Deactivation pathways for metal-to-ligand charge-transfer excited states of ruthenium polypyridyl complexes with triphenylphosphine as a ligand

Emission, excitation spectra, quantum yields, and emission lifetimes are reported for the mixed-ligand, bis(2.2'-bipyridine)ruthenium(II) complexes, cis-[Ru(bpy)(2)(PPh(3))X](n+) with X = Cl(-), Br(-), CN(-), and NO(2)(-) (n = 1) and pyridine (py), 4-aminopyridine (NH(2)py), 4,4'- bipyridine (4,4'-bpy), NH(3), and MeCN (n = 2) in EtOH-MeOH, 4:1 (v:v), at 77 K. Radiative, k(r), and nonradiative, k(nr), decay rate constants were determined for the series of complexes, and a linear dependence of ln k(nr) on E(00), with E(00) being the 0-0 energy gap determined by emission spectral fitting, was obtained with a slope of -(0.6 ± 0.1) × 10(-3). On the basis of emission quantum yields and apparent k(r) values, possible metal-to-ligand charge-transfer (MLCT) deactivation by direct population of excited (1)dd states from initially excited (1)MLCT states is discussed.     

Photophysics and nonlinear absorption of cyclometalated 4,6-diphenyl-2,2'-bipyridyl platinum(II) complexes with different acetylide ligands

The photophysical properties of a series of 4,6-diphenyl-2,2'-bipyridyl platinum(II) complexes bearing different σ-alkynyl ancillary ligands (1a-1k) were systematically investigated. All complexes exhibit strong (1)π,π* absorption bands in the UV region; and broad, structureless charge-transfer band(s) in the visible region, which systematically red-shift(s) when the electron-donating ability of the para substituent on the phenylacetylide ligand increases. All complexes are emissive in solution at room temperature. When excited at the charge-transfer absorption band, the complexes exhibit long-lived orange emission (λ(max): 555-601 nm), which is attributed to a triplet metal-to-ligand charge transfer/intraligand charge transfer emission ((3)MLCT/(3)ILCT). Most of these complexes exhibit broad triplet transient difference absorption in the visible to the near-IR region, with a lifetime comparable to those measured from the decay of the (3)MLCT/(3)ILCT emission. The reverse saturable absorption (RSA) of these complexes were demonstrated at 532 nm using nanosecond laser pulses. The degree of RSA follows this trend: 1k ≈ 1a > 1c > 1f ≈ 1i > 1h ≈ 1b > 1e > 1d > 1g, which is mainly determined by the ratio of the triplet excited-state absorption cross section to that of the ground-state and the triplet excited-state quantum yield.     

Effect of Delocalization and Rigidity in the Acceptor Ligand on MLCT Excited-State Decay

In its most simple form, the energy gap law for excited-state nonradiative decay predicts a linear dependence of ln k(nr) on the ground- to excited-state energy gap, where k(nr) is the rate constant for nonradiative decay. At this level of approximation, the energy gap law has been successfully applied to nonradiative decay in a wide array of MLCT excited states of polypyridyl complexes of Re(I), Ru(II), and Os(II). This relationship also predicts a dependence of k(nr) on the structural characteristics of the acceptor ligand. We report here a brief survey of the literature which suggests that such effects exist and have their origin in the extent of delocalization of the excited electron in the ligand pi framework and on acceptor ligand rigidity.     

One-photon photophysics and two-photon absorption of 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes

The synthesis, one-photon photophysics and two-photon absorption (2PA) of three dipolar D-π-A 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2'-terpyridine and their platinum chloride complexes with different linkers between the donor and acceptor are reported. All ligands exhibit (1)π,π* transition in the UV and (1)π,π*/(1)ICT (intramolecular charge transfer) transition in the visible regions, while the complexes display a lower-energy (1)π,π*/(1)CT (charge transfer) transition in the visible region in addition to the high-energy (1)π,π* transitions. All ligands and the complexes are emissive at room temperature and 77 K, with the emitting excited state assigned as the mixed (1)π,π* and (1)CT states at RT. Transient absorption from the ligands and the complexes were observed. 2PA was investigated for all ligands and complexes. The two-photon absorption cross-sections (σ(2)) of the complexes (600-2000 GM) measured by Z-scan experiment are much larger than those of their corresponding ligands measured by the two-photon induced fluorescence method. The ligand and the complex with the ethynylene linker show much stronger 2PA than those with the vinylene linker.     

