π-Conjugated Unit-Dependent Optical Properties of Linear Conjugated Oligomers

The optical properties of three linear conjugated oligomers （F-P, F-P-F, and P-F-P-F-P）, where phenothiazine （P） and fluorene （F） groups arrange alternately, are investigated. With the enhancement of the π-conjugated system, their absorption and emission bands both gradually red shift, and their two-photon properties are also improved. Meanwhile, their fluorescence dynamic traces are analyzed with continuous rate distribution model, exhibiting that their decay rates gradually accelerate and the rate distribution width become narrower. The quantum chemical calculation offers their molecular structures and transition mechanism, showing that the enhancement of π-conjugated system should be responsible for tile improvement of two-photon properties.     

Theoretical Study on Optical Properties of Oligo°uorenes

We present theoretical investigations on structure-property correlations in fluorenone (FLO) and benzothiadiazole (BT) substituted oligofluorenes (OFLs) derived mainly from the chain morphology, thermal vibration and conjugated extent. Both the vertical absorptions and the vibrationally-resolved absorption and fluorescence spectra have been calculated by the com-bination of ab initio and time-dependent density functional theory. By properly taking into account of the anharmonic torsion potentials in the OFLs, we have reasonably reproduced the experimentally observed spectroscopic features. Both FLO and BT on-chain chemical defects acting as charge-trapping sites for singlet excitations, are responsible for long wave absorption and emission species, and thus alter the blue light-emitting properties of OFLs. As temperature decreases, the electronic spectral lineshapes of FLO-substituted oligomers become more structured. The lineshapes of BT-substituted oligomers are always smooth and featureless because of less low collective modes resonance. A more gentle excited poten-tial energy surface of BT-mixed molecules can enhance electronic delocalization and achievebigger red shifts.     

One-Pot Synthesis of 3-to 15-Mer π-Conjugated Discrete Oligomers with Widely Tunable Optical Properties

A series of all-donor type alternating (D1-D2) monodisperse oligomers based on cyclopentadithiophene (CPDT) and 1,4-difluorobenzene (DFB) with gradually increas...     

Substituents Effect on the Optical Properties of Benzonitrile and Oligobenzonitriles

During the past decades, the organic systems with good electronic and optical property,such as oligomer and polymers, have been attracted much attention because of theiroptical nonlinearity, fast response, relatively low cost, ease of fabrication and integrationinto devices. Generally to say, the common oligomers or polymers that we usually studyare all of carbon-carbon or heteroaromatic conjugated system. In previous work, thesynthesis of new linear -(C=N).- conjugated systems, polynitriles h…     

Optical Properties of Fullerenated Poly(epoxy propyl carbazole)

Sincethedevelopmentofmethodslformassproductionoffullerenes,therehasbeengTeatinterestinit-Manyresearchgroups'havepaidgreatattentiontothefiJllerene-dopedpolymersinceWang'discoveredinl992thatfullerene-dopedPVKhasanapparentlyincreasingphotoconductivity.WehavereportedthechendcalattachmentofCcocagestothecarbazolegroupsonpoly(epoxypropylcarbazole)(PEPC)chainsbyFriedel-Craftstypereaction'.Here,theopticalpropertiesoffullerenatedPEPCwereinvestigated,whichwillshowitsgoodphotoconductivepropeFtiesbe…     

Synthesis, Characterization and Properties of Novel Star-Shaped π-Conjugated Oligomers with Triphenylamine Core

