE
ꢀ9.14
ꢀ4.23
ꢀ2.91
S0(PCM) SPEPCM
Expt.
0
→T
1
T
2 4
or R +P+R
HOMO (ev)
LUMO(ev)
ꢀ8.05
ꢀ5.54
ꢀ5.94
ꢀ7.14
ꢀ1.80
ꢀ5.34
ꢀ5.58
ꢀ3.39
ꢀ2.19
1.24
E(T ꢀE(S )
P+R or A.T2
1
)
0
4
ꢀ3.03
ꢀ4.91
E(S ꢀE(S )
AꢀR or A.T1
1
)
0
1
∆E
HOMOꢀ
LUMO(ev)
ꢀ2.51
S1→S0
T1→S0
F or A.T1ꢀR4
P or A.T2ꢀR4
E
ox1(ev)
5.71
S
S
0
: the values obtained directly from gas phase optimization,
0(PCM): the values obtained from pcmꢀoptimization and, SPE: the
S
1→
T
1(isc)
1 2 3
E(S1)ꢀE(T ) or R +R
values obtained from SPE calculation at the corresponding
optimized geometry
E: Total electronic energy of corresponding state,
isc: intersystem crossing
The calculations through
N and N-1 optimized structures
unfortunately overestimated the experimental oxidation potentials.
Although the calculated values in Table 5 do not correlate well with
the experimental ones, implementing PCM to the calculation seems
improved the values from gas-phase calculation to some extent. On
the other hand,
S0(PCM) data are in best accordance with
experimental values.
4
. Conclusions
We reported the synthesis, characterization, photophysical and
electrochemical properties of new iridium complexes containing 2-
3-fluorophenyl)-4-methylpyridine and 2,2'-bipyridine-4,4'-
(
dicarboxamide derivatives. The effects of solvents on
photoluminescent properties of the complexes have been
investigated. The emission colour is tuned from green to orange-
red depending on solvent polarity in the presence of 2,2'-bipyridine
0
and -4,4'-dicarboxamide ligands despite the similarities in emissive
Fig. 11 Hole and particle distributions of HOTO and LUTO for S
T
1
states.
properties of the complexes. The experimental trends among the
1 0
However, for T →S , reasonably higher λ=0.68 value denotes to prepared complexes demonstrates that the change of peripheral
becoming spin-allowed transition as a result of strong spin-orbit alkylamide groups on 2,2'-bipyridine moieties do not effects the gap
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ARTICLE
Journal Name
values, redox potentials and emission wavelengths reasonably. On
the other hand, these groups in the presence of polar solvents seem
perturbs the excited state by stabilization which results in lower gap
values and hence higher wavelength emission compared to related
structures previously reported. The computational data from DFT
Applications in Sensing and Imaging, ed. A. P. Demchenko
and O. S. Wolfbeis, Chapter 1, Springer: Heidelberg, 2011,
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disadvantage arising from the use of optimized structures obtained
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The simple calculations by using this diagram estimated the
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observed excitation and emission energies within the acceptable
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of 0.22 for
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→
T1 transition somewhat resembles ground state
→S
HOMO-LUMO transition of MLLCT character while these for
T
1
0
transition with an higher amplitude of 0.68 seems populated mostly
on metal center and suggests a metal-localized emission denoting
to significantly strong heavy-metal spin-orbit mixing. Consequently,
the overall data obtained from experimental and computational
studies suggest that these molecules are potential candidates as
dopant in OLED applications.
2
2 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We acknowledge Pamukkale University for the project support fund
(Project Number: 2013FBE027).
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DOI: 10.1039/C7NJ04671E
Table of Content
The photophysical properties of new iridium complexes have been investigated depending on
various solvents and substituents and DFT/TD-DFT studies have supported observed optical
data.