Nonlinear Absorbing Platinum(II) Diimine Complexes: Synthesis, Photophysics, and Reverse Saturable Absorption

A series of platinum(II) diimine complexes with different substituents on fluorenyl acetylide ligands (1?a-1?e) were synthesized and characterized. The influence of the auxiliary substituent on the photophysics of these complexes has been systematically investigated spectroscopically and theoretically (using density functional theory (DFT) methods). All complexes exhibit ligand-centered (1) π,π* transitions in the UV and blue spectral region, and broad, structureless (1) MLCT/(1) LLCT (1?a, 1?b, 1?d and 1?e) or (1) MLCT/(1) LLCT/(1) π,π* (1?c) absorption bands in the visible region. All complexes are emissive in solution at room temperature, with the emitting state is tentatively assigned to mixed (3) MLCT/(3) π,π* states. The degree of (3) π,π* and (3) MLCT mixing varies with different substituents and solvent polarities. Complexes 1?a-1?e exhibit relatively strong singlet and triplet transient absorption from 450 to 800?nm, at which point reverse saturable absorption (RSA) could occur. Nonlinear transmission experiments at 532?nm by using nanosecond laser pulses demonstrate that 1?a-1?e are strong reverse saturable absorbers and could potentially be used as broadband nonlinear absorbing materials.     

Enhanced deep-red luminescence of tris(hexafluoroacetylacetonato)samarium(III) complex with phenanthroline in solution by control of ligand coordination

The effect of solvent molecule on the emission properties of Sm(hfa)3(phen)2 (hfa = hexafluoroacetylacetonato, phen = phenanthoroline) was investigated using acetone, acetonitrile, and pyridine. 5G(5/2) --> 5H(9/2) transition intensities in pyridine were found to be larger than those in corresponding acetone and acetonitrile. The radiative rate constant in pyridine (4.8 x 10(2) s(-1)) was 2 times larger than those in acetonitrile (2.6 x 10(2) s(-1)) and acetone (2.3 x 10(2) s(-1)), although the nonradiative transition via vibrational relaxation (k(nr) = 1.7 x 10(4) s(-1)) in pyridine was the same as those in acetone and acetonitrile (k(nr) = 1.8 x 10(4) s(-1)), resulting in the enhanced emission quantum yield of Sm(III) complex in pyridine (2.7%). The coordination structures of Sm(hfa)3(phen)2 in acetonitrile, acetone, and pyridine were estimated by X-ray single-crystal analyses. These results indicate that enhancement of the emission properties in pyridine is due to faster radiative rate related to formation of asymmetrical nine-coordinated structure, Sm(hfa)3(phen)(py) (py = pyridine).     

Synthetic control of excited-state properties in cyclometalated Ir(III) complexes using ancillary ligands

