Herein, we have synthesized a series of 2',6'-difluoro-2,3'-bipyridine cyclometalating ligands by... more Herein, we have synthesized a series of 2',6'-difluoro-2,3'-bipyridine cyclometalating ligands by
substituting electron-withdrawing (–CHO, –CF3, and –CN) and electron-donating (–OMe and –NMe2)
groups at the 4' position of the pyridyl moiety and utilized them for the construction of five new
iridium(III) complexes (Ir1–Ir5) in the presence of picolinate as an ancillary ligand. The photophysical
properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (–CN) group containing the iridium(III) compound (Ir3)
exhibits highly efficient genuine green phosphorescence (lmax = 508 nm) at room temperature
in solution and in thin film, with an excellent quantum efficiency (FPL) of 0.90 and 0.98, respectively.
On the other hand, the –CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission
(lmax = 468 nm) with a promising quantum efficiency (FPL = 0.88 and 0.84 in solution and in thin film,
respectively). The –CHO substituted iridium(III) complex (Ir1) showed greenish-yellow emission (lmax =
542 nm). Most importantly, the strong electron-donating –NMe2 substituted iridium(III) complex (Ir5)
gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (lmax =
520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum
efficiency, especially in thin-film noted in the case of the –OMe substituted iridium(III) complex (Ir4).
Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have
been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to
obtain information about the absorption and emission processes and to gain deeper insights into the
photophysical properties. The combinations of a smaller DES
1–T1 and higher contribution of 3MLCT in the
emission process result in the higher quantum yields and lifetime values for complexes Ir1–Ir3. Multilayered Phosphorescent Organic Light Emitting Diodes (PhOLEDs) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and their elecroluminescence properties were evaluated. Compound Ir4 at
a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7%, in the
nonoptimized device, and a power efficiency of 5.8 lm W1, together with a true-blue chromacity
CIE
x,y = 0.15, 0.17 recorded at the maximum brightness of 33 180 cd m2
We demonstrate a spatially uniform enhancement of individual quantum dot (QD) fluorescence emissi... more We demonstrate a spatially uniform enhancement of individual quantum dot (QD) fluorescence emission using plasmonic grating decouplers on thin gold or silver films. Individual QDs are deposited within the grating in a controlled way to investigate the position dependency on both the radiation pattern and emission enhancement. We also describe the optimization of the grating decoupler. We achieve a fluorescence enhancement ~3 times higher than using flat plasmon film, for any QD position in the grating.
We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fabricated u... more We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fabricated using a poly(methylmethacrylate) (PMMA) and lithium fluoride (LiF) composite dielectric. Increasing the concentration of LiF in the composite dielectric reduces the operating gate voltages significantly from 10 V to 1 V required leading to a decrease in resistance. Electron and hole mobility of 350 and 310 cm2/Vs at VD = -5 V are obtained for graphene FEDs with 10 % LiF concentration in the composite. Using composite dielectric also enabled excellent performance on flexible substrates without any significant change in mobility and resistance. Flexible FEDs with only 5 % and 12 % variation in mobility for 300 and 750 bending are obtained.
Energetic disorder in disordered organic solids has been found to alter their physical parameters... more Energetic disorder in disordered organic solids has been found to alter their physical parameters. Here, we have demonstrated, by means of Monte-Carlo simulation and experiments, that the electroluminescence (EL) spectrum is dependent on energetic disorder. This dependence has been attributed to the charge carrier relaxation during hopping process. The dependence of EL spectrum on energetic disorder makes it temperature dependent and temperature dependence has been found to vary with energetic disorder in a variety of materials. The simulation has been performed by taking the relaxation of charge carriers via transport energy in the Gaussian density of states. An analytical equation was established for spectral shift as a function of transport energy.
ABSTRACT Energetic disorder in disordered organic solids has been found to alter their physical p... more ABSTRACT Energetic disorder in disordered organic solids has been found to alter their physical parameters. Here, we have demonstrated, by means of Monte-Carlo simulation and experiments, that the electroluminescence (EL) spectrum is dependent on energetic disorder. This dependence has been attributed to the charge carrier relaxation during hopping process. The dependence of EL spectrum on energetic disorder makes it temperature dependent and temperature dependence has been found to vary with energetic disorder in a variety of materials. The simulation has been performed by taking the relaxation of charge carriers via transport energy in the Gaussian density of states. An analytical equation was established for spectral shift as a function of transport energy.
