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Novel thermally-activated delayed fluorescence (TADF) host materials were designed for blue electrophosphorescence by combining electron donor acridine derivatives with the electron acceptor phenox...

Novel thermally activated delayed fluorescence (TADF) emitters were designed with diphenylsulfone (DPS) as an electron acceptor and carbazole derivatives as electron donors and their electr...

Novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence were developed by combining the electron donor acridine derivatives with the electron ac...

Novel thermally activated delayed fluorescence (TADF) materials with 6-position modified benzofuro[2,3-b]pyridine (6BFP) as an electron acceptor and phenylcarbazole derivatives [9-phenyl-1,...

An asymmetric A-π-D-π-A’ organic dye (dye1) combining a red D − π−A dye (D35) and a blue D − π−A’ dye (DB) on each side of a triphenylamine (TPA) was designed, and a theoretical study was c...

Novel thermally activated delayed fluorescence (TADF) emitters with carbazole (Cz) as an electron donor and thianthrene 5,5-dioxide (TTDO) and 9,9-dimethyl-9H-thioxanthene 10,10-dioxide (DMTA) as a...

Novel thermally activated delayed fluorescence (TADF) materials (PCD-TRZ and PCCD-TRZ) with 9,9-dimethyl-9,10-dihydroacridine derivatives (PCD and PCCD) as electron donors and a triphenyl-triazine ...

We investigated the effect of heteroleptic dual electron acceptor as a photosensitizer for the dye-sensitized solar cells (DSSCs). Novel tribranched organic dyes were designed with heteroleptic dua...

In this study, novel porphyrin-based dye sensitizer with diphenylamine (DPA) as the electron donating group, isoindigo (II) as the electron withdrawing group, and carboxylic acid (CA) with benzene as the anchoring part (YD2-II-CA) were theoretically investigated in comparison with the recent best dye (YD2-o-C8). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to gain insight into the factors responsible for photovoltaic performance. Due to the substitution of the electron withdrawing unit, the absorption spectra of YD2-II-CA was more red-shifted and broader than the spectrum of the YD2-o-C8. The results suggest that this novel porphyrin-based dye would have good photovoltaic properties in dye-sensitized solar cells (DSSCs)

A novel 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino) styryl]-4H-pyran (DCM)-based organic dye with a heteroleptic dual-electron donor was designed, and its electronic and optical properties were investigated theoretically for dye-sensitized solar cells (DSSCs). We designed three dyes with triphenylamine (T) and phenoxazine (P) moieties on each side of a DCM-based organic dye (D); namely, TPDPT, TPDTP, and PTDTP. In this study, heteroleptic TPDTP dye was compared with the homoleptic dyes (TPDPT and PTDTP). The absorption spectrum of the dyes showed different forms because of the different energy levels of the molecular orbital (MO) of each dye and intramolecular energy transfer. It was shown that the energy antenna group created an additional absorption band around 430 nm and caused a cascading two-electron process aiding the charge-separation process. Absorption Band 1 (around 640 nm) and Band 2 (around 520 nm) showed that P→D and T→D, respectively. It was expected that the TPDTD dye with th...

We have designed novel thermally activated delayed fluorescence (TADF) materials, 2DMACPN and 2DMACTPN, with 9,9-dimethyl-9,10-dihydroacridine (DMAC) as an electron donor and dicyanobenzene as an electron acceptor. We obtain the zero-zero transition energies of the first excited singlet (S1) and first triplet excited (T1) states of TADF materials by performing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations on the ground state using a dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. The calculated ΔEST values of 2DMACPN (0.019 eV) and 2DMACTPN (0.023 eV) were smaller than those of 2CzPN (0.363eV) and 2CzTPN (0.178eV) because of the large dihedral angles between the plane of DMAC and the connected phenyl rings of PN and TPN. We show that 2DMACPN would have the highest TADF efficiency among the four compounds because it has the largest dihedral angle, which creates a small spatial overlap b...