Four new star‐shaped π‐conjugated oligomers ( TPA‐CZ3 , TPA‐TPA3 , TPA‐PTZ3 and TPA‐BT3 ) with triphenylamine as a core and different electron‐donating ability groups, carbazole, triphenylamine, phenothiazine and bithiophene, as peripheral units have been designed and synthesized via the Heck reaction. These oligomers show good solubility in common organic solvents. Their photophysical, electrochemical, electronic structure and charge transfer properties between these star‐shaped π‐conjugated oligomers and N,N′‐bis(1‐ethylpropyl)‐3,4:9,10‐perylene bis(tetracarboxyl diimide) (EP‐PDI) have been investigated by UV‐vis absorption spectra, photoluminescence (PL) spectra, cyclic voltammetry (CV) measurement, theoretical calculations and fluorescence quenching. The results show that the absorptions and fluorescences of TPA‐CZ3 , TPA‐TPA3 and TPA‐PTZ3 are red shifted with the electron‐donating ability of the peripheral unit increasing from carbazole to triphenylamine and phenothiazine. In addition, although the bithiophene group has a weaker electron‐donating ability than carbazole, triphenylamine and phenothiazine, the absorption and fluorescence of TPA‐BT3 have a red shift than those of TPA‐CZ3 , TPA‐TPA3 and TPA‐PTZ3 because TPA‐BT3 has a longer conjugation length than TPA‐CZ3 , TPA‐TPA3 and TPA‐PTZ3 . The triphenylamine core and the peripheral units can constitute a large conjugated structure. The fluorescence quenching properties indicate that efficient charge transfer can happen between the star‐shaped oligomers and EP‐PDI.     

Electrochemistry of platinum(II) porphyrins: effect of substituents and π-extension on redox potentials and site of electron transfer

Fourteen platinum(II) porphyrins with different π-conjugated macrocycles and different electron-donating or electron-withdrawing substituents were investigated as to their electrochemical and spectroscopic properties in nonaqueous media. Eight compounds have the formula (Ar(4)P)Pt(II), where Ar(4)P = the dianion of a tetraarylporphyrin, while six have π-extented macrocycles with four β,β'-fused benzo or naphtho groups and are represented as (TBP)Pt(II) and (TNP)Pt(II) where TBP and TNP are the dianions of tetrabenzoporphyrin and tetranaphthoporphyrin, respectively. Each Pt(II) porphyrin undergoes two reversible one-electron reductions and one to three reversible one-electron oxidations in nonaqueous media. These reactions were characterized by cyclic voltammetry, UV-visible thin-layer spectroelectrochemistry and in some cases by ESR spectroscopy. The two reductions invariably occur at the conjugated π-ring system to yield relatively stable Pt(II) π-anion radicals and dianions. The first oxidation leads to a stable π-cation radical for each investigated porphyrin; but in the case of tetraarylporphyrins containing electron-withdrawing substituents, the product of the second oxidation may undergo an internal electron transfer to give a Pt(IV) porphyrin with an unoxidized macrocycle. The effects of macrocycle structure on UV-visible spectra, oxidation/reduction potentials, and site of electron transfer are discussed.     

Nonlinear Optical Properties of D-π-A-π-D Type Oligomers with Different Conjugation Length

The conjugation length-dependent nonlinear optical properties of fluorenone-based linear conjugated oligomers have been investigated by experimental and theoretical methods. In-frared spectra and the steady-state absorption spectra show that the increase of conjugated unit could enhance the stretching vibration peaks of C=C and lead to a red-shift of the absorption peaks. Meanwhile, the two-photon fluorescence (TPF) intensity is gradually en-hanced with the increase of excitation energy, and the TPF effciency is obviously higher after the introduction of fluorene-ethylene units. The sum-over-states approach was used to model the two-photon absorption (TPA) cross-sections of oligomers, and the theoretical values agree well with the experimental data obtained from the femtosecond open-aperture z-scan technique. The results exhibit that the extension of conjugated system indeed plays a role in the improvement of TPA behavior of oligomers.     

Development of Functionalized Cyclotriveratrylene Analogues: Introduction of Withdrawing and π-Conjugated Groups

Cyclotriveratrylene analogues (CTVs) are supramolecular bowl-shaped molecules known for their ability to complex organic and organometallic guests, to form liquid crystals, polymers, or nanostructures. In this Article, we report the synthesis of new cyclotriveratrylene analogues with fluorescence properties in which various electron-withdrawing or π-extended conjugated groups are appended to the wide rim ortho to the methoxy-donating groups. Synthetically, these functionalized CTVs cannot be obtained as CTVs with electron-rich functions by the typical method (i.e., the trimerization of the corresponding benzyl alcohol) but are prepared from a common key intermediate, the C(3)-triiodocyclotriveratrylene (CTV-I(3)), in good yields. Despite the synthetic difficulties encountered due to the presence of three reactive centers, we have demonstrated the possibility of performing Sonogashira coupling and Huisgen cycloaddition reactions directly to the CTV core for the first time. CTVs with π-extended conjugated groups reveal interesting fluorescence profiles. More broadly, this study utilizes CTV-I(3) to introduce novel functionalities into CTVs to keep exploring their potential applications.     

