Lowest-lying Absorptions Research Articles

A series of theoretical studies on phosphorescent materials based on deep red/near-infrared iridium complex with low-efficiency roll-off performance

Organic light-emitting diodes (OLEDs) have been widely used in various fields such as sensors. In this article, we designed six novel heterocyclic Ir(III) complexes: (CFM)2Ir(acac) (named 1 in this paper), (TTIQ)2Ir(acac) (named 2), (CFM)2Ir(tmd) (named 3), (TTIQ)2Ir(tmd) (named 4), (CFM)2Ir(pic) (named 5) and (TTIQ)2Ir(pic) (named 6). The six iridium (III) complexes were calculated using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT). We studied the bands of the lowest-lying absorptions and lowest energy emissions of complexes 1–6. In addition, we also explored their spectral properties, frontier Molecular Orbital theory(FMO) and spin-orbital coupling value(SOC). Where acac is represented as pentane-2, 4-dione; tmd as 2,2,6,6-tetramethylheptane-3,5-dione; pic as pyridine-2-carboxylate; TTIQ as 1-thieno[3,2-b]thiophen-2-ylisoquinoline; CFM as 2-(4-fluorobrobenyl)-4-methylpyridine. A series of heteroleptic cyclometalated Ir (III) complexes, which are used for OLED application, were investigated by DFT and TD-DFT method. The frontier molecular orbital character and charge transfer character shown that they have the advantages of low efficiency roll-off properties, which is a ‘stumbling block’ in the process of OLED solid-lighting’s development. Namely, means the materials will play an important role in the journey development of OLED.

DFT and TD-DFT study a series of blue and green iridium complexes with mesityl-phenyl-imidazole ligand

Abstract A series of blue and green-emitting phosphorescent heteroleptic cyclometalated Ir(III) complexes with mesityl-phenyl-imidazole Ligand for organic light-emitting devices are investigated theoretically to explore their electronic structures, spectroscopic properties and the application value for organic light emitting devices. The geometries, electronic structures, lowest-lying singlet absorptions, and triplet emissions of Ir(mpim)3, and the theoretically designed models Ir(F-mpim)3, Ir(F2-mpim)3, (mpim)2Ir(acac), (F-mpim)2Ir(acac), (F2-mpim)2Ir(acac), (mpim)2Ir(tpip), (F-mpim)2Ir(tpip), (F2-mpim)2Ir(tpip), are investigated with Density Functional Theory (DFT) approaches, where mpim denotes 1-mesityl-2-phenyl-1H-imidazole, F-mpim denotes 2-(4-fluorophenyl)-1-mesityl-1H-imidazole, F2-mpim denotes 2-(2,4-difluorophenyl)-1-mesityl-1H-imidazole, acac denotes acetylacetonate, and tpip denotes tetraphenylimido-diphosphinate.

DFT/TDDFT investigation on the photophysical properties of a series of phosphorescent cyclometalated complexes based on the benchmark complex FIrpic

ABSTRACTThe photophysical properties of four Ir(III) complexes have been investigated by means of the density functional theory/time-dependent density functional theory (DFT/TDDFT). The effect of the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption and phosphorescent properties has been studied. The theoretical calculation shows that the lowest-lying singlet absorptions for complexes 1–4 are located at 387, 385, 418 and 386 nm, respectively. For 1–4, the phosphorescence at 465, 485, 494 and 478 nm is mainly attributed to the LUMO → HOMO and LUMO → HOMO-1 transition configurations characteristics. In addition, ionisation potential (IP), electron affinities (EAs) and reorganisation energy have been investigated to evaluate the charge transfer and balance properties between hole and electron. The balance of the reorganisation energies for complex 3 is better than others. The difference between hole transport and electron transport for complex 3 is the smallest among these complexes, which is beneficial to achieve the hole and electron transfer balance in emitting layer.