In this study, three triphenylamine (TPA)-based dye sensitizers with phenothiazine (PTZ) and TPA as dual-electron donors, benzothiadiazole (BTD) as an electron withdrawing unit, and cyanoacetic acid as an electron acceptor (dye1, dye2, dye3, dye4) were designed and investigated. To decrease the energy band gap of dye1, we added π-conjugation between the PTZ donor and the TPA donor in dye1 and/or BTD between the TPA and thiophen in dye1. Using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, we gained insight into the factors responsible for photovoltaic performance. Due to the different energy band gaps of each dye, the absorption spectra of the dyes each showed a different form. Among the dyes, dye4 showed the most red-shifted and broadest absorption spectra. It is expected that dye4 would have better photovoltaic properties than the others. This work indicates that adding π-conjugation or a withdrawing unit into dye would result in good photovoltaic properties for dye-sensit...

Novel heteroleptic ruthenium(II) complex was designed and investigated theoretically, [Ru(F2HexOppy)(NCS)(tctpy)] with ppy derivative for heteroleptic donor to increase molar absorptivity compared to N749 (tctpy = 4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine, F2HexOppy = 2-(2’,4’-difluorophenyl)-4-oxyhexylpyridine). Generally, absorption spectrum of dyes with ppy derivative was red-shifted and broadened compared to N749, especially, in the region above 650nm. This is attributed to the heteroleptic donor system of these dyes. According to the molecular orbital analysis, we observed the LUMO mainly localized on tctpy (4,4′,4″-tricarboxy-2-2′:6′.2″-terpyridine) moiety in N749. In case of HOMOs were localized on NCS moiety. However, HOMO of [Ru(F2HexOppy)(NCS)(tctpy)] were delocalized over Ru-F2HexOppy-NCS and HOMO-1 were delocalized on Ru-NCS moiety, respectively. These results, new type Ru(II) complex would show higher photovoltaic efficiency compared to N749 as dye sensitizers.

New triphenylamine and indoline-based dyes with dual donor and dual acceptor were designed and their electronic and optical properties were investigated by using density functional theory and time-dependent density functional theory calculations. The results showed that the homoleptic and heteroleptic dual acceptors of the dyes (C-TPA-In-C, R-TPA-In-C) intensified each absorption band between 450 and 600 nm, compared to the single acceptor of the reference dye (TPA-In-C). Considering overall properties, it is expected that the R-TPA-In-C dye with dual electron acceptor would show highest performance of the dyes in conversion efficiency for dye-sensitized solar cells.

In this work, we designed and investigated theoretically novel ruthenium(II) complex (Bu4N)[Ru(DMFAdctpy)(NCS)3]; (DMFAdctpy : 2-(6-(5-(4-(bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)pyridin-2-yl)-4-carboxypyridin-2-yl)pyridine-4-carboxylic acid) with DMFAdctpy as an anchoring group and a highly conjugated ancillary ligand to increase absorption ability in the long wavelength region compared to the N3 dye([Ru(dcbpy)2(NCS)2]); (dcbpy (4,4′-dicarboxy-2,2′-bipyridine)). The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to gain insight into the factors responsible for photovoltaic properties as dye sensitizer. The absorption spectrum of these dyes with terpyridine derivative is more red-shifted and broad than that of N3, especially, in the region between 400 nm and 650 nm. This is attributed to the extension of the π-conjugated system of insertion terpyridine ligands. Molecular orbital analysis confirmed that the HOMOs of (Bu4N)[Ru(DMFAdctpy)(NC...

