Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds

The photophysical properties of singlet and triplet metal-to-ligand charge transfer (MLCT) states of [Cu(I)(diimine)(2)](+), where diimine is 2,9-dimethyl-1,10-phenanthroline (dmphen), 2,9-dibutyl-1,10-phenanthroline (dbphen), or 6,6'-dimethyl-2,2'-bipyridine (dmbpy), were studied. On 400 nm laser excitation of [Cu(dmphen)(2)](+) in CH(2)Cl(2) solution, prompt (1)MLCT fluorescence with a quantum yield of (2.8 +/- 0.8) x 10(-5) was observed using a picosecond time-correlated single photon counting technique. The quantum yield was dependent on the excitation wavelength, suggesting that relaxation of the Franck-Condon state to the lowest (1)MLCT competes with rapid intersystem crossing (ISC). The fluorescence lifetime of the copper(I) compound was 13-16 ps, unexpectedly long despite a large spin-orbit coupling constant of 3d electrons in copper (829 cm(-1) ). Quantum chemical calculations using a density functional theory revealed that the structure of the lowest (1)MLCT in [Cu(dmphen)(2)](+) (1(1)B(1)) was flattened due to the Jahn-Teller effect in 3d(9) electronic configuration, and the dihedral angle between the two phenanthroline planes (dha) was about 75 degrees with the dha around 90 degrees in the ground state. Intramolecular reorganization energy for the radiative transition of 1(1)B(1) was calculated as 2.1 x 10(3) cm(-1), which is responsible for the large Stokes shift of the fluorescence observed (5.4 x 10(3) cm(-1)). To understand the sluggishness of the intersystem crossing (ISC) of (1)MLCT of the copper(I) compounds, the strength of the spin-orbit interaction between the lowest (1)MLCT (1(1)B(1)) and all (3)MLCT states was calculated. The ISC channels induced by strong spin-orbit interactions (ca. 300 cm(-1)) between the metal-centered HOMO and HOMO - 1 were shown to be energetically unfavorable in the copper(I) compounds because the flattening distortion caused large splitting (6.9 x 10(3) cm(-1)) between these orbitals. The possible ISC is therefore induced by weak spin-orbit interactions (ca. 30 cm(-1)) between ligand-centered molecular orbitals. Further quantum mechanical study on the spin-orbit interaction between the lowest (3)MLCT (1(3)A) and all (1)MLCT states indicated that the phosphorescence borrows intensity from 2(1)B(1). The radiative rate of the phosphorescence was also structure-sensitive. The flattening distortion reduced the transition dipole moment of 2(1)B(1) --> the ground state, and decreased the extent of mixing between 1(3)A and 2(1)B(1), thereby considerably reducing the phosphorescence radiative rate at the MLCT geometry compared to that at the ground state geometry. The theoretical calculation satisfactorily reproduced the radiative rate of ca. 10(3) s(-1) and accounted for the structure-sensitive phosphorescence intensities of copper(I) bis(diimine) compounds recently demonstrated by Felder et al. (Felder, D.; Nierengarten, J. F.; Barigelletti, F.; Ventura, B.; Armaroli, N. J. Am. Chem. Soc. 2001, 123, 6291).     

Theoretical study on photophysical properties of phenolpyridyl boron complexes

Organoboron complexes have potential application in organic light-emitting devices (OLEDs). Our group has synthesized four phenolpyridyl boron complexes (Inorg. Chem. 2006, 45, 2788), which can function as an electron transport materials (ETM), white and blue emitters, and exhibit high efficiency and stability. To reveal the relationship between the properties and structures of these functional materials, theoretical analysis of spectral properties and electronic structures of these complexes was systematically characterized with the B3LYP and 6-31G* basis set. The calculated absorption and emission spectra of these systems are in good agreement with the experimental ones. It is clear seen that these transitions are charge transferred along 2,6-bis(2-hydroxyphenyl)pyridyl boron moiety, and the contribution of boron atom in these compounds to the main transition orbitals is vanishingly small. The substitution of methyl and methoxyl for hydrogen does not change the absorption wavelengths and transition natures, but influences the radioactive efficiencies and electron transport properties, which are observed and discussed in detail. Furthermore, large red shifts of fluorescence are caused by replacing the hydrogen with CN or NO2 groups, which indicates that they are potential candidates as green-light-emitting materials. These results are favorable to further understanding the photophysical properties of this kind of complexes.     