DFT/TDDFT investigation on the electronic structures and photophysical properties of a series of substituted N-heterocyclic carbene (NHC) platinum(II) complexes

The electronic and photophysical properties of a series of substituted N-heterocyclic carbene (NHC) platinum(II) complexes have been investigated by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The lowest-lying singlet absorptions for complexes 2–5 are attributed to the configurations of HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital). The emission energies for these complexes are obviously red-shifted in contrast to that of 1. For 3 and 4, the emission energies are nearly the same, consistent with their same energy gaps between of LUMO and HOMO. In addition, ionization potential (IP), electron affinities (EA) and reorganization energy (λ) also were obtained to evaluate the charge transfer and balance properties between hole and electron. From the calculated results, it can be seen that the complex 3 possesses possibly the largest kr value among these complexes due to the lowest ΔES1−T1, larger 3MLCT contribution, and higher μS1⁡ value. It is anticipated that this study could provide useful information for the synthesis of efficient platinum(II) phosphors in OLEDs.

Theoretical study on a series of iridium complexes with low efficiency roll-off property

A series of heteroleptic cyclometalated Ir (III) complexes for OLEDs application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, electronic structures, and the lowest-lying singlet absorptions and triplet emissions of (piq)2Ir(acac) (labeled 1) and theoretically designed models (piq)2Ir(dpis) (labeled 2), (4Fpiq)2Ir(dpis) (labeled 3), (4F5M-piq)2Ir(dpis) (labeled 4), (4,5-2F-piq)2Ir(dpis) (labeled 5) and (5-F-piq)2Ir(dpis) (labeled 6) were investigated with density functional theory (DFT)-based approaches, where, piq=1-phenylisoquinolato, acac=acetylacetonate and dpis=diphenylimidodisilicate. Their structures in the ground and excited states have been optimized at the DFT/B3LYP/LANL2DZ and TDDFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. Furthermore, the energy-transfer mechanism of these complexes also be analyzed here, and the result shown that the complexes 1–6 are having the low efficiency roll-off property. Except that, the oscillator strength analyze shown that the complexes 2–6, which were designed by theory, are suitable for OLED since their high oscillator strength property.

Theoretical Studies on Phosphorescent Materials: The Conjugation-Extended PtII Complexes

A theoretical study on the PtII complex A based on a dimesitylboron (BMes2)-functionalized [Pt(C^N)(acac)] (C^N = 2-phenyl-pyridyl, acac = acetylaceton) complex, as well as three conjugation-extended analogues of the methylimidazole (C*) ligand BMes2-[Pt(C^C*)(acac)] complexes B–D is performed. Their theoretical geometries, electronic structures, emission properties, and the radiative decay rate constants (kr) were also investigated. The energy differences between the two highest occupied orbitals with dominant Pt d-orbital components (Δddocc) of D both at the ground and excited states are the smallest of all. Compared with B, the charge transfer in D possesses a marked trend towards the extended conjugated group, while C changed inconspicuously. The lowest-lying absorptions and the phosphorescence of them can be described as a mixed metal-to-ligand charge transfer (MLCT)/intra-ligand π→π* charge transfer (ILCT) and 3MLCT/3ILCT, respectively. The variation of charge transfer properties induced by extended conjugation and the radiative decay rate constants (kr) calculated revealed that D is a more efficient blue phosphorescence material with a 497 nm emission transition.

Theoretical Studies on the Electronic Structures and Spectral Properties of Three Iridium(III) Complexes With Different NˆN Ligands

We report a quantum chemical study of the electronic structures and spectral properties of three iridium(III) biscarbene complexes with different heteroleptic N^N ligands. The theoretical calculation reveals that the lowest-lying singlet absorptions at 434 nm for 1 and 487 nm for 3 are attributed to the mixed transition characters of metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT). However, for 2, the lowest-lying singlet absorption at 509 nm is attributed to the MLCT. For 1–3, the phosphorescence at 739, 913, and 737 nm are mainly attributed to 3MLCT and 3LLCT characters. For 1 and 3, the emission energies are nearly the same, which is larger than that of 2. Ionization potentials (IP) and electron affinities (EA) calculations show that the assumed complex 3 has large EA value and enhanced electron injection ability as compared to complexes 1 and 2. Moreover, the reasons for different transition characters and phosphorescence quantum yield for the three complexes have been discussed in this paper. This theoretical contribution allows the factors determining the efficiency of radiative and nonradiative decay pathways in the three complexes.