The synthesis and photophysical characterization of a series of (N,C(2')-(2-para-tolylpyridyl))2 Ir(LL') [(tpy)2 Ir(LL')] (LL' = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu)) are reported. A smaller series of [(dfppy)2 Ir(LL')] (dfppy = N,C(2')-2-(4',6'-difluorophenyl)pyridyl) complexes were also examined along with two previously reported compounds, (ppy)2 Ir(CN)2- and (ppy)2 Ir(NCS)2- (ppy = N,C(2')-2-phenylpyridyl). The (tpy)2 Ir(PPh2CH2)2 BPh2 and [(tpy)2 Ir(CN-t-Bu)2](CF3SO3) complexes have been structurally characterized by X-ray crystallography. The Ir-C(aryl) bond lengths in (tpy)2 Ir(CN-t-Bu)2+ (2.047(5) and 2.072(5) A) and (tpy)2 Ir(PPh2CH2)2 BPh2 (2.047(9) and 2.057(9) A) are longer than their counterparts in (tpy)2 Ir(acac) (1.982(6) and 1.985(7) A). Density functional theory calculations carried out on (ppy)2 Ir(CN-Me)2+ show that the highest occupied molecular orbital (HOMO) consists of a mixture of phenyl-pi and Ir-d orbitals, while the lowest unoccupied molecular orbital is localized primarily on the pyridyl-pi orbitals. Electrochemical analysis of the (tpy)2 Ir(LL') complexes shows that the reduction potentials are largely unaffected by variation in the ancillary ligand, whereas the oxidation potentials vary over a much wider range (as much as 400 mV between two different LL' ligands). Spectroscopic analysis of the cyclometalated Ir complexes reveals that the lowest energy excited state (T1) is a triplet ligand-centered state (3LC) on the cyclometalating ligand admixed with 1MLCT (MLCT = metal-to-ligand charge-transfer) character. The different ancillary ligands alter the 1MLCT state energy mainly by changing the HOMO energy. Destabilization of the 1MLCT state results in less 1MLCT character mixed into the T1 state, which in turn leads to an increase in the emission energy. The increase in emission energy leads to a linear decrease in ln(k(nr)) (k(nr) = nonradiative decay rate). Decreased 1MLCT character in the T1 state also increases the Huang-Rhys factors in the emission spectra, decreases the extinction coefficient of the T1 transition, and consequently decreases the radiative decay rates (k(r)). Overall, the luminescence quantum yields decline with increasing emission energies. A linear dependence of the radiative decay rate (k(r)) or extinction coefficient (epsilon) on (1/deltaE)2 has been demonstrated, where deltaE is the energy difference between the 1MLCT and 3LC transitions. A value of 200 cm(-1) for the spin-orbital coupling matrix element 3LC absolute value(H(SO)) 1MLCT of the (tpy)2 Ir(LL') complexes can be deduced from this linear relationship. The (fppy)2 Ir(LL') complexes with corresponding ancillary ligands display similar trends in excited-state properties.     

Spectroscopic and excited-state properties of tri-9-anthrylborane I: Solvent polarity effects

Spectroscopic and excited-state properties of tri-9-anthrylborane (TAB), showing unique absorption and fluorescence characteristics originating from p(boron)-pi(anthryl group) orbital interactions, were studied in 12 solvents. Although the absorption maximum energy (nu(a)) of TAB which appeared at around 21 x 10(3) cm(-1) (band I) was almost independent of the solvent polarity parameter, f(X) (f(X) = (D(s) - 1)/(2D(s) + 1) - (n(2) - 1)/(2n(2) + 1) where D(s) and n represent the static dielectric constant and the refractive index of a solvent, respectively), the fluorescence maximum energy (nu(f)) showed a linear correlation with f(X). The f(X) dependence of the value of nu(a) - nu(f) demonstrated that the change in the dipole moment of TAB upon light excitation was approximately 8.0 D, indicating that absorption band I was ascribed to an intramolecular charge-transfer transition in nature. The excited electron of TAB was thus concluded to localize primarily on the p orbital of the boron atom. Furthermore, it was shown that the fluorescence lifetime and quantum yield of TAB varied from 11.8 to 1.1 ns and from 0.41 to 0.02, respectively, with an increase in f(X). The present results indicated that the nonradiative decay rate constant (k(nr)) of TAB was influenced significantly by f(X). Excited-state decay of TAB was understood by intramolecular back-electron (charge) transfer from the p orbital of the boron atom to the pi orbital of the anthryl group, which was discussed in terms of the energy gap dependence of k(nr). Specific solvent interactions of TAB revealed by the present spectroscopic and photophysical studies are also discussed.     

Mechanism of NO photodissociation in photolabile manganese-NO complexes with pentadentate N5 ligands