In this study, heteroleptic ruthenium complex Ru(dcbpy)(quqo)(NCS)2 (dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) where the quqo was 2-(2-quniolinyl)quinoxaline, was designed and studied theoretically. To gain insight into their structural, electronic and optical properties using DFT calculations were performed on Ru(dcbpy)(quqo)(NCS)2 derived from the N3 dye. Molecular orbitals analysis confirmed that HOMOs of Ru(dcbpy)(quqo)(NCS)2 are localized over the NCS ligand orbitals and the LUMO is localized over the quqo moiety. For N3, HOMOs are localized over the NCS moiety, however LUMO is localized over the dcbpy moiety. The TDDFT calculations showed that the new heteroleptic complex had more panchromatic absorption spectra in the region above 600 nm compared to N3 dye. Absorption bands around 600 nm are due to the conjugated length of quqo ligand.

Herein, as a photosensitizer for the dye-sensitized solar cells (DSSCs), we designed a novel organic dye with heteroleptic dual electron acceptors (rhodanine-3-acetic acid and cyanoacrylic acid) on each side of a triphenylamine-based organic dye. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to estimate the photovoltaic properties of the dyes. It was found that the dyes with dual acceptor groups (DB-2, DB-3) showed stronger and more red-shifted intensities from the absorption spectra. Due to the proximity of the lowest unoccupied molecular orbitals (LUMO) to the anchoring carboxylic group, it was also shown that DB-3 with cyanoacrylic acid and rhodanine-3-acetic acid acceptors might be more effective in Jsc than DB-2 with rhodanine-3-acetic acid acceptors. From these results, it is suggested that the DB-3 dye with heteroleptic dual acceptors would show better photovoltaic performance than other dyes in this study as a dye sensitizer for DSSCs.

In this study, we have compared the well known N3 dye and Ru(II) complex substituted with antenna group, such as two pyrenes of both site to bipyridine. Molecular orbital analysis confirmed that the LUMO and LUMO+1 are essentially delocalized over the dcbpy and the antenna ligand, respectively. The TD-DFT calculations showed that the complex with pyrene antenna had more panchromatic absorption spectra in the region above 400 nm compared to N3 dye. Moreover, the absorption bands around between 400 and 550 nm were red-shifted and increase molar extinction coefficients due to the antenna unit.

Herein, indoline-based dye sensitizers with dual and triple electron donors (the TPA-In and the POZ-TPA-In dye) were designed and their electronic and optical properties were investigated theoretically to enhance photovoltaic performance as dye-sensitized solar cells (DSSCs). To gain insight into the factors responsible for photovoltaic efficiencies, we perform the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations for these dyes. This study shows that all electron donor moieties might contribute to absorption process even for the dye with triple electron donor. From DFT and TDDFT calculations as well as frontier orbital analysis, this result is attainable when HOMO levels of the POZ-TPA-In dye were manipulated appropriately. It suggests that dye sensitizer with multiple electron donor could show better photovoltaic properties in case of proper design of its MO levels and consequently increase the conversion efficiency for DSSCs.

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dppzc)(PPhMe2)2(H)(L) (L = Cl, CN) [dppzc = 1,3-Diphenyl-1H-pyrazole-4-carboxaldehyde] were studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. We investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the complexes. From these results, we discussed how the ancillary ligand influences the emission peak as well as the metal to ligand charge transfer (MLCT) transition efficiency. The calculated energies of triplets are 3.09 and 3.16 eV, respectively, which are all higher than that of Ir(dfppy)2(acac) and FIrpic known as blue phosphorescence materials with 2.69 and 2.73 eV.

Highly effective phenoxazine (POZ)–based dyes (dye1, dye2, dye3, dye4 and dye5) for dye-sensitized solar cells (DSSCs) were designed and studied theoretically by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. When the electronic properties of dye2 were further analyzed in terms of the coupling among its moieties, it was found that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the dye2 was originated from the HOMO of the POZ and the triphenylamine moieties and the LUMO of the cyanoacrylic acid moiety, respectively. It was found that HOMO = >LUMO (and HOMO-1 = >LUMO) transition could be considered as an intramolecular charge-transfer (ICT) transition and HOMO = >LUMO+1 transition, however, as the mixture of ICT and π–π* excitation. It was shown that through the additional electron donating group, absorption bands due to HOMO = >LUMO transition were red-shifted and another strong absorption bands a...