Theoretical study on charge transport of quinacridone polymorphs

The charge carrier transporting ability in the polymorphism of quinacridone (QA) has been studied using density‐functional theory and Marcus charge transport theory. The theoretical results indicated quinacridone has good electron transport ability and electron mobilities of all the polymorphism are at 10^?2 magnitude. But its hole mobility, which varied with the different molecular packing, is at range of 10^?1–10^?3 magnitude. The difference of charge carrier mobilities among the polymorphism is originated from the different packing mode. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of isomerism/phase dependent charge transport properties in tris(8-hydroxyquinolinato)aluminum(III)

The charge carrier transporting ability in the polymorphism of tris(8-hydroxyquinolinato)aluminum(III) (Alq(3)) has been studied using density functional theory (DFT) and Marcus charge transport theory. α- and β-Alq(3) composed of mer-Alq(3) molecules have stronger electron-transporting property (n-type materials) compared with their hole-transporting ability. In contrast, γ- and δ-Alq(3) formed by fac-Alq(3) molecules possess stronger hole-transporting character than their electron-transporting ability. The detailed theoretical calculations indicate the reason lies in the differences of HOMO and LUMO distribution states of the two kinds of isomers, and the different molecular packing modes of charge-transporting pathways for different phases.     

Photogeneration of charge carriers and their transport properties in poly[bis(p-n-butylphenyl)silane

The photocarrier generation mechanism and mobility in poly[bis(p-n-butylphenyl)silane] (PBPS) thin films doped with a variety of electron acceptors are studied by time-resolved microwave conductivity (TRMC) measurements. It was found that fullerene is a suitable electron acceptor for PBPS as it provides the highest product of photocarrier generation yield phi and mobility Sigmamu under excitation at 532 and 355 nm. The observed high phiSigmamu value of 4.5 x 10(-3) cm(2)/(V s) under excitation at 193 nm (6.39 eV) can be attributed to the direct ionization of PBPS molecules. The photoinduced electron transfer between C(60) and PBPS was investigated in a solution sample by laser flash photolysis under excitation at 532 nm. On the basis of the extinction coefficient of PBPS(*+), transient absorption of PBPS(*+) provides a maximum value of phi of 0.83% for the electron-transfer reaction from PBPS to (3)C(60). On the basis of this value of phi, the intrinsic intrachain mobility of holes on the PBPS backbone is estimated to be higher than 1.7 x 10(-2) cm(2)/(V s), suggesting the presence of a high conducting path along the Si backbone of PBPS.     

Variable-temperature and solvent NMR study of bis(μ2-methanethiolato)-bis(dinitrosyliron) and bis(μ2-methaneselenolato)-bis(dinitrosyliron)

The ¹H NMR spectrum of Fe₂(SMe)₂(NO)₄ has been measured in a total of 22 solvents, and the activation barrier ΔG^≠ for the C_2h?C_2v isomerisation in nine of these solvents. In aromatic solvents, the solvent-induced shifts are consistent with the formation of charge-transfer complexes, either 1:1 or 1:n; in non-aromatic, non-halogenated solvents of high dipolarity/polarizability the solvent-induced shifts follow the variation of the solvatochromic parameter, π*. The behaviour of Fe₂(SeMe)₂(NO)₄ in a limited range of solvents is similar. The activation barrier ΔG^≠ in Fe₂(SMe)₂(NO)₄ is ca 78 kJ mol^?1 in the majority of solvents, but that for Fe₂(SeMe)₂(NO)₄ is significantly higher.     