The Mn-nitrosyl complexes [Mn(PaPy(3))(NO)](ClO(4)) (1; PaPy(3)(-) = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) and [Mn(PaPy(2)Q)(NO)](ClO(4)) (2, PaPy(2)Q(-) = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-quinoline-2-carboxamide) show a remarkable photolability of the NO ligand upon irradiation of the complexes with UV-vis-NIR light [Eroy-Reveles, A. A.; Leung, Y.; Beavers, C. M.; Olmstead, M. M.; Mascharak, P. K. J. Am. Chem. Soc. 2008, 130, 4447]. Here we report detailed spectroscopic and theoretical studies on complexes 1 and 2 that provide key insight into the mechanism of NO photolabilization in these compounds. IR- and FT-Raman spectroscopy show N-O and Mn-NO stretching frequencies in the 1720-1750 and 630-650 cm(-1) range, respectively, for these Mn-nitrosyls. The latter value for ν(Mn-NO) is one of the highest transition-metal-NO stretching frequencies reported to this date, indicating that the Mn-NO bond is very strong in these complexes. The electronic structure of 1 and 2 is best described as Mn(I)-NO(+), where the Mn(I) center is in the diamagnetic low-spin state and the NO(+) ligand forms two very strong π backbonds with the d(xz) and d(yz) orbitals of the metal. This explains the very strong Mn-NO bonds observed in these complexes, which even supersede the strengths of the Fe- and Ru-NO bonds in analogous (isoelectronic) Fe/Ru(II)-NO(+) complexes. Using time-dependent density functional theory (TD-DFT) calculations, we were able to assign the electronic spectra of 1 and 2, and to gain key insight into the mechanism of NO photorelease in these complexes. Upon irradiation in the UV region, NO is released because of the direct excitation of d(π)_π* → π*_d(π) charge transfer (CT) states (direct mechanism), which is similar to analogous NO adducts of Ru(III) and Fe(III) complexes. These are transitions from the Mn-NO bonding (d(π)_π*) into the Mn-NO antibonding (π*_d(π)) orbitals within the Mn-NO π backbond. Since these transitions lead to the population of Mn-NO antibonding orbitals, they promote the photorelease of NO. In the case of 1 and 2, further transitions with distinct d(π)_π* → π*_d(π) CT character are observed in the 450-500 nm spectral range, again promoting photorelease of NO. This is confirmed by resonance Raman spectroscopy, showing strong resonance enhancement of the Mn-NO stretch at 450-500 nm excitation. The extraordinary photolability of the Mn-nitrosyls upon irradiation in the vis-NIR region is due to the presence of low-lying d(xy) → π*_d(π) singlet and triplet excited states. These have zero oscillator strengths, but can be populated by initial excitation into d(xy) → L(Py/Q_π*) CT transitions between Mn and the coligand, followed by interconversion into the d(xy) → π*_d(π) singlet excited states. These show strong spin-orbit coupling with the analogous d(xy) → π*_d(π) triplet excited states, which promotes intersystem crossing. TD-DFT shows that the d(xy) → π*_d(π) triplet excited states are indeed found at very low energy. These states are strongly Mn-NO antibonding in nature, and hence, promote dissociation of the NO ligand (indirect mechanism). The Mn-nitrosyls therefore show the long sought-after potential for easy tunability of the NO photorelease properties by simple changes in the coligand.     

Luminescent square-planar platinum(II) complexes with tridentate 3-bis(2-pyridylimino)isoindoline and monodentate N-heterocyclic ligands

A series of platinum(II) complexes with 1,3-bis(2-pyridylimino)isoindoline (BPI) derivatives were prepared by substitution of the coordinated Cl in the precursor complex Pt(BPI)Cl with a N-heterocyclic ligand such as pyridine, phthalazine or phenanthridine. These complexes display orange to red luminescence in fluid dichloromethane solutions and in the solid states at room temperature. The photophysical properties were tuned by introducing electron-withdrawing -NO(2) or electron-donating -NH(2) to the BPI ligand. The DFT computational studies suggest that the emission in the N-heterocyclic ligand substituted platinum(II) complexes originates mainly from the (3)[π→π*(BPI)] (3)IL triplet excited state, mixed with some (3)[dπ(Pt)→π*(BPI)] (3)MLCT character. Compared with the precursor Pt(BPI)Cl, both the low-energy absorption and the emission in the N-heterocyclic ligand substituted platinum(II) complexes exhibits a distinct blue-shift due to an obviously enhanced contribution from the (3)IL state and a reduced (3)MLCT character.     

Theoretical studies on Ru(fppz)2(CO)L (L = N-heterocyclic ligand): Electronic structure, absorption, phosphorescence, and solvatochromism