ABSTRACT We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fab... more ABSTRACT We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fabricated using a poly(methylmethacrylate) (PMMA) and lithium fluoride (LiF) composite dielectric. Increasing the concentration of LiF in the composite dielectric reduces the operating gate voltages significantly from 10 V to 1 V required leading to a decrease in resistance. Electron and hole mobility of 350 and 310 cm2/Vs at VD = -5 V are obtained for graphene FEDs with 10 % LiF concentration in the composite. Using composite dielectric also enabled excellent performance on flexible substrates without any significant change in mobility and resistance. Flexible FEDs with only 5 % and 12 % variation in mobility for 300 and 750 bending are obtained.
Electrical transport of pure and tetrafluoro-tetracyano-quinodimethane doped 4, 4′, 4 ″-tris (N-3... more Electrical transport of pure and tetrafluoro-tetracyano-quinodimethane doped 4, 4′, 4 ″-tris (N-3-methylphenyl-N-phenylamino) triphenylamine (m-MTDATA) films have been studied at various temperatures and doping concentrations. Pure films show space charge limited conduction with field and temperature dependent mobility. The J–V characteristics of doped m-MTDATA were ohmic at low voltages due to thermally released carriers from dopant states. At higher voltages the current density increases nonlinearly due to field dependent ...
We study the fluorescence emission from single dye molecules in coplanar plasmonic cavities compo... more We study the fluorescence emission from single dye molecules in coplanar plasmonic cavities composed of a thin gold film surrounded by two in-plane surface plasmon Bragg mirrors. We first discuss the effect of the presence of Bragg mirrors on the radiation diagram of surface plasmon coupled emission. Then, we investigate the role of the planar cavity size by single-molecule fluorescence lifetime imaging. Experimental data are compared to numerical simulations of the decay rates calculated as a function of the molecule orientation and position within the cavity. The creation of new decay channels by coupling to the cavity modes is also discussed. We measure a plasmonic Purcell factor up to five, attributed to the enhancement of the radiative rate.
In a search for blue light emitting multifunctional materials, the electron transport enhancing d... more In a search for blue light emitting multifunctional materials, the electron transport enhancing diphenyl phosphine–oxide (Ph2P[double bond, length as m-dash]O) group has been appended to blue light emitting pyrene derivatives. This design, we observe, leads to highly efficient electron transporting blue-emitters for non-doped organic light emitting devices (OLEDs) with good film formation characteristics. The superior performance is attributed to enhanced charge transport and formation of pyrene excimers assisted by thermally activated delayed fluorescence (TADF) in the device. We report the synthesis and characterization using experimental and computational methods of six such pyrene derivatives. Although three of these derivatives show quenching of luminescence in solvents at higher concentrations, in the thin film invariably all six of them exhibit typical pyrene excimer emission. X-ray crystal analysis reveals π–π stacking and the C–H[cdots, three dots, centered]O interactions in the solid due to the P[double bond, length as m-dash]O group. The measured electron mobilities for all the compounds are higher in comparison to the standard electron transport material, Alq3. Non-doped OLEDs with the pyrene derivatives as emitters (multi-layer configuration) as well as electron transport cum emitters (bilayer configuration) exhibit excellent efficiencies. The derivatives as emitters display a performance with current efficiencies (ηc) in the range 21.1–30.1 cd A−1, power efficiencies (ηp) 11.0–15.76 lm W−1, external quantum efficiencies (EQE) 7.2–9.1% and brightness 28[thin space (1/6-em)]500–42[thin space (1/6-em)]750 cd m−2. In addition, the derivatives as electron transporting emitters demonstrate very good external quantum efficiencies in the range of 3.0–4.0%. These results demonstrate a successful strategy to obtain blue light emitting multifunctional materials for OLED applications.