Synthesis and properties of polyimides derived from 1,6-bis(4-aminophenoxy)naphthalene and aromatic tetracarboxylic dianhydrides

1,6-Bis(4-aminophenoxy)naphthalene ( I ) was used as a monomer with various aromatic tetracarboxylic dianhydrides to synthesize polyimides via a conventional two-stage procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by thermal cyclodehydration to polyimides. The diamine ( I ) was prepared through the nucleophilic displacement of 1,6-dihydroxynaphthal-ene with p-chloronitrobenzene in the presence of K₂CO₃, followed by catalytic reduction. Depending on the dianhydrides used, the poly(amic acid)s obtained had inherent viscosities of 0.73–2.31 dL/g. All the poly(amic acid)s could be solution cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimide films had a tensile modulus range of 1.53–1.84 GPa, a tensile strength range of 95–126 MPa, and an elongation range at break of 9–16%. The polyimide derived from 4,4′-sulfonyldiphthalic anhydride (SDPA) had a better solubility than the other polyimides. These polyimides had glass transition temperatures between 248–286°C (DSC). Thermogravimetric analyses established that these polymers were fairly stable up to 500°C, and the 10% weight loss temperatures were recorded in the range of 549–595°C in nitrogen and 539–590°C in air atmosphere. © 1995 John Wiley & Sons, Inc.     

Theoretical characterization of charge transport in chromia (alpha-Cr2O3)

Transport of conduction electrons and holes through the lattice of alpha-Cr2O3 (chromia) is modeled as a valence alternation of chromium cations using ab initio electronic structure calculations and electron-transfer theory. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e., the reorganization energy and the electronic coupling matrix element that enter Marcus' theory. The calculation of the electronic coupling followed the generalized Mulliken-Hush approach using the complete active space self-consistent-field (CASSCF) method and the quasidiabatic method. Our findings indicate that hole mobility is more than three orders of magnitude larger than electron mobility in both (001) and [001] lattice directions. The difference arises mainly from the larger internal reorganization energy calculated for electron-transport relative to hole-transport processes while electronic couplings have similar magnitudes. The much larger hole mobility versus electron mobility in alpha-Cr2O3 is in contrast to similar hole and electron mobilities in hematite alpha-Fe2O3 previously calculated. Our calculations also indicate that the electronic coupling for all charge-transfer processes of interest is smaller than for the corresponding processes in hematite. This variation is attributed to the weaker interaction between the metal 3d states and the O(2p) states in chromia than in hematite, leading to a smaller overlap between the charge-transfer donor and acceptor wave functions and smaller superexchange coupling in chromia. Nevertheless, the weaker coupling in chromia is still sufficiently large to suggest that charge-transport processes in chromia are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron-spin coupling within the Cr-Cr donor-acceptor pair, while the reorganization energy is essentially independent of the electron-spin coupling.     

Theoretical study on photophysical properties of 2,1,3-benzothiadiazole-based star-shaped molecules

Star-shaped molecules with tailoring functional groups in the core and the arms have great potential application in organic light-emitting devices, because it can be designed to realize low band gap, broad absorption, and excellent solubility for low-cost solution process. To gain an insight into the structure?Cproperty relationships, a set of four-arm star-shaped molecules with 2,1,3-benzothiadiazole as the core, different ??-conjugated groups as the arm, and triphenylamine or 2-(pyridin-2-yl) pyridine as the end-group were designed. In this study, a systematic investigation into them was carried out using the density functional theory and time-dependent density functional theory methods. The calculated ionization potentials, electron affinities, and reorganization energies (??) show that the properties of the ??-conjugated bridge and the end-group significantly affect the carrier injection and transport characteristics of these molecules, especially for S-BTDP and S-EBTD. Among these molecules, S-BTDP exhibits better electron injection ability due to the introduction of 2-(pyridin-2-yl) pyridine as the end-group. However, S-EBTD, with ethylene as ??-conjugated bridge, has excellent hole injection and carrier transport behaviors. We also calculated the singlet-to-triplet exciton-formation cross-section ratio (??_S/??_T), the exciton-formation fractions (??_S), and the absorption and emission spectra of these molecules. We calculated that ??_S/??_T ranges from 1.78 to 2.76 and that ??_S is ca. 0.37?C0.48. These molecules have two absorption bands in the range of 340?C410?nm and 500?C613?nm, respectively. The calculated emission spectra range from 619 to 706?nm. It can be deduced that the studied 2,1,3-benzothiadiazole-based star-shaped molecules can serve as efficient red light-emitting electroluminescent materials.     