Theoretical studies on the electronic structures and optical properties of the thiophene oligomer containing 2-(trifluoromethyl) thieno [3, 4-b] thiophene moiety and the CF3 end-caps

Structural, electronic, and optical properties of a series of π-conjugated thiophene oligomers P1-P3 and CF3P1-CF3P3 have been theoretically investigated. P1-P3 contain the 2- (trifluoromethyl) thieno [3, 4-b] thiophene moiety as the centre and 1–3 repeating thiophene units adjacent to its two sides respectively, while their corresponding derivatives CF3P1-CF3P3 with the CF3 as end-caps. The geometric structures of the oligomers in the ground and excited state were optimized by PBE1PBE and CIS methods with 6–31G (d) basis sets, respectively. All the oligomers exhibit zigzag arrangements. The absorptions and emissions were calculated by the time-dependent density functional theory method (TD-PBE1PBE). The lowest-lying absorptions of all the oligomers can be characterized as π-π* electron transition. For each series of oligomers, there is a progressive lowering in HOMO-LUMO gap with the increase of the repeating unit, being consistent with the red-shifted trend in the lowest-lying absorption and fluorescence from P1 to P3 and CF3P1 to CF3P3. To compare the P- and corresponding CF3P-oligomers, the end-cap CF3 group causes the slight blue shifts in absorption and emission spectra. The ionization potentials (IPS), electron affinities (EAs), and reorganization energies (λ) as well as the hole/electron extraction energies (HEP/EEP) of the oligomers were explored and those of the corresponding polymer were obtained by extrapolation method. The IP and HEP of P-polymer are lower than those of CF3P-polymer, indicating that the P-polymer is more suitable for hole transport than CF3P-polymer, while the higher EA and EEP for CF3P-polymer suggest the better electron transfer property. For CF3 end-caps, the CF3P-polymer exhibits the equal reorganization energy between electron and hole, which is a precondition for the charge transfer balance.

Efficient Blue-Emitting Ir(III) Complexes with Phosphine Carbanion-Based Ancillary Ligand: A DFT Study

We report a theoretical study on a series of heteroleptic cyclometalated Ir(III) complexes for OLED application. The geometries, electronic structures, and the lowest-lying singlet absorptions and triplet emissions of [(fppy)(2)Ir(III)(PPh(2)Np)] (1), and theoretically designed models [(fppy)(2)Ir(III)(PH(2)Np)] (2) and [(fppy)(2)Ir(III)Np](-)(3) were investigated with density functional theory (DFT)-based approaches, where, fppyH = 4-fluorophenyl-pyridine and NpH = naphthalene. The ground and excited states were, respectively, optimized at the M062X/LanL2DZ;6-31G* and CIS/LanL2DZ:6-31G* level of theory within CH(2)Cl(2) solution provided by PCM. The lowest absorptions and emissions were evaluated at M062X/Stuttgart;cc-pVTZ;cc-pVDZ level of theory. Though the lowest absorptions and emissions were all attributed as the ligand-based charge-transfer transition with slight metal-to-ligand charge-transfer transition character, the subtle differences in geometries and electronic structures result in the different quantum yields and versatile emission color. The newly designed molecular 3 is expected to be highly emissive in deep blue region.

Theoretical Studies on Structures and Spectroscopic Properties of Highly Efficient Phosphorescent [Ru(terpy)(phen)X]+ Complexes