In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2-phenyl-1... more In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene (OXD-PH, OXD-PTOL and OXD-OTOL). The effect of methyl substitution at ortho (OXD-OTOL) and para position (OXD-PTOL) on the phenyl ring on the electron transport properties was studied and the results were compared with the anthracene derivative without any substitution at the phenyl ring. Electron transport was found to be highly dependent on the methyl substitution and electron mobilities in OXD-PTOL and OXD-OTOL were found to be lower than in OXD-PH. Mobilities were also found to be different for OXD-PTOL and OXD-OTOL, which indicates that the substitution at different places did not have a similar effect on charge transport properties. Thickness dependent trap states were observed for all three molecules with thickness dependent electron mobilities. Electron mobility was found to increase in all three molecules with the decrease in thickness, which favors their use for organic electronic devices and all three molecules had a better electron transport in comparison to Alq3. These results were explained by the DFT calculation which showed a dihedral structure. The dihedral angle was found to reduce in the anionic form of these molecules. Therefore, these molecules are likely to favor a proper stacking in the solid state form.
Color stability in multi-emissive layer organic light emitting devices (Me-OLEDs) has been invest... more Color stability in multi-emissive layer organic light emitting devices (Me-OLEDs) has been investigated. Me-OLEDs were based on multiple emitters with a common host CBP doped with three dopants, BCzVBi, Ir (ppy) 3 and Ir (btp) 2acac for blue, green and red emission. A major variation in CIE coordinates were found from (0.312, 0.294) to (0.236, 0.267) with increase in voltage from 6 to 9V. This coordinate shift in Me-OLEDs has been attributed to the shifting of recombination zone with increase in voltage.
Abstract Nanostructures of indium tin oxide (NSITO) deposited using glancing angle deposition (GL... more Abstract Nanostructures of indium tin oxide (NSITO) deposited using glancing angle deposition (GLAD) technique are used to enhance the outcoupling efficiency of blue and green OLEDs. The enhancement was found to be angle independent. The efficiency of device has increased by about 2.1 times by the use of NSITO at glass/air interface and ITO/glass interface. Similarly nano-phosphor particles were used to recover the glass modes by depositing them on the backside of the substrates.
abstract White organic light emitting diodes were fabricated using two zinc complexes bis (2-(2-h... more abstract White organic light emitting diodes were fabricated using two zinc complexes bis (2-(2-hydroxyphenyl) benzoxazolato) zinc (II)[Zn (HPB)< sub> 2</sub>] and bis (5, 7-dimethyl-8-hydoxyquinolinato) zinc (II)[Zn (Me< sub> 2</sub> q)< sub> 2</sub>]. Zn (HPB)< sub> 2</sub> emitted light in blue region while Zn (Me< sub> 2</sub> q)< sub> 2</sub> emitted light in orange region of the visible spectrum.
Herein, we have synthesized a series of 2',6'-difluoro-2,3'-bipyridine cyclometalating ligands by... more Herein, we have synthesized a series of 2',6'-difluoro-2,3'-bipyridine cyclometalating ligands by
substituting electron-withdrawing (–CHO, –CF3, and –CN) and electron-donating (–OMe and –NMe2)
groups at the 4' position of the pyridyl moiety and utilized them for the construction of five new
iridium(III) complexes (Ir1–Ir5) in the presence of picolinate as an ancillary ligand. The photophysical
properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (–CN) group containing the iridium(III) compound (Ir3)
exhibits highly efficient genuine green phosphorescence (lmax = 508 nm) at room temperature
in solution and in thin film, with an excellent quantum efficiency (FPL) of 0.90 and 0.98, respectively.
On the other hand, the –CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission
(lmax = 468 nm) with a promising quantum efficiency (FPL = 0.88 and 0.84 in solution and in thin film,
respectively). The –CHO substituted iridium(III) complex (Ir1) showed greenish-yellow emission (lmax =
542 nm). Most importantly, the strong electron-donating –NMe2 substituted iridium(III) complex (Ir5)
gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (lmax =
520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum
efficiency, especially in thin-film noted in the case of the –OMe substituted iridium(III) complex (Ir4).
Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have
been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to
obtain information about the absorption and emission processes and to gain deeper insights into the
photophysical properties. The combinations of a smaller DES
1–T1 and higher contribution of 3MLCT in the
emission process result in the higher quantum yields and lifetime values for complexes Ir1–Ir3. Multilayered Phosphorescent Organic Light Emitting Diodes (PhOLEDs) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and their elecroluminescence properties were evaluated. Compound Ir4 at
a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7%, in the
nonoptimized device, and a power efficiency of 5.8 lm W1, together with a true-blue chromacity
CIE
x,y = 0.15, 0.17 recorded at the maximum brightness of 33 180 cd m2
We demonstrate a spatially uniform enhancement of individual quantum dot (QD) fluorescence emissi... more We demonstrate a spatially uniform enhancement of individual quantum dot (QD) fluorescence emission using plasmonic grating decouplers on thin gold or silver films. Individual QDs are deposited within the grating in a controlled way to investigate the position dependency on both the radiation pattern and emission enhancement. We also describe the optimization of the grating decoupler. We achieve a fluorescence enhancement ~3 times higher than using flat plasmon film, for any QD position in the grating.
We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fabricated u... more We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fabricated using a poly(methylmethacrylate) (PMMA) and lithium fluoride (LiF) composite dielectric. Increasing the concentration of LiF in the composite dielectric reduces the operating gate voltages significantly from 10 V to 1 V required leading to a decrease in resistance. Electron and hole mobility of 350 and 310 cm2/Vs at VD = -5 V are obtained for graphene FEDs with 10 % LiF concentration in the composite. Using composite dielectric also enabled excellent performance on flexible substrates without any significant change in mobility and resistance. Flexible FEDs with only 5 % and 12 % variation in mobility for 300 and 750 bending are obtained.
Energetic disorder in disordered organic solids has been found to alter their physical parameters... more Energetic disorder in disordered organic solids has been found to alter their physical parameters. Here, we have demonstrated, by means of Monte-Carlo simulation and experiments, that the electroluminescence (EL) spectrum is dependent on energetic disorder. This dependence has been attributed to the charge carrier relaxation during hopping process. The dependence of EL spectrum on energetic disorder makes it temperature dependent and temperature dependence has been found to vary with energetic disorder in a variety of materials. The simulation has been performed by taking the relaxation of charge carriers via transport energy in the Gaussian density of states. An analytical equation was established for spectral shift as a function of transport energy.
ABSTRACT Energetic disorder in disordered organic solids has been found to alter their physical p... more ABSTRACT Energetic disorder in disordered organic solids has been found to alter their physical parameters. Here, we have demonstrated, by means of Monte-Carlo simulation and experiments, that the electroluminescence (EL) spectrum is dependent on energetic disorder. This dependence has been attributed to the charge carrier relaxation during hopping process. The dependence of EL spectrum on energetic disorder makes it temperature dependent and temperature dependence has been found to vary with energetic disorder in a variety of materials. The simulation has been performed by taking the relaxation of charge carriers via transport energy in the Gaussian density of states. An analytical equation was established for spectral shift as a function of transport energy.
ABSTRACT We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fab... more ABSTRACT We demonstrate tunable solid state and flexible graphene field effect devices (FEDs) fabricated using a poly(methylmethacrylate) (PMMA) and lithium fluoride (LiF) composite dielectric. Increasing the concentration of LiF in the composite dielectric reduces the operating gate voltages significantly from 10 V to 1 V required leading to a decrease in resistance. Electron and hole mobility of 350 and 310 cm2/Vs at VD = -5 V are obtained for graphene FEDs with 10 % LiF concentration in the composite. Using composite dielectric also enabled excellent performance on flexible substrates without any significant change in mobility and resistance. Flexible FEDs with only 5 % and 12 % variation in mobility for 300 and 750 bending are obtained.
Electrical transport of pure and tetrafluoro-tetracyano-quinodimethane doped 4, 4′, 4 ″-tris (N-3... more Electrical transport of pure and tetrafluoro-tetracyano-quinodimethane doped 4, 4′, 4 ″-tris (N-3-methylphenyl-N-phenylamino) triphenylamine (m-MTDATA) films have been studied at various temperatures and doping concentrations. Pure films show space charge limited conduction with field and temperature dependent mobility. The J–V characteristics of doped m-MTDATA were ohmic at low voltages due to thermally released carriers from dopant states. At higher voltages the current density increases nonlinearly due to field dependent ...