Chemistry of Anthracene–Acetylene Oligomers XX: Synthesis,Structures, and Self-Association of Anthracene–Anthraquinone Cyclic Compounds with Ethynylene Linkers

We have synthesized anthracene–acetylene oligomers, which contained one 10-substituted anthracene unit and one anthraquinone unit, by cyclization with Sonogashira coupling. X-ray analysis revealed an almost-planar framework and significant out-of-plane deformation around the inner carbonyl moiety because of steric hindrance. These compounds underwent self-association in solution and their association constants for monomer–dimer exchange were determined by variable-concentration ¹H NMR measurements in CDCl₃: 8 mol⁻¹ L (10-substituent: isopropyl), <5 mol⁻¹ L (methoxy), and 19 mol⁻¹ L (octyloxy). These results were discussed on the basis of spectroscopic and molecular-orbital analysis. A linear molecular assembly of the octyloxy compound at a liquid/graphite interface was observed by STM measurements.     

Switchable Nonlinear Optical Properties of η(5)-Monocyclopentadienylmetal Complexes: A DFT Approach

Density functional theory (DFT) calculations have been carried out to investigate the switching of the second-order nonlinear optical (NLO) properties of η(5)-monocyclopentadienyliron(II) and ruthenium(II) model complexes presenting 5-(3-(thiophen-2-yl)benzo[c]thiophen-1-yl)thiophene-2-carbonitrile as a ligand. The switching properties were induced by redox means. Both oxidation and reduction stimulus have been considered, and calculations have been performed both for the complexes and for the free benzo[c]thiophene derivative ligand in order to elucidate the role played by the organometallic fragment on the second-order NLO properties of these complexes. B3LYP, CAM-B3LYP, and M06 functionals were used for our calculations. The results show some important structural changes upon oxidation/reduction that are accompanied by significant differences on the corresponding second-order NLO properties. TD-DFT calculations show that these differences on the second-order NLO response upon oxidation/reduction are due to a change in the charge transfer pattern, in which the organometallic iron and ruthenium moieties play an important role. The calculated static hyperpolarizabilities were found to be strongly functional dependent. CAM-B3LYP, however, seems to predict more reliable structural and optical data as well as hyperpolarizabilities when compared to experimental data. The use of this functional predicts that the studied complexes can be viewed as acting as redox second-order NLO switches, in particular using oxidation stimulus. The β(tot) value of one-electron oxidized species is at least ～8.3 times (for Ru complex) and ～5.5 times (for Fe complex) as large as that of its nonoxidized counterparts.     

Benchmarking of Density Functionals for the Description of Optical Properties of Newly Synthesized π-Conjugated TADF Blue Emitters

Computational modeling of the optical characteristics of organic molecules with potential for thermally activated delayed fluorescence (TADF) may assist markedly the development of more efficient emitting materials for organic light-emitting diodes. Recent theoretical studies in this area employ mostly methods from density functional theory (DFT). In order to obtain accurate predictions within this approach, the choice of a proper functional is crucial. In the current study, we focus on testing the performance of a set of DFT functionals for estimation of the excitation and emission energy and the excited singlet-triplet energy gap of three newly synthesized compounds with capacity for TADF. The emitters are designed specifically to enable charge transfer by π-electron conjugation, at the same time possessing high-energy excited triplet states. The functionals chosen for testing are from various groups ranging from gradient-corrected through global hybrids to range-separated ones. The results show that the monitored optical properties are especially sensitive to how the long-range part of the exchange energy is treated within the functional. The accurate functional should also be able to provide well balanced distribution of the π-electrons among the molecular fragments. Global hybrids with moderate (less than 0.4) share of exact exchange (B3LYP, PBE0) and the meta-GGA HSE06 are outlined as the best performing methods for the systems under study. They can predict all important optical parameters correctly, both qualitatively and quantitatively.     