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of three mixed-ligand Ru(II) complexes [Ru(terpy)(phen)X]+ (terpy=2,2′,6′,2″-terpyridine, phen=1,10-phenanthroline, and X=—C≡CH (1), X=Cl (2), X=CN (3)) were investigated theoretically using the density functional theory method. The ground and excited state geometries have been fully optimized at the B3LYP/LanL2DZ and UB3LYP/LanL2DZ levels, respectively. The absorption and emission spectra of the complexes in CH3CN solutions were calculated by time-dependent density functional theory with the PCM solvent model. The calculated bond lengths of Ru—C, Ru—N, and Ru—Cl in the ground state agree well with the corresponding experimental results. The highest occupied molecular orbital were dominantly localized on the Ru atom and monodentate X ligand for 1 and 2, Ru atom and terpy ligand for 3, while the lowest unoccupied molecular orbital were π* (terpy) type orbital. Therefore, the lowest-energy absorptions of 1 and 2 at 688 and 631 nm are attributed to a dyz (Ru)+π/p(X)→π* (terpy) transition with MLCT/XLCT (metal-to-ligand charge transfer/X ligand to terpy ligand charge transfer) character, whereas that of 3 at 529 nm is related to a dyz(Ru)+π(terpy)→π*(terpy) transition with MLCT and ILCT transition character. The calculated phosphorescence of three complexes at 1011 nm (1), 913 nm (2), and 838 nm (3) have similar transition properties to that of the lowest-lying absorption. It is shown that the lowest lying absorptions and emissions transition character of these Ru(II) complexes can be tuned by changing the electron-withdrawing ability of the monodentate ligand.

Ligand Effects on Structures and Spectroscopic Properties of Pyridine-2-aldoxime Complexes of Re(CO)3+: DFT/TDDFT Theoretical Studies

The series of novel rhenium(I) tricarbonyl mixed-ligand complexes Re(X)(CO)(3)(N^N) (N^N = pyridine-2-aldoxime; X = -Cl, 1; X = -CN, 2; and X = -C≡C, 3) has been investigated theoretically to explore the ligand X effect on their electronic structures and spectroscopic properties. The contribution of the X ligand to the highest occupied molecular orbital (HOMO) and HOMO-1 decreases in the order of 3 > 1 > 2, in line with the π-donating abilities of the X: -C≡C > -Cl > -CN. The reorganization energy (λ) calculations show that 1 and 3 will result in the higher efficiency of organic light-emitting diodes than 2. The lowest-lying absorptions of 1 and 3 can be assigned to the {[d(xz), d(yz)(Re) + π(CO) + π(X)] → [π* (N^N)]} transition with mixing metal-to-ligand, ligand-to-ligand, and X ligand-to-ligand charge transfer (MLCT/LLCT/XLCT) character, whereas this absorption at 354 nm (H-1 → L) of 2 is assigned to {[d(xz), d(yz)(Re) + π(CO) + π(N^N)] → [π* (N^N)]} transition with MLCT/LLCT/ILCT (intraligand charge transfer). Furthermore, the absorptions are red-shifted in the order 2, 1, and 3, with the increase of π-donating abilities of X ligands. The solvent effects cause red shifts of the absorption and emission spectra with decreasing solvent polarity.

Structures and Spectroscopic Properties of [Ru(iph)(L)<sub>2</sub>]<sup>2+</sup> (L=cpy, mpy, npy) Complexes Containing Tetradentate Ligands

采用密度泛函的B3LYP和UB3LYP方法分别优化了一系列[Ru（iph）（L）2]2＋（L=cpy（1）,mpy（2）,npy（3）;其中iph为2,9-双（1′-甲基-2′-咪唑）-1,10-邻二氮杂菲,cpy为4-氰基嘧啶,mpy为4-甲基嘧啶,npy为4-氮二甲基嘧啶）配合物的基态和激发态结构.利用含时密度泛函理论（TD-DFT）方法,结合极化连续介质（PCM）模型计算了它们在丙酮溶液中的吸收和发射光谱.研究结果表明：优化得到的几何结构参数和相应的实验值符合得非常好.1和2的最高占据分子轨道主要由金属的d轨道和iph配体的π轨道构成,但是3主要占据在npy配体上,而它们的最低空轨道主要由iph配体的π反键轨道占据.因此,1和2的最低能吸收和发射属于金属到配体（MLCT）和配体内部（ILCT）的电荷转移跃迁,而3属于两个配体之间的电荷转移（LLCT）跃迁.三个配合物的最低能吸收分别在509nm（1）,527nm（2）和563nm（3）,其磷光发射分别在683nm（1）,852nm（2）和757nm（3）.这显示出通过调节L配体的π电子给予能力可以改变最低能吸收和发射的跃迁性质和发光颜色.