The synthesis and photophysical study of efficient phosphorescent iridium(III) complexes having two different (C^N) ligands are reported. In order to improve luminescence efficiency by avoiding triplet–triplet (T-T) annihilation, a heteroleptic iridium complex, Ir(dpq)2(piq), is designed and prepared, where dpq and piq represent 2,4-diphenylquinoline and 1-phenylquinoline, respectively. Dpq and piq ligands can act as a source of energy. When Ir(dpq)2(piq) is placed in the lowest excited state, the excitation energy is neither quenched nor deactivated but quickly transferred intermolecularly from two dpq ligands to one luminescent piq ligand. Such transfer can occur because the triplet energy level of dpq is higher than that of piq and light is emitted mainly from the piq ligand in the end. Thus, Ir(dpq)2(piq) shows strong photoluminescence from piq ligands. To analyze this luminescent mechanism, we calculated these complexes theoretically using a computational method.

In this study, the heteroleptic tris-cyclometalated iridium complex, bis(2-phenylquinoline)(2-phenylpyridine)iridium(III) [Ir(pq)2(ppy)], used as red emitting dopant for white organic light-emitting diodes (WOLEDs) had higher maximum luminescence efficiency (13.80 cd/A) than that of the homoleptic tris-cyclometalated iridium complex, tris(2-phenylquinoline)iridium(III) [Ir(pq)3], due to the presence of a sensitizing ppy ligand. Thus, WOLEDs combining the Ir(pq)2(ppy) as a red emissive phosphorescent material and 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) as a blue emissive fluorescent material have been studied. The WOLEDs were optimized by adjusting the device structure, the optimized WOLED (device 10) had a maximum luminescence efficiency of 16.90 cd/A and CIE coordinates of (0.407, 0.337) at the applied voltage of 12 V.

A novel red phosphorescent heteroleptic tris-cyclometalated iridium complex, Ir(ppy)2(dpq) based on 2-phenylpyridine (ppy) and 2,4-diphenylquinoline (dpq) ligand was synthesized and characterized for application in organic light-emitting diodes (OLEDs). The heteroleptic tris-cyclometalated iridium complex leads to a significant improvement in luminescence efficiency by cascade exciton transfer and the avoidance of triplet-triplet (T-T) annihilation. A ppy ligand with triplet state energies intermediate between that of the host and the emitting ligand can be successfully employed as “sensitizing ligand” allowing for efficient energy transfer from the host to the emitting ligand. A maximum luminance efficiency of ηc = 14.06 cd/A was achieved at a current density of J = 20.94 mA/cm2. At a higher current density of J = 100 mA/cm2, an efficiency of ηc = 10.77 cd/A was obtained.

Novel red-emitting electrophosphorescent devices were fabricated by doping an Ir complex, Ir(tpq)2(acac), based on 2,3,4-triphenylquinoline (tpq) ligand. The EL spectrum of the device showed emission maximum peak at 611 nm and CIE coordinates of that were (0.664, 0.332) at 12 V, respectively, due to long conjugation length of Ir(tpq)2(acac). The luminance of the device with Ir(tpq)2(acac) was 4160 cd/m2 at 14 V. The maximum luminous efficiencies and power efficiency of the device with Ir(tpq)2(acac) were 3.14 cd/A (8.01 mA/cm2) and 1.82 lm/W (0.24 mA/cm2). More characteristics and charge transport mechanism will be discussed.

In this study, a new Ir(III) complex containing 2-(3′,5′-bistrifluoromethyl phenyl)-4-methoxypyridine have been synthesized and characterized for efficient blue organic light-emitting diodes (OLEDs). In order to tune photoluminescence (PL) spectra to a shorter wavelength, ppy ligand was fluorinated by –;CF3 and substituted by –OCH3 group. The methoxy group substituted on the 4-position of pyridyl ring as electron donating group strongly affected the lowest unoccupied molecular orbital (LUMO) and it raised the LUMO energy and increased the energy gap. The trifluoromethyl group substituted on the 3′,5′-position of phenyl ring as electron withdrawing group decreased the highest occupied molecular orbital (HOMO), and bulky CF3 groups occurs a steric hindrance of iridium complex helps decrease of self-quenching. As a result, Ir[(CF3)2OMeppy]2(acac) is more blue-shifted emission at 471 nm and strong luminescence efficiency.