A series of ruthenium(II) complexes Ru(fppz)₂(CO)L [fppz = 3-trifluoromethyl-5(2-pyridyl)pyrazole; L = pyridine (1), 4-dimethylaminopyridine (2), 4-cyanopyridine (3)] were designed and investigated theoretically to explore their electronic structures, absorption, and emissions as well as the solvatochromism. The singlet ground state and triplet excited state geometries were fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ level, respectively. The HOMO of 1–3 is composed of d_yz(Ru) atom and π(fppz). The LUMO of 1 and 2 is dominantly contributed by π*(fppz) orbital, but that of 3 is contribute by π*(L). Absorption and phosphorescence in vacuo, C₆H₁₂, and CH₃CN media were calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest-lying absorption of 1 and 2 at 387 and 391 nm is attributed to {[d_yz(Ru) + π(fppz)] → [π*(fppz)]} transition, but that of 3 at 479 nm is assigned to {[d_yz(Ru) + π(fppz)] → [π*(L)]} transition. The phosphorescence of 1 and 2 at 436 and 438 nm originates from ³{[d_yz(Ru) + π(fppz)] [π*(fppz)]} excited state, while that of 3 at 606 nm is from ³{[d_yz(Ru) + π(fppz)] [π*(L)]} excited state. The calculation results showed that the absorption and emission transition character can be changed from MLCT/ILCT to MLCT/LLCT transition by altering the substituent on the L ligand. The phosphorescence of 1 and 2 does not have solvatochromism, but that of 3 at 606 nm (vacuo), 584 nm (C₆H₁₂), and 541 nm (CH₃CN) is strongly dependent on the solvent polarity, so introducing electron-withdrawing group on ligand L will induce remarkable solvatochromism.     

Absorption Spectra and Photoreactivity of Para-aminobenzophenone by Time-dependent Density Functional Theory

The absorption spectral properties of para-aminobenzophenone (p-ABP) were investigated in gas phase and in solution by time-dependent density functional theory. Calculations suggest that the singlet states vary greatly with the solvent polarities. In various polar solvents, including acetonitrile, methanol, ethanol, dimethyl sulfoxide, and dimethyl formamide, the excited S1 states with charge transfer character result from π→π* transitions. However, in nonpolar solvents, cyclohexane, and benzene, the S1 states are the result of n→π* transitions related to local excitation in the carbonyl group. The excited T1 states were calculated to have ππ* character in various solvents. From the variation of the calculated excited states, the band due to π→π* transition undergoes a redshift with an increase in solvent polarity, while the band due to n→π* transition undergoes a blueshift with an increase in solvent polarity. In addition, the triplet yields and the photoreactivities of p-ABP in various solvents are discussed.     

联吡啶Ir(Ⅲ)配合物电子结构及光谱性质的理论研究

采用密度泛函理论(DFT)对配合物Ir(ppy)2(N^N)+ [ppy=2-phenylpyrine, N^N=bpy= 2,2’-bipyridine(1); N^N=H2dcbpy=4.4’-dicarboxy-2,2’-bipyridine(2), N^N=Hcmbpy=4-carboxy-4’-methyl-2,2’-bipyridine(3)] 的基态和激发态几何构型进行优化, 通过TDDFT/B3LYP方法得到这些化合物在乙腈溶液中的吸收光谱和磷光发射光谱及其跃迁性质. 研究结果表明, 化合物1 (384 nm), 2(433 nm)和3 (413 nm) 最低的吸收谱被指认为MLCT/LLCT[dIr+π(ppy)→π*(N^N)]电荷跃迁. 化合物1(486 nm), 2(576 nm)和3 (567 nm)最低的磷光发射可以描述为[dIr+π(ppy)]→[π*(N^N)]跃迁. 这是由于联吡啶配体上吸电子基团的引入, 稳定了相应的空轨道, 导致了化合物2和3的吸收和发射光谱红移. 同时, 化合物非线性光学性质的计算结果表明, 三种化合物均具有较大的一阶超极化率(β), 联吡啶配体中吸电子基团的增加, 使得分子内电子转移增强, 导致一阶超极化率增大.     

Luminescent cyclometalated dialkynylgold(III) complexes of 2-phenylpyridine-type derivatives with readily tunable emission properties

A novel class of luminescent dialkynylgold(III) complexes containing various phenylpyridine and phenylisoquinoline-type bidentate ligands has been successfully synthesized and characterized. The structures of some of them have also been determined by X-ray crystallography. Electrochemical studies demonstrate the presence of a ligand-centered reduction originating from the cyclometalating C^N ligand, whereas the first oxidation wave is associated with an alkynyl ligand-centered oxidation. The electronic absorption and photoluminescence properties of the complexes have also been investigated. In dichloromethane solution at room temperature, the low-energy absorption bands are assigned as the metal-perturbed π-π* intraligand (IL) transition of the cyclometalating C^N ligand, with mixing of charge-transfer character from the aryl ring to the pyridine or isoquinoline moieties of the cyclometalating C^N ligand. The low-energy emission bands of the complexes in fluid solution at room temperature are ascribed to originate from the metal-perturbed π-π* IL transition of the cyclometalatng C^N ligand. For complex 4 that contains an electron-rich amino substituent on the alkynyl ligand, a structureless emission band, instead of one with vibronic structures as in the other complexes, was observed, which was assigned as being derived from an excited state of a [π(C≡CC(6) H(4) NH(2) )→π*(C^N)] ligand-to-ligand charge-transfer (LLCT) transition.     