Theoretical study of substituent effect on the charge mobility of 2,5-bis(trialkylsilylethynyl)-1,1,3,4-tetraphenylsiloles

The theoretical calculation of the charge mobility of 2,5-bis(trialkylsilylethynyl)-1,1,3,4-tetraphenylsiloles is presented. B3LYP/6-31* calculations demonstrated that these silole molecules possessed large coupling matrix elements and reorganization energies for electron and hole transfers and high electron mobilities. The bulkiness of the trialkyl substituents influenced the charge mobility of the silole molecules, with the smaller trimethyl group imparting higher charge mobility than triethyl and triisopropyl substituents.     

两种四噻吩并萘分子晶体电荷传输性质的理论研究

采用密度泛函理论(DFT)方法结合不相干的电荷跳跃模型和随机Monte Carlo模拟,研究了2种四噻吩并萘晶体(AT1和AT2)的分子结构、电子性质及电荷载流子传输参数,并预测了这2种晶体室温下空穴和电子迁移率的各向异性.结果表明标题化合物具有近似平面的刚性骨架结构,电荷传输过程中分子的结构弛豫相当小.基于绝热势能面法计算的AT1和AT2分子空穴/电子传输内重组能分别为9.300×10~(-2)/1.100×10~(-1)eV和1.020×10~(-1)/1.290×10~(-1) eV,外重组能分别为1.835×10~(-2)/1.711×10~(-2) eV和1.857×10~(-2)/1.747×10~(-2) eV.利用Monte Carlo随机模拟方法预测的2种分子晶体室温(300K)下空穴/电子迁移率平均值分别为4.976×10~(-3)/2.766×10~(-2) cm~2 V~(-1)s~(-1)和3.857×10~(-3)/1.478×10~(-2)cm~2 V~(-1)s~(-1).此外,迁移率的角度依赖性研究表明2种载流子在AT1和AT2晶体aob平面传输时表现出显著的各向异性,其最大值均沿着电荷传输积分最大的方向,为制备高性能场效应晶体管器件提供了参考.     

Theoretical and experimental study on metal(II) halide complexes of 1,3-bis(4-pyridyl)propane

We report the results of detailed experimental and theoretical studies on the molecular structure and vibrational spectra of metal(II) halide complexes of 1,3-bis(4-pyridyl)propane [M(N₂C₁₃H₁₄)X₂, where M represents Zn or Hg, and X represents Cl, Br, or I]. The FT–infrared spectra (FT-IR) and FT-Raman spectra of the metal complexes of the 1,3-bis(4-pyridyl)propane molecule in the powder form were recorded between the 400–4000 and 5–3500 cm^?1 regions, respectively. The molecular geometry and vibrational frequencies of the metal complexes of 1,3-bis(4-pyridyl)propane in the ground state were calculated using density functional theory (B3LYP functional) with LANL2DZ and SDD as basis sets. The total energy distributions (TED) among the symmetry coordinates of the normal modes were computed for the low-energy structure of the molecules. Complete vibrational assignments based on the calculated TED values are given.     

Synthesis,structures and photophysical properties of phosphorus-containing silver 3,5-bis(trifluoromethyl)pyrazolates

Reaction of a trinuclear silver pyrazolate {[3,5-(CF₃)₂Pz]Ag}₃ complex with tricyclohexylphosphine at different reagent ratios leads to the formation of heteroleptic dinuclear or tetranuclear complexes. According to the single crystal X-ray analysis of the dinuclear complex, hexane molecules are incorporated into the cavities formed as the result of supramolecular packing. Coordination of a phosphine ligand makes dinuclear silver pyrazolate to exhibit blue emission at room temperature.     