Novel red electrophosphorescent devices were fabricated by doping perfluorophenyl substituted iridium(III) complex, bis[1-(6-Pentafluorophenyl-2,4-diphenyl)quinolinato-N,C2′] iridium(III) (acetylacetonate) [Ir(PF-dpq)2(acac)] for the application in organic light-emitting diodes (OLEDs). The maximum electroluminescent (EL) wavelengths of Ir(dpq)2(acac) and Ir(PF-dpq)2(acac) have shown at 614 nm and 620 nm, respectively. The device using Ir(PF-dpq)2(acac) showed red emission with 1931 CIE chromaticity coordinates (x = 0.640, y = 0.342) at 12 V. The perfluorophenyl substituent on the quinoline ring as electron withdrawing group decreased the lowest unoccupied molecular orbital (LOMO). As a result, the energy gap is reduced, leading to red-shift the emission wavelength. The ab initio calculation using the time-dependent density function theory (DFT) showed in agreement with the experimental results. However, the iridium complex of PF-dpq underwent a weak MLCT transition because of the weak coupling between th...

Novel red phosphorescent heteroleptic tris-cyclometalated iridium complex, Ir(ppy)2(dpq-3F) based on 2-phenylpyridine (ppy) and 2-(3-fluorophenyl)-4-phenylquinoline (dpq-3F) ligands have been synthesized and characterized for the application in organic light-emitting diodes (OLEDs). The heteroleptic tris-cyclometalated iridium complex leads to a significant improvement in a luminous efficiency at high currents to avoid the T–T annihilation by the exciton transfer from two ppy ligands to one luminescent dpq-3F ligand decreasing the number of the luminescent ligand. This inter-ligand energy transfer (ILET) can occur because the dpq-3F-centered 3MLCT state is lower than that of the ppy-centered 3MLCT state and because the ILET time from the ppy-centered 3MLCT state to the dpq-3F-centered 3MLCT state is shorter than the radiative lifetime of Ir(ppy)3. A maximum luminous efficiency of ηc = 13.70 cd/A and power efficiency of ηp = 10.80 lm/W are achieved at a current density of J = 0.07 mA/cm2. At a higher curre...

The synthesis and photophysical study of efficient phosphorescent iridium(III) complex having two different (C∧N) ligands are reported. In order to improve the luminescence efficiency by avoiding triplet–triplet (T–T) annihilation and study luminescent mechanism of the heteroleptic iridium complex, Ir(piq-3F)2 (dpq-4F) is designed and prepared where piq-3F and dpq-4F represent 1-(4′-fluorophenyl)isoquinoline and 2-(3′-fluorophenyl)-4-phenylquinoline, respectively. We thought that both piq-3F and dpq-4F ligands can act as a source of energy supply because of the relative HOMO energy level and the luminescence lifetime of homoleptic Ir complexes Ir(piq-3F)3 Ir(dpq-4F)3. However the UV-vis absorption spectra and the PL spectra of Ir(piq-3F)2 (dpq-4F) is more similar to that of Ir(piq-3F)3. In spite of lower triplet energy level of dpq-4F, the excitation energy is not intramolecular transferred from two piq-3F ligands to one dpq-4F ligand. The luminescence occurs mainly at piq-3F ligand. It is due to the stro...