Theoretical studies on structures and spectroscopic properties of 10-hydroxybenzo[h]quinoline zinc(II) and its derivatives substituted by cyano-groups

The geometric structures of 10-hydroxybenzo[h]quinoline zinc [Zn(BQ) 2] complex and its derivatives substituted by cyano-groups in the ground state and the lowest singlet excited state were optimized by B3LYP and ab initio CIS methods at LanL2DZ level, respectively. The absorption and emission spectra of these complexes were investigated by the time-dependent density functional theory (TD-DFT) level with PCM model on the basis of the optimized ground and excited states geometries, respectively. The calculated lowest-lying absorptions of all complexes were attributed to ILCT transitions mainly. The calculated emissions of complexes can be described as originated from an excited state with ILCT character mainly. The calculated results showed that the absorption and emission maximums could be tuned by changing the site of the substitutions. The Zn(BQ) 2 and its derivatives substituted by cyano-groups were potential electroluminescent materials with blue, green and yellow light emission.

Theoretical study on photophysical properties of angular-shaped mercury(II) bis(acetylide) complexes as light-emitting materials

Abstract An in-depth investigation on the optical and electronic properties of a series of mercury-containing and metal-free arylacetylenes with bridged heteroatoms was provided here. The geometric and electronic structures of the complexes in the ground state are studied with density functional theory and Hartree–Fock, whereas the lowest singlet and triplet excited states are optimized by singles configuration interaction (CIS) methods. At the time-dependent density functional theory (TD-DFT) level, molecular absorptions and emission properties were calculated on the basis of optimized ground- and excited-state geometries, respectively. The calculated lowest-lying absorptions of the investigated complexes are attributed to ligand-to-ligand charge transfer (LLCT), intraligand (IL) and ligand-to-metal charge transfer (LMCT). The results show that the optoelectronic properties for the complexes are affected by the transition-metal atom, various bridge heteroatoms and different end-group substituents. Moreover, the calculated data reveal that the studied molecules have improved charge-transfer rate, especially for designed molecules.

DFT/TD‐DFT investigation on Ir(III) complexes with N‐heterocyclic carbene ligands: Geometries, electronic structures, absorption, and phosphorescence properties

Iridium(III) complexes with N-heterocyclic (NHC) ligands including fac-Ir(pmb)(3) (1), mer-Ir(pmb)(3) (2), (pmb)(2)Ir(acac) (3), mer-Ir(pypi)(3) (4), and fac-Ir(pypi)(3) (5) [pmb = 1-phenyl-3H-benzimidazolin-2-ylidene, acac = acetoylacetonate, pypi = 1-phenyl-5H-benzimidazolin-2-ylidene; fac = facial, mer = meridional] were investigated theoretically. The geometry structures of 1-5 in the ground and excited state were optimized with restricted and unrestricted DFT (density functional theory) methods, respectively (LANL2DZ for Ir atom and 6-31G for other atoms). The HOMOs (highest occupied molecular orbitals) of 1-3 are composed of d(Ir) and pi(phenyl), while those of 4 and 5 are contributed by d(Ir) and pi(carbene). The LUMOs (lowest unoccupied molecular orbitals) of 1, 2, 4, and 5 are localized on carbene, but that of 3 is localized on acac. The calculated lowest-lying absorptions with TD-DFT method based on Perdew-Burke-Erzenrhof (PBE) functional of 1 (310 nm), 2 (332 nm), and 3 (347 nm) have ML(carbene)CT/IL(phenyl-->carbene)CT (MLCT = metal-to-ligand charge transfer; ILCT = intraligand charge transfer) transition characters, whereas those of 4 (385 nm) and 5 (389 nm) are assigned to ML(carbene)CT/IL(carbene-->carbene)CT transitions. The phosphorescences calculated by TD-DFT method with PBE0 functional of 1 (386 nm) and 2 (388 nm) originate from (3)ML(carbene)CT/(3)IL(phenyl-->carbene)CT excited states, but those of 4 (575 nm) and 5 (578 nm) come from (3)ML(carbene)CT/(3)IL(carbene-->carbene)CT excited states. The calculated results showed that the carbene and phenyl groups act as two independent chromophores in transition processes. Compared with 1 and 2, the absorptions of 4 and 5 are red-shifted by increasing the effective pi-conjugation groups near the C(carbene) atom. We predicated that (pmb)(2)Ir(acac) is nonemissive, because the LUMO of 3 is contributed by the nonemissive acac ligand.