We study the fluorescence emission from single dye molecules in coplanar plasmonic cavities compo... more We study the fluorescence emission from single dye molecules in coplanar plasmonic cavities composed of a thin gold film surrounded by two in-plane surface plasmon Bragg mirrors. We first discuss the effect of the presence of Bragg mirrors on the radiation diagram of surface plasmon coupled emission. Then, we investigate the role of the planar cavity size by single-molecule fluorescence lifetime imaging. Experimental data are compared to numerical simulations of the decay rates calculated as a function of the molecule orientation and position within the cavity. The creation of new decay channels by coupling to the cavity modes is also discussed. We measure a plasmonic Purcell factor up to five, attributed to the enhancement of the radiative rate.
In a search for blue light emitting multifunctional materials, the electron transport enhancing d... more In a search for blue light emitting multifunctional materials, the electron transport enhancing diphenyl phosphine–oxide (Ph2P[double bond, length as m-dash]O) group has been appended to blue light emitting pyrene derivatives. This design, we observe, leads to highly efficient electron transporting blue-emitters for non-doped organic light emitting devices (OLEDs) with good film formation characteristics. The superior performance is attributed to enhanced charge transport and formation of pyrene excimers assisted by thermally activated delayed fluorescence (TADF) in the device. We report the synthesis and characterization using experimental and computational methods of six such pyrene derivatives. Although three of these derivatives show quenching of luminescence in solvents at higher concentrations, in the thin film invariably all six of them exhibit typical pyrene excimer emission. X-ray crystal analysis reveals π–π stacking and the C–H[cdots, three dots, centered]O interactions in the solid due to the P[double bond, length as m-dash]O group. The measured electron mobilities for all the compounds are higher in comparison to the standard electron transport material, Alq3. Non-doped OLEDs with the pyrene derivatives as emitters (multi-layer configuration) as well as electron transport cum emitters (bilayer configuration) exhibit excellent efficiencies. The derivatives as emitters display a performance with current efficiencies (ηc) in the range 21.1–30.1 cd A−1, power efficiencies (ηp) 11.0–15.76 lm W−1, external quantum efficiencies (EQE) 7.2–9.1% and brightness 28[thin space (1/6-em)]500–42[thin space (1/6-em)]750 cd m−2. In addition, the derivatives as electron transporting emitters demonstrate very good external quantum efficiencies in the range of 3.0–4.0%. These results demonstrate a successful strategy to obtain blue light emitting multifunctional materials for OLED applications.
In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2-phenyl-1... more In this work, we present a detailed analysis on electron transport studies of 9,10-bis(2-phenyl-1,3,4-oxadiazole) derivatives of anthracene (OXD-PH, OXD-PTOL and OXD-OTOL). The effect of methyl substitution at ortho (OXD-OTOL) and para position (OXD-PTOL) on the phenyl ring on the electron transport properties was studied and the results were compared with the anthracene derivative without any substitution at the phenyl ring. Electron transport was found to be highly dependent on the methyl substitution and electron mobilities in OXD-PTOL and OXD-OTOL were found to be lower than in OXD-PH. Mobilities were also found to be different for OXD-PTOL and OXD-OTOL, which indicates that the substitution at different places did not have a similar effect on charge transport properties. Thickness dependent trap states were observed for all three molecules with thickness dependent electron mobilities. Electron mobility was found to increase in all three molecules with the decrease in thickness, which favors their use for organic electronic devices and all three molecules had a better electron transport in comparison to Alq3. These results were explained by the DFT calculation which showed a dihedral structure. The dihedral angle was found to reduce in the anionic form of these molecules. Therefore, these molecules are likely to favor a proper stacking in the solid state form.
Color stability in multi-emissive layer organic light emitting devices (Me-OLEDs) has been invest... more Color stability in multi-emissive layer organic light emitting devices (Me-OLEDs) has been investigated. Me-OLEDs were based on multiple emitters with a common host CBP doped with three dopants, BCzVBi, Ir (ppy) 3 and Ir (btp) 2acac for blue, green and red emission. A major variation in CIE coordinates were found from (0.312, 0.294) to (0.236, 0.267) with increase in voltage from 6 to 9V. This coordinate shift in Me-OLEDs has been attributed to the shifting of recombination zone with increase in voltage.