The synthesis and photophysical study of efficient phosphorescent iridium(III) complexes having two different (C ˆ N) ligands are reported. In order to improve the luminescence efficiency by avoiding triplet-triplet (T-T) annihilation, the iridium complexes, Ir(ppy)2(dpq) and Ir(ppy)2(dpq-3-F), are designed and prepared where ppy, dpq and dpq-3-F represent 2-phenylpyridine, 2,4-diphenylquinoline and 2-(3-fluorophenyl)-4-phenylquinoline, respectively. Since Ir(ppy)3, Ir(dpq)3 and Ir(dpq-3-F)3 can be placed in the metal-to-ligand charge transfer (MLCT) excited state, they absorb light effectively. Thus, ppy ligands and a dpq derivative can act as a source of energy supply. When Ir(ppy)2(dpq-3-F) is placed in the lowest excited state, the excitation energy is not quenched nor deactivated but quickly transferred intramolecularly from two ppy ligands to one luminescent dpq-3-F ligand. Such transfer can occur because the triplet energy level of ppy is higher than that of dpq-3-F and light is emitted from dpq-3-...

In order to tune the emission to be pure red and increase the efficiency, new iridium complex, Ir(PF-piq)2(acac), is designed and studied, where piq, PF-piq and acac represent phenylisoquinoline, 4-(perfluorophenyl)-1-phenylisoquinoline and acetylacetonate, respectively. The Hartree-Fock (HF) method with the 3-21G(d) basis set and density functional theory (DFT) utilizing the B3LYP functional with the 6-31G(d) basis set were used for the geometry optimization and the energy level calculation of the ground state of this complex, respectively. The excited triplet and singlet states are examined using the time-dependent density functional theory (TD-DFT). As a result, it is confirmed theoretically that the wavelength of new iridium complex were shifted toward the red region when introducing a pentafluorophenyl group. The efficiency and brightness of the complex are predicted to increase in comparison with those of Ir(piq)2acac.

Previously, we studied the luminescence characteristics of Ir(ppy)2(F2-ppy) and Ir(ppy)2(piq-F), which are heteroleptic iridium complexes involving two kinds of ligands, where F2-ppy, ppy and piq-F represent 2-(2,4-difluoro-phenyl)-pyridine, 2-phenylpyridine and 1-(4′-fluoroyphenyl)isoquinoline, respectively. Photoluminescence (PL) spectrum of Ir(ppy)2(F2-ppy) showed an emission peak at 495 nm in bluish green area. Ir(ppy)2(piq-F) showed two peaks at 513 nm and 600 nm in the PL spectrum. In order to make a white phosphorescent emitter for OLED, we herein designed a heteroleptic iridium complex containing three different ligands. We thought that reaction of F2-ppy, ppy and piq-F ligands all together with Ir(acac)3 might lead to Ir(F2-ppy)(ppy)(piq-F) among the mixture, displaying red and bluish green emission simultaneously. Ir(F2-ppy)(ppy)(piq-F) and other double-heteroleptic complex mixture are prepared from various concentration combination of ligands. The heteroleptic iridium complex mixture displays a...

We propose novel optical configurations of liquid crystal cells in double cell gap structure for transflective displays. The transmissive part as well as the reflective part is designed in the wide-band quarter-wave structure to achieve the good dark state. We found that in-plane switching of the proposed structure can provide a perfect bright state, although not only in-plane switching but also vertical switching can be used to achieve the bright state. It is also expected that wide viewing angle can be achieved at the same time by employing the in-plane switching mode.

Luminescence efficiency of pyrene molecule is very low because of the aggregation effect of planar pyrene molecules. However, 1,3,6,8-tetra-substituted pyrenes with large electron donating group were reported to give a bright blue fluorescence [1]. In this paper, 1,6-bi-substituted and 1,4,6,9-tetra-substituted pyrenes as well as 1,3,6,8-tetra-substituted pyrenes were studied to find out the possibilities as the blue fluorescent materials of organic light-emitting diodes (OLEDs) [2-4]. Geometrical and electrical calculations were performed by ab initio methods. HF/3-21G(d) basis set was used for the geometry optimization of the ground electronic states of those compounds. The geometry of the low-lying excited electronic state was optimized using configuration interaction with single excitation (CIS) method. The vertical and adiabatic transition energies were calculated by time-dependent density functional theory (TD-DFT) using the B1LYP functional with 6-31G(d) basis set. From calculational results, it wa...