Living Crystallization-Driven Self-Assembly of Oligo(p-phenylene vinylene)-Containing Block Copolymers: Impact of Branched Structure of Alkyl Side Chain of π-Conjugated Segment

The structure of side chains of π-conjugated segments is a critical factor determining living crystallization-driven self-assembly(CDSA),a versatile platform to generate fiber-like nanostructures with precise length and composition. Herein, we design and synthesize three block copolymers(BCPs) containing same corona-forming poly(N-isopropyl acrylamide)(PNIPAM) segment, but different core-forming π-conjugated oligo(p-phenylene vinylene)(OPV) with linear pentyl(l-OPV), racemic 2-methyl butyl(r-OPV...     

Copolymerization of ω-Unsaturated Oligo(Methyl Methacrylate): New Macromonomers

Abstract

The free-radical copolymerization of ω-unsaturated oligo(methyl methacrylate) (1) with each of ethyl acrylate, styrene, methyl methacrylate, acrylonitrile, and vinyl acetate have been investigated. Incorporation of (1) into the polymer was observed in all cases although the molecular weights of the copolymers were substantially lower than those of the homopolymers obtained in the absence of (1) but under otherwise identical conditions. These experiments, together with a product study of the reactions of (1) with cyanoisopropyl radicals, have shown that the addition of free radicals to the double bond of (1) occurs readily. The sterically hindered radical so formed, however, undergoes facile β-scission, resulting in the termination of chains (chain transfer) in competition with chain propagation. The implications of these findings to the usefulness of (1) in the synthesis of graft copolymers and their relevance to the chemistry of free-radical polymerizations when methyl methacrylate is employed as a monomer or comonomer are discussed.     

Growth and Optical Properties of Sr_6YbSc(BO_3)_6 Crystal

1INTRODUCTION As is well known,the Yb3 ion has some advan-tages in comparison with Nd3 as laser active ion,for it has only two manifolds,i.e.,the ground2F7/2state and the excited2F5/2state.There is no excited state absorption reducing effective laser cross-section,no concentration quenching,no up-conversion,and three or four times longer emission lifetime than Nd3 ion.Yb3 ion exhibits a strong and broad ab-sorption band at ca.970nm and can be easily pumped with InGaAs diode lasers.The …     

Effect of intraligand π-delocalization on the photophysical properties of two new Ru(II) complexes

Two new Ru(II) complexes, [Ru(bpy)₂(1-COO-iqu)]⁺ (2; bpy = 2,2′-bipyridine, 1-COO-iqu^? = isoquinoline-1-carboxylate) and [Ru(bpy)₂(3-COO-iqu)]⁺ (3; 3-COO-iqu^? = isoquinoline-3-carboxylate), were prepared and their crystal structures solved. The ground and excited state properties of 2 and 3 were characterized and compared to those of [Ru(bpy)₃]²⁺ (1). The presence of the oxygen atom in the Ru(II) coordination sphere makes 2 and 3 easier to oxidize than 1. The Ru → bpy MLCT absorption and emission of 2 and 3 are red-shifted relative to that of 1 in CH₂Cl₂, and the E₀₀ energies were estimated to be 1.89 eV and 1.95 eV from the low temperature emission of 2 and 3, resulting in excited state oxidation potentials of ?1.03 V and ?1.10 V vs SCE, respectively. In addition to the short-lived emissive ³MLCT state, a long-lived species is observed in the transient absorption of 3 in DMSO (τ = 49 μs) and pyridine (τ = 44 μs), assigned to a solvent-coordinated complex. This intermediate is not observed for 3 in non-polar solvents or for 2. The absence of the solvent coordinated intermediate in 2 is explained by the stronger Ru–O bond afforded by the lower conjugation in that extends onto the carboxylic acid in the 1-COO-iquo^?ligand, compared to that in the 3-COO-iqu^?ligand in 3. Transient absorption experiments also show that the ³MLCT excited state of 3 is able to reduce methyl viologen.     