Synthesis,spectral, DFT calculations and biological studies of solvatochromic copper(II)-ONS hydrazone derived from 2-aminochromone-3-carboxaldehyde

New ONS hydrazone ligand, 2-[(2-aminochromon-3-yl)methylidene]-N-phenylhydrazinecarbothioamide, HL , was synthesized and reacted with different salts of Cu (II) ion (OAc⁻, NO₃⁻, SO₄²⁻ and Cl⁻) in absence and presence of secondary ligands (L′); 8-hydroxyquinoline, 1,10-phenanthroline or SCN⁻; to form binary and ternary Cu(II)-chelates. The ligand and its Cu(II)-complexes were fully characterized by analytical, spectral, thermal, conductivity and magnetic susceptibility measurements. The metal chelates showed octahedral, square planar and /or distorted tetraherdal arrangements. Coats–Redfern equations used to calculate the kinetic parameters of the thermal decomposition stages (E_a, A, ΔH, ΔS and ΔG). The compounds exhibit luminescence property; promising interesting potential applications as photoactive materials. Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet and microscopic solvent polarity parameter and E_T^N correlation methods were applied on the solvatochromic shifts of emission spectra to evaluate the ground (μ_g) and excited (μ_e) states dipole moments. Excited state dipole moment is larger than the ground state which may be attributed to π-π* transition. The coordinating anions play an important role on the position and intensity of emission band. The ligand and its metal complexes showed antimicrobial activity towards Gram–positive bacteria, Gram–negative bacteria, yeast and fungus. The molecular structural parameters of HL and its Cu(II)- complexes have been calculated on the basis of DFT engaged in the Gaussian 09 program at the B3LYP/6-31G(d,p) level; the theoretical data are correlated with the experimental data.     

[Au(PH3)]+修饰的芳香基炔基配合物发光机制的从头计算研究

用从头计算法研究H3PAuC≡CPh(a), H3PAu(C≡C-1,4-C6H4)Ph(b)和H3PAu(C≡C-1,4-C6H4)C≡CPh(c) 3种Au(Ⅰ)配合物的磷光发光性质, 使用MP2和CIS方法分别优化配合物的基态和激发态的几何结构. 计算结果表明, 激发态的电子跃迁减弱了Au与配体的成键作用. 由计算得出3种Au(Ⅰ)配合物的最低能量磷光发射光谱分别为530, 610和615 nm, 皆由A3A′→1A′产生, 属于Au(6p)→C(2p)的电荷转移(MLCT)修饰下的pπ*(C≡C, )→pπ(C≡C, )跃迁本质, 并伴有Au(6p)→Au(5d)的金属中心电荷转移(MCCT)性质. 随着分子增长, 其激发态轨道中Au的p轨道成分减少, 相应的最低能量磷光发射的波长红移.     

三联吡啶Pt(Ⅱ)配合物的基态和激发态的理论研究

为了探究取代基对三联吡啶Pt(Ⅱ)配合物发光性质的影响, 采用MP2和CIS方法分别对配合物[Pt(trpy)C≡CC6H4R]+[trpy=2,2',6',2″-Terpyridine; R=NO2(1), Cl(2), H(3), CH3(4)]的基态和激发态的几何构型进行了优化, 通过TDDFT/B3LYP方法得到了这些化合物在二氯甲烷溶液中的磷光发射光谱以及它们的跃迁性质. 研究结果表明, 由于NO2的强吸引作用以及在C≡CC6H4NO2部分可能存在的电子共振结构, 化合物1的最低发射可以指认为Pt—C≡C→trpy(3MLCT/3LLCT) 的跃迁, 并且还有很大的一部分来自于π→π*(C6H4NO2) 跃迁的贡献, 而化合物3和化合物4由于含有给电子基团, 因此其最低发射仅仅是来自于3MLCT/3LLCT的跃迁. 但是并不是所有的取代基为吸电子基团时都能有类似的π→π*跃迁性质. 对于化合物2, Cl是仅次于NO2的吸电子取代基, 但是由于缺少电子共振的贡献, 它的跃迁性质却与化合物3和4相同. 另外, 激发态几何相对于基态几何没有发生太大的变化, 这与实验上所观察到的较小斯托克斯频移现象一致.     