There have been reported materials emitting green color in both fluorescence and phosphorescence with great success, however efficient red luminescence materials are rare. Recently, it has been reported iridium (III) complexes of 1-(phenyl)isoquinoline ( piq ) and 1-(4′-fluorophenyl) isoquinoline ( piq-F ) show strong electroluminescence (EL) brightness and efficiency, even at high currents. These complexes show the strong intensity of band around 450 nm assigned to the spin-forbidden 3MLCT (metal to ligand charge transfer) transition [1]. In this study, Ir(III) complexes of fluorinated piqs ( piq-F , piq-2F , piq-CF 3 ) as cyclometalated ligand were prepared and photonic properties were investigated to improve the EL efficiency. The Ir(III) complex with piq-CF 3 ligands exhibits the largest emission efficiency with maximum at 612 nm. The result of ab. Initio calculation using the Time-dependent density functional theory (TD-DFT) shows that the strong 3MLCT transition of the complex is due to the strong c...

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dFOMeppy)(PPh3)2(H)(Cl), [Ir(dFOMeppy)(PPh3)2(H)(NCMe)]+ and Ir(dFOMeppy)(PPh3)2(H)(CN), [dFOMeppy = 2-(2′,4′-difluorophenyl)-4-methoxypyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To achieve deep blue emission, the difluoro group substituted on the phenyl ring and the methoxy group substituted on the pyridyl ring increased HOMO-LUMO gap and achieved the hypsochromic shift. To gain insight into the factors responsible for the emission color change and the different luminescence efficiency, we investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the complexes. From these results, we discuss how the ancillary ligand influences the emission peak as well as the metal to ligand charge trans...

In this study, new deep blue emitting mixed ligand iridium(III) complexes such as Ir(dFppy)(PPhMe2)2(H)(Cl), [Ir(dFppy)(PPhMe2)2(H)(NCMe)]+ and Ir(dFppy)(PPhMe2)2(H)(CN), [dFppy = 2-(2′,4′-difluoro-phenyl)pyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. These iridium complexes comprise one cyclometalating, two phosphines trans to each other and two cis-ancillary ligands. We investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the three complexes to gain insight into the factors responsible for the emission color change and the different luminescence efficiency. Reducing the molecular weight of phosphine ligand with PPhMe2 leads to a strategy of the efficient deep blue organic light-emitting devices (OLED) by thermal processing instead of the solution processing. The electron-withdrawing difluoro group substituted on t...

We report the theoretical studies of cationic Ir(III) complexes with phenylpyridine and phosphines, [trans-Ir(dfMeppy)2(PPh2Me)2]+ and [cis-Ir(dfMeppy)2(PPh2Me)2]+. To gain insight into the factors responsible for the emission color change and the different quantum yields, we perform DFT and TDDFT calculations on the ground and excited states of these complexes, including solvation effects on the calculation of the excited states. [Trans-Ir(dfMeppy)2(PPh2Me)2]+ produces the PL emission at 450 and 475 nm, whereas [cis-Ir(dfMeppy)2(PPh2Me)2]+ produces the PL emission at 442 and 470 nm, respectively. The computational study allows us to reveal that the position of the PPh2Me ancillary ligands alter the MLCT energy mainly by changing the HOMO energy level. The HOMO energy level of the cis-isomer may be lowered by a high trans effect of the strong-field ancillary ligand, which causes a significant blue shifted emission. It is also likely that the strong-field ancillary ligand PPh2Me increases the MLCT characte...