Correlating Molar Mass, π-Conjugation,and Optical Properties of Narrowly Distributed Anionic Polythiophenes in Aqueous Solutions

Polythiophene-based conjugated polyelectrolytes (CPE) are attracting increasing attention as sensor or interface materials in chemistry and biology. While cationic polythiophenes are better understood, limited structural information is available on their anionic counterparts. Limited access to well-defined polymers has made the study of structure-property relationships difficult and clear correlations have remained elusive. By combining controlled Kumada catalyst transfer polymerization with a polymer-analog substitution, regioregular and narrowly distributed poly(6-(thiophen-3-yl)hexane-1-sulfonate)s (PTHS) with tailored chain length are prepared. Analysis of their aqueous solution structures by small-angle neutron scattering (SANS) revealed a cylindrical conformation for all polymers tested, with a length close to the contour length of the polymer chains, while the estimated radii remain too small (<1.5 nm) for extensive π-stacking of the chains. The latter is particularly interesting as the longest polymer exhibits a concentration-independent structured absorption typical of crystalline polythiophenes. Increasing the ionic strength of the solution diminishes these features as the Coulomb repulsion between the charged repeat units is shielded, allowing the polymer to adopt a more coiled conformation. The extended π-conjugation, therefore, appears to be a key parameter for these unique optical features, which are not present in the corresponding cationic polythiophenes.     

Linear Multiselenium Interactions in Dicationic Oligomers of 1,5-(Diselena)canes: Behavior of Semc σ(mcc-nee) (6≤mc≤16) Elucidated with QTAIM Dual Functional Analysis

The intrinsic dynamic and static nature m_c center-n_e electron interactions of the σ-type σ(m_cc-n_ee) were elucidated for the Se-Se interactions in dicationic oligomers of Se(CH₂CH₂CH₂)₂Se ( 1 (Se, Se)) [ n ²⁺ (Se, Se): n=1–8], especially for m_c≥6, where n ²⁺ (Se, Se: n=1–8) are abbreviated by n ²⁺ (n=1–8), respectively. QTAIM dual functional analysis (QTAIM-DFA) was applied to the interactions. Perturbed structures generated using coordinates derived from the compliance constants (C_ii) were employed for QTAIM-DFA. Each Se-*-Se in 1 ²⁺ and 2 ²⁺ has the nature of CT-TBP (trigonal bipyramidal adduct formation through CT) and Cov-w (weak covalent), respectively, which supply the starting points of the investigations. The asterisk emphasizes the existence of a bond critical point on the interaction. All Se-*-Se in 3 ²⁺ are classified by the regular closed shell (r-CS) interactions and characterized as CT-MC (molecular complex formation through CT), which are denoted as r-CS/CT-MC, except for the central interaction, of which nature is r-CS/CT-TBP. Most interactions in 4 ²⁺– 8 ²⁺ are r-CS/t-HB_wc (typical-HB with covalency) but some are pure-CS/t-HB_nc (t-HB with no covalency). The linear Se_2n²⁺ interactions in 2 ²⁺– 8 ²⁺ seem close to those without any limitations, since the nature of Se-*-Se inside and outside of (CH₂CH₂CH₂)₂ are very similar with each other. The linear Se_2n²⁺ interactions in 3 ²⁺– 8 ²⁺ are shown to be analyzed as σ(m_cc-n_ee: 6≤m_c≤16), not by the accumulated σ(3c–4e).     

Synthesis, Structure, Magnetism and Electrochemical Properties of Linear Pentanuclear Complex: Ni5(μ-dmpzda)4(NCS)2

吡啶修饰的线性五核金属化合物[Ni5(μ-dmpzda)4(NCS)2][ dmpzda-H2=N,N’-Di(4-methyl pyrydin-2-yl)pyrazine-2,6-diamine]被合成并表征,其电化学和磁性被报告。 化合物含有接近180º的 Ni-Ni-Ni角,末端含有两个轴配体的Ni5 线性链。这个五核线性金属链被四个顺式的dmpzda2-配体螺旋包裹。化合物中存在两种类型的Ni-Ni键长：末端连接有轴配体的Ni-Ni键长被配体影响,其键长为2.3821 Å;内部的Ni-Ni距离比较短,为2.2959 Å。两末端的Ni(II)离子由于连接轴配体构成四方锥形(NiN4NCS)并存在较长的Ni-N 键长（2.103 Å),这个键长符合高自旋Ni(II)构型。内部的三个Ni-N 距离为1.886-1.906 Å,这样构成正方形平面(NiN4)并呈低自旋的顺磁构型。化合物显示了同[Ni5(μ-tpda)4(NCS)2]类似的磁性,即在化合物中两末端Ni(II)仍存在反铁磁性的作用。