Facile synthesis and characterization of phosphorescent Pt(N(∧)C(∧)N)X complexes

In order to investigate the ground state and excited state properties of Pt(N(∧)C(∧)N)X, we have prepared a series of Pt complexes, where N(∧)C(∧)N aromatic chelates are derivatives of m-di(2-pyridinyl)benzene (dpb) and X are monoanionic and monodentate ancillary ligands including halide and phenoxide. Facile synthesis of platinum m-di(2-pyridinyl)benzene chloride and its derivatives, using controlled microwave heating, was reported. This method not only shortened the reaction time but also improved the reaction yield for most of the Pt complexes. Two Pt(N(∧)C(∧)N)X complexes have been structurally characterized by X-ray crystallography. The change of functional group does not affect the structure of the core Pt(N(∧)C(∧)N)Cl fragment. Both molecules pack as head-to-tail dimers, each molecule of the dimer related to the other by a center of inversion. The electrochemical studies of all Pt complexes demonstrate that the oxidation process occurs on the metal-phenyl fragment and the reduction process is associated with the electron accepting groups like pyridinyl groups and their derivatives. The maximum emission wavelength of the Pt(N(∧)C(∧)N)X complexes ranges between 471 and 610 nm, crossing the spectrum of visible light. Most of the Pt complexes are strongly luminescent (Φ = 0.32-0.63) and have short luminescence lifetimes (τ = 4-7 μs) at room temperature. The lowest excited state of the Pt(N(∧)C(∧)N)X complexes is identified as a dominant ligand-centered (3)π-π* state with some (1)MLCT/(3)MLCT character, which appears to have a larger (1)MLCT component than their bidentate and tridentate analogs. This results in a high radiative decay rate and high quantum yield for Pt(dpb)Cl and its analogs. However, the excited state properties of the Pt(N(∧)C(∧)N)X complexes are strongly dependent on the nature of the electron-accepting groups and substituents to the metal-phenyl fragment. A rational design will be needed to tune the emission energies of the Pt(N(∧)C(∧)N)X complexes over a wide range while maintaining their high luminescent efficiency.     

Tuning the Excited State of Photoactive Building Blocks for Metal‐Templated Self‐Assembly

The reaction of 2,2′:4,4′′:4′,4′′′‐quaterpyridyl (qtpy), with d⁶ ruthenium(II) (Ru^II), and rhenium(I) (Re^I) metal centers has been investigated. The pendant pyridyl groups on the products have also been methylated to produce a second series of complexes containing coordinated Meqtpy²⁺. The absorption spectra of the complexes are dominated by intraligand and charge‐transfer bands. The ruthenium(II) complexes display broad unstructured luminescence consistent with emission from a Ru(d)→diimine(π*) manifold in acetonitrile solutions. In aqueous solutions, their emissions are weaker and the lifetimes are shorter. This effect is particularly acute for complexes incorporating coordinated dipyridylpyrazine, dppz, ligands. Although the emission of the ruthenium(II) complexes containing Meqtpy²⁺ is generally shorter than their qtpy analogs, it is notable that solvent‐dependent effects are much less intense. The rhenium(I) complexes also display broad unstructured luminescence but, compared with the ruthenium(II) systems, they have a relatively short lifetime in acetonitrile. Electrochemical studies reveal that all of the Ru^II complexes display chemically reversible metal‐based oxidations. Re^I complexes only display irreversible metal‐based oxidations. In most cases, the reduction processes were not fully chemically reversible. The electrochemical and optical studies reveal that the nature of the lowest excited state of these complexes—particularly, the systems incorporating dppz—is highly dependent on the nature of the coordinated ligands. Calculations indicate that, although the excited state of most of the complexes is centered on the qtpy or Meqtpy²⁺ ligands, the excited state of the complexes containing dppz ligands is switched away from the dppz by qtpy methylation. A crystallographic study on one of the dicationic ruthenium(II) structures reveals that it forms an inclusion complex with benzene.