Theoretical studies on electronic structures, spectra and charge transporting properties of a series of Pt(C ΛN) 2 complexes

We report a quantum-chemical study of electronic, optical and charge transporting properties of four platinum (II) complexes, Pt(C ΛN) 2 (C ΛN = phenylpyridine or thiophenepyridine). The lowest-lying absorptions at 442, 440, 447 and 429 nm are all attributed to the mixed transition characters of metal-to-ligand charge transfer (MLCT) and ligand-centered (LC) π → π* transition. While, unexpectedly, the lowest-lying phosphorescent emissions at 663, 660, 675 and 742 nm are mainly from metal-to-ligand charge transfer ( 3MLCT) ligand-centered (LC) π → π* transition. Ionization potential (IP), electron affinities (EA) and reorganization energy ( λ hole/electron) were obtained to evaluate the charge transfer and balance properties between hole and electron. The calculated results reveal that the small structure changes of the charged states relative to the neutral ones, and the smaller IP and EA values indicate that they exhibit a relatively high structural stability versus the injection of one charge and have better holes than electron-injection abilities. The smaller λ values and the smaller differences (within 0.06 eV) between λ hole and λ electron indicate the better transfer balance between holes and electrons. Moreover, the attached methyl groups slightly improve the hole-injection ability and deduce the electron-injection ability. The strong phosphorescence emission and the favorable transporting properties compared with other reported complexes indicate their potential applications in as emitters OLEDs.

Electronic structures and optical properties of neutral substituted fluorene-based cyclometalated platinum(II)–acetylide complexes: A DFT exploration

We report a combinational DFT and TD-DFT study of the electronic and optical properties of several tridentate cyclometalated mononuclear [Pt(C^N^N)(CCR)] (1–3), [Pt(C^N^N)(CCRCCH)] (4), and dinuclear [Pt(C^N^N)(CCRCC)Pt(C^N^N)] (5 (C2 symmetry) and 5′ (Cs symmetry)) platinum(II) complexes with σ-acetylide ligand bearing fluorene substituents, where HC^N^N = 6-aryl-2,2′-bipyridine, R = fluorene-2,7-diyl 1, 4, 5 and 5′, R = 9,9-dimethylfluorene-2,7-diyl 2, R = 9,9-diethylfluorene-2,7-diyl 3. The structural and electronic properties of the ground- and lowest triplet state and the EA and IP values of the complexes are discussed. It is found that all of the lowest-lying absorptions are categorized as the LLCT combined with the MLCT transitions. The oscillator strengths of the lowest energy absorptions get a remarkable enhancement for the dinuclear complexes 5 and 5′compared to 1–4 due to the increase of electronic delocalization on the more planar molecular geometry. In general, the phosphorescent emissions of these complexes in CH2Cl2 are the reverse process of their lowest energy absorption transitions, except that of 4 is assigned as 3[π∗−π]/3MLCT transition because of the strengthened electronic localization effect and the interaction with the solvent in the lowest triplet state. In addition, these complexes hold promise as a new kind of nonlinear optical material owing to their large static first hyperpolarizabilities (β0). The β0 value has increased in the dinuclear complexes in contrast to those of the mononuclear ones owing to their larger transition moment and smaller transition energy.