Synthesis and properties of aromatic polyamides derived from 1,6-bis(4-aminophenoxy)naphthalene and aromatic dicarboxylic acids

A new bis(phenoxy)naphthalene-containing diamine, 1,6-bis(4-aminophenoxy)naphthalene, was synthesized in two steps from the condensation of 1,6-dihydroxynaphthalene with p-chloronitrobenzene in the presence of potassium carbonate, giving 1,6-bis(4-nitrophenoxv)naphthalene, followed by hydrazine hydrate/Pd—C reduction. A series of polyamides were synthesized by the direct polycondensation of the diamine with various aromatic dicarboxylic acids in the N-methyl-2-pyrrolidone (NMP) solution containing dissolved metal salts such as CaCl₂ or LiBr using triphenyl phosphite and pyridine as condensing agents. The polymers were obtained in quantitative yield with inherent viscosities of 0.78–3.72 dL/g. Most of the polymers were soluble in aprotic solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), NMP, and they could be solution-cast into transparent, flexible and tough films. The casting films had tensile strength of 102–175 MPa, elongation at break of 8–42%, and tensile modulus of 2.4–3.8 GPa. The polymers derived from rigid dicarboxylic acids such as terephthalic acid and 4,4′-biphenyldicarboxylic acid exhibited some crystalline characteristics. The glass transition temperatures of the polyamides were in the range of 238–337°C, and their 10% weight loss temperatures were above 487°C in nitrogen and above 438°C in air. © 1995 John Wiley & Sons, Inc.     

The mass spectral rearrangements of 1,6-bis(arylsulfenyl)-2,4-hexadiynes and 1,6-bis(arylsulfonyl)-2,4-hexadiynes

The mass spectral. behavior of 1,6-bis(arylsulfenyl)-2,4-hexadiynes and 1,6-bis(arylsulfonyl)-2,4-hexadiynes were examined. The sulfenyl derivatives extruded the hexadiynyl moiety with the formation of Ar? S? S? Ar fragments. The sulfonyl derivatives, on the other hand, showed no extrusion of the hexadiyne fragment but an expulsion of SO₂ and even two SO₂ units.     

Theoretical study on photophysical properties of novel bis(BF2)‐2,2′‐bidipyrrins dyes: Effect of variation in monomer structure

In this work, monomeric molecules (BODIPY) 4,4‐difluoro‐1,2,3,5,7‐pentamethyl‐6‐ethyl‐4‐bora‐3a,4a‐diaza‐s‐indacene ( 1 ), 4,4‐difluoro‐1,7‐dimethyl‐2,3,6‐terethyl‐8‐(4‐tolyl)‐4‐bora‐3a,4a‐diaza‐s‐indacene ( Ph1 ), dimeric monomers (bisBODIPY) 2 , Ph2 , and their packing systems were taken as calculation models to investigate the relationship between monomeric structures and spectral properties of packing systems. Their spectra and carrier transport properties were systemically investigated by density functional theory and time‐dependent DFT methods. The results reveal that dimeric monomers bisBODIPY 2 and Ph2 show significantly bathochromic shift and exhibit a clear exciton splitting in the absorption spectrum compared with those of 1 and Ph1 . Monomeric and dimeric molecules have different monomer conformations (nearly flat and corniform, respectively) and thus diverse packing styles. The intermolecular aggregation affects the excitation energy and oscillator strength of monomers 1 and Ph1 more than those of the corniform monomers 2 and Ph2 . The unique corniform structure of molecules 2 and Ph2 can greatly reduce self‐quenching effect induced by the formation of excimers. This means that suitable modification of molecular arrangement is an effective way to reduce self‐quenching. From the calculation results for molecules Ph1 and 1 , the aryl group at the 8‐position of BODIPY core can hardly affect the optical properties. According to our calculations, BODIPY 1 is a better hole transporter than electron transporter with the internal reorganization energy for hole (λ⁺) even lower than that of 4,4′‐bis(phenyl‐mtolylamino)biphenyl (TPD), a well‐known hole‐transporting material. Molecules Ph1 , BisBODIPYs 2 , and Ph2 are promising candidate to be excellent ambipolar materials for electroluminescent devices, owing to their quite small and nearly identical reorganization energies for both carriers. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Theoretical study on second-order nonlinear optical properties of unsymmetric bis (phenylethynyl) benzene series derivatives

On the basis of ZINDO methods, according to the sum-overstates (SOS) expression, the program for the calculation of the second-order nonlinear optical susceptibilities βijk and βμ of molecules was devised, and the structures and nonlinear optical properties of unsymmetric bis (phenylethynyl) benzene series derivatives were studied. The influence of the molecular conjugated chain lengths, the donor and the acceptor on βμ was examined.