White organic light-emitting devices (WOLEDs) consist of a fluorescent blue material doped in a region spatially separate from the phosphorescent dopant iridium complex. This study evaluated two potential new phosphorescent materials, the heteroleptic tris-cyclometallated iridium complexes Ir(tpy)2(btp) and Ir(btp)2(tpy), where tpy and btp are “2-(p-tolyl)pyridine” and “2-(2′-benzothienyl)pyridine”, respectively. The luminescence mechanism in heteroleptic iridium complexes is determined by the rates of decay from two different species of ligands. The quantum yields (lifetime) of fac-Ir(tpy)3 and fac-Ir(btp)3 were reported as 0.5 (2.0 μs) and 0.12 (4.0 μs), respectively. Thus, the radiative decay rate (k r ) of fac-Ir(tpy)3 and fac-Ir(btp)3 can be calculated as 2.5 × 105/s and 3.0 × 104/s, respectively. Heteroleptic tris-cyclometallated iridium complexes were able to tune the color for white phosphorescent materials, by controlling the radiative decay rate of ligands and number of ligands in complexes.

To examine the substituent effect, 5′-substituted 2,4-diphenylquinoline (dpq) ligands and their iridium complexes, Ir(dpq)2(acac), Ir(dpq-5F)2(acac), Ir(dpq-5CH3)2(acac) and Ir(dpq-5OCH3)2(acac), were synthesized and prepared, and the photophysical properties were investigated for red electro-phosphorescent materials. The 5′-substituted phenyl ring generated 3′-positon and 5′-position isomers. However, the 5′-position of the phenyl ring is more stable than the 3′-position due to steric effects. The maximum emission wavelengths of Ir(dpq)2(acac), Ir(dpq-5 F)2(acac), Ir(dpq-5CH3)2(acac) and Ir(dpq-5OCH3)2(acac) were found at 612, 606, 616, 606 nm, respectively. The emission spectrum of Ir(dpq-5CH3)2(acac) was red shifted compared to that of Ir(dpq)2(acac) because the methyl group substituted on the 5′-position of the phenyl ring is an electron donating group. Ir(dpq-5 F)2(acac) shows highly efficient and blue-shifted luminescence because the electron withdrawing group (-F) substitute on the 5′-position of t...

In this study, new deep blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other and two cis-ancillary ligands, such as Ir{(CF3)2Meppy}(PPh3)2(H)(Cl), [Ir{(CF3)2Meppy}(PPh3)2(H)(NCMe)]+ and Ir{(CF3)2Meppy} (PPh3)2(H)(CN), [(CF3)2Meppy = 2-(3′,5′-bis-trifluoromethylphenyl)-4-methylpyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. We investigate the strong field capabilities of ancillary ligands to gain insight into the factors responsible for the emission color change and the different luminescence efficiencies. This work represents a strategy for the design of deep blue phosphorescent iridium complexes. The electron-withdrawing trifluoromethyl group substituted on the phenyl ring, the electron-donating methyl group on the pyridyl ring and the cyano strong field ancillary ligand increase HOMO-LUMO gap to achieve the hypsochromic shift in emission colo...

In this study, a series of new blue phosphorescent iridium(III) complexes with ligands of (CF3)2Meppy [(CF3)2Meppy = 2-(3′,5′-bis-trifluoromethylphenyl)-4-methylpyridine] were successfully synthesized and their photophysical properties were systematically investigated. To analyze color tuning effected by changing the ancillary ligands, we have measured UV-absorption and photoluminescence (PL) spectra and have theoretically calculated the iridium complexes with different ancillary ligands using computational methods. The maximum emission spectrum of Ir[(CF3)2Meppy]2(acac), Ir[(CF3)2Meppy]2(pic), Ir[(CF3)2Meppy]2(taz) and Ir[(CF3)2Meppy]2(N4) were 473.5, 472, 475 and 468 nm, respectively. However, the PL efficiency was not improved by changing the picolinate ligands with other ancillary ligands, such as triazolate or tetrazolate ions. We discuss how the ancillary ligand influences both the emission peak and the metal to ligand charge transfer (MLCT) transition efficiency.