Abstract Nanostructures of indium tin oxide (NSITO) deposited using glancing angle deposition (GL... more Abstract Nanostructures of indium tin oxide (NSITO) deposited using glancing angle deposition (GLAD) technique are used to enhance the outcoupling efficiency of blue and green OLEDs. The enhancement was found to be angle independent. The efficiency of device has increased by about 2.1 times by the use of NSITO at glass/air interface and ITO/glass interface. Similarly nano-phosphor particles were used to recover the glass modes by depositing them on the backside of the substrates.
abstract White organic light emitting diodes were fabricated using two zinc complexes bis (2-(2-h... more abstract White organic light emitting diodes were fabricated using two zinc complexes bis (2-(2-hydroxyphenyl) benzoxazolato) zinc (II)[Zn (HPB)< sub> 2</sub>] and bis (5, 7-dimethyl-8-hydoxyquinolinato) zinc (II)[Zn (Me< sub> 2</sub> q)< sub> 2</sub>]. Zn (HPB)< sub> 2</sub> emitted light in blue region while Zn (Me< sub> 2</sub> q)< sub> 2</sub> emitted light in orange region of the visible spectrum.
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Papers by Arunandan Kumar
substituting electron-withdrawing (–CHO, –CF3, and –CN) and electron-donating (–OMe and –NMe2)
groups at the 4' position of the pyridyl moiety and utilized them for the construction of five new
iridium(III) complexes (Ir1–Ir5) in the presence of picolinate as an ancillary ligand. The photophysical
properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (–CN) group containing the iridium(III) compound (Ir3)
exhibits highly efficient genuine green phosphorescence (lmax = 508 nm) at room temperature
in solution and in thin film, with an excellent quantum efficiency (FPL) of 0.90 and 0.98, respectively.
On the other hand, the –CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission
(lmax = 468 nm) with a promising quantum efficiency (FPL = 0.88 and 0.84 in solution and in thin film,
respectively). The –CHO substituted iridium(III) complex (Ir1) showed greenish-yellow emission (lmax =
542 nm). Most importantly, the strong electron-donating –NMe2 substituted iridium(III) complex (Ir5)
gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (lmax =
520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum
efficiency, especially in thin-film noted in the case of the –OMe substituted iridium(III) complex (Ir4).
Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have
been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to
obtain information about the absorption and emission processes and to gain deeper insights into the
photophysical properties. The combinations of a smaller DES
1–T1 and higher contribution of 3MLCT in the
emission process result in the higher quantum yields and lifetime values for complexes Ir1–Ir3. Multilayered Phosphorescent Organic Light Emitting Diodes (PhOLEDs) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and their elecroluminescence properties were evaluated. Compound Ir4 at
a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7%, in the
nonoptimized device, and a power efficiency of 5.8 lm W1, together with a true-blue chromacity
CIE
x,y = 0.15, 0.17 recorded at the maximum brightness of 33 180 cd m2
substituting electron-withdrawing (–CHO, –CF3, and –CN) and electron-donating (–OMe and –NMe2)
groups at the 4' position of the pyridyl moiety and utilized them for the construction of five new
iridium(III) complexes (Ir1–Ir5) in the presence of picolinate as an ancillary ligand. The photophysical
properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (–CN) group containing the iridium(III) compound (Ir3)
exhibits highly efficient genuine green phosphorescence (lmax = 508 nm) at room temperature
in solution and in thin film, with an excellent quantum efficiency (FPL) of 0.90 and 0.98, respectively.
On the other hand, the –CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission
(lmax = 468 nm) with a promising quantum efficiency (FPL = 0.88 and 0.84 in solution and in thin film,
respectively). The –CHO substituted iridium(III) complex (Ir1) showed greenish-yellow emission (lmax =
542 nm). Most importantly, the strong electron-donating –NMe2 substituted iridium(III) complex (Ir5)
gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (lmax =
520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum
efficiency, especially in thin-film noted in the case of the –OMe substituted iridium(III) complex (Ir4).
Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have
been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to
obtain information about the absorption and emission processes and to gain deeper insights into the
photophysical properties. The combinations of a smaller DES
1–T1 and higher contribution of 3MLCT in the
emission process result in the higher quantum yields and lifetime values for complexes Ir1–Ir3. Multilayered Phosphorescent Organic Light Emitting Diodes (PhOLEDs) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and their elecroluminescence properties were evaluated. Compound Ir4 at
a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7%, in the
nonoptimized device, and a power efficiency of 5.8 lm W1, together with a true-blue chromacity
CIE
x,y = 0.15, 0.17 recorded at the maximum brightness of 33 180 cd m2