Different electronic structures and spectroscopic properties of cationic [M(ppy)2(N∧N)]+ (M = Rh, Ir; N∧N = Hcmbpy, H2dcbpy), a DFT study

We report a comparative quantum-chemical study of the electronic structures and optical properties of a series of cationic complexes [M(ppy)(2)(N--N)](+) (N--N = Hcmbpy = 4-carboxy-4'-methylbpy, M = Rh (Rh1), Ir(Ir2); N--N = H(2)dcbpy = 4,4'-dicarboxy-bpy, M = Rh (Rh3) and Ir (Ir4)). The theoretical calculation reveals that the increased number of -COOH groups on the bpy ligand can decrease the energy levels of LUMO more than HOMO and narrow down the HOMO-LUMO energy gaps, which results in the red-shifted of the lowest-lying absorption and phosphorescent spectra. The lowest-lying singlet absorptions were categorized as d(M,M = Rh or Ir) + pi(ppy) -->pi*(bpy) with MLCT and LLCT characters. The calculated phosphorescence at 628 and 668 nm for and is mainly bpy-based intraligand pi* -->pi transition, while 743 and 827 nm emission for and are mixed characters of (3)MLCT and (3)LLCT {[pi*(bpy)] --> [d(Ir) + pi(ppy)]}. Moreover, the reasons for different transition characters and phosphorescence quantum yield between Rh and Ir species, and between and are discussed in this paper.

Theoretical studies on the optical properties and substituent effects of osmium (II) complexes Os(N^N)(C [tbnd]N) 2(PH 3) 2

The ground and the excited state geometries, electronic structures, absorption and emission spectra as well as the substituent effects of a series of osmium (II) diimine complexes Os(N^N)(C N)2(PH3)2 [N^N = 2,2′−bipyridine (bpy) 1; 4,4-di- tert-butyl-2,2′-bipyridine (dbubpy) 2; 4,4-di-methoxy-2,2′-bipyridine (dmobpy) 3; 4,4-di-chloro-2,2′-bipyridine (dcbpy) 4] were investigated by DFT and ab initio methods. At the TD-DFT and PCM level, the lowest-lying absorptions of 1− 4 at 483, 467, 463, and 522 nm are dominantly assigned to a {[d xy(Os)] → [π*(N^N)]} transition with MLCT character. The calculated phosphorescence of 1− 4 at 635, 605, 598, and 683 nm can be described as originating from 3{[d xy(Os)] [π*(N^N)]} excited state. The spectra are blue-shifted by adding electron-donating substituents of t−butyl and OCH3 on the N^N ligands, but red-shifted by adding electron-withdrawing group Cl.

Mechanism of Ir(ppy)2(N^N)+ (N^N = 2-Phenyl-1H-imidazo[4,5-f][1,10]phenanthroline) Sensor for F−, CF3COOH, and CH3COO−: Density Functional Theory and Time-Dependent Density Functional Theory Studies

The geometries, electronic structures, and spectroscopic properties of Ir(ppy)2(N--N)(+) (1) (N--N = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline, ppy = 2-phenylpyridine), Ir(ppy)2(N--N)(+) x F(-) (2), Ir(ppy)2(N--N)(+) x CF3COOH (3/3a), and Ir(ppy)2(N--N)(+) x CH3COO(-) (4) were investigated theoretically. The ground and the excited state geometries of 1-4 were optimized at the B3LYP/LANL2DZ and UB3LYP/LANL2DZ levels, respectively. The optimized geometries agree well with the corresponding experimental results. The HOMOs of 1-4 and 3a are composed of pi(ppy) and d(Ir), and the LUMOs of 1, 2, 3a, and 4 are contributed by pi*(N--N), whereas the LUMO of 3 is composed of pi*(N--N) and pi*(CF3COOH). Under the time-dependent density functional theory level with polarized continuum model model, the absorption and phosphorescence in CH2Cl2 media were calculated on the basis of the optimized ground and excited state geometries, respectively. The lowest-lying absorptions of 1 (412 nm) and 3/3a (409/419 nm) have MLCT/LLCT transition characters, and those of 2 (448 nm) and 4 (427 nm) are contributed by ILCT character. The calculated lowest-energy triplet excited states responsible for phosphorescence of 1 (519 nm) and 3/3a (661/702 nm) have mixing (3)MLCT/(3)LLCT/(3)ILCT characters, but those of 2 and 4 only have (3)ILCT but without (3)MLCT character, which is the reason for the no-emissive character of 2 and 4. Moreover, the phosphorescence character of 3 is hardly changed by different addition sites of CF3COOH group (3a). The calculated results also showed that complex 1 is more suitable for an F(-) sensor than for CF3COOH and CH3COO(-) sensors.