Hybridization of Long Pyridine‐Dicarboxamide Oligomers into Multi‐Turn Double Helices: Slow Strand Association and Dissociation,Solvent Dependence,and Solid State Structures

Oligoamides of 2,6‐diaminopyridine and 2,6‐pyridinedicarboxylic acid comprised of 5, 7, 9, 11, or 13 units and bearing 4‐isobutoxychains on all pyridine rings and tert‐butyl‐carbamate terminal groups have been synthesized stepwise, along with an 11 mer having benzyl‐carbamate terminal groups. The crystal structure of all five Boc‐terminated compounds has been obtained and shows a highly regular and conserved double helical hybridization motif of up to 3 complete turns for the 13 mer. Four pyridine units span one helical turn and define a helix pitch of ca 7 Å. Solution studies in CDCl₃ demonstrated that the Boc‐terminated oligomers strongly hybridize in this solvent, and that K_dim values increase with oligomer length. The K_dim values are 31000 and 7×10⁵ L mol^?1 for the 7 mer and the 9 mer, respectively, and are too high to be measured by NMR for the 11 mer and the 13 mer. Hybridization and dissociation kinetics at 2 mM proceed at decreasing rates upon increasing oligomer length. The rate was faster than minutes for the 7 mer, of the order of hours for the 9 mer, and days for the 11 mer and 13 mer. The same trend was observed in [D₅]pyridine but with considerably lower K_dim values and faster kinetics. The benzylcarbamate 11 mer was also found to hybridize into a double helix but with reduced K_dim values and faster kinetics compared to its Boc‐terminated analogue. Combined with previous studies, the results presented here frame a global understanding of the hybridization of these pyridinecarboxamide oligomers and provide useful guidelines for the design of other artificial double helices.     

Synthesis,Structure, and Nonlinear Optical Properties of Cross‐Conjugated Perphenylated iso‐Polydiacetylenes

Monodisperse, cross‐conjugated perphenylated iso‐polydiacetylene (iso‐PDA) oligomers, ranging from monomer 15 to pentadecamer 25 , have been synthesized by using a palladium‐catalyzed cross‐coupling protocol. Structural characteristics elucidated by X‐ray crystallographic analysis demonstrate a non‐planar backbone conformation for the oligomers due to the steric interactions between alkylidene phenyl groups. The electronic absorption spectra of the oligomers show a slight red‐shift of the maximum absorption wavelength as the chain length increases from dimer 17 b to pentadecamer 25 , a trend that has saturated by the stage of nonamer 22 . Fluorescence spectroscopy confirms that the pendent phenyl groups present on the oligomer framework enhance emission, and the relative emission intensity consistently increases as a function of chain length n. The molecular third‐order nonlinearities, γ, for this oligomer series have been measured via differential optical Kerr effect (DOKE) detection and show a superlinear increase as a function of the oligomer chain length n. Molecular modeling and spectroscopic studies suggest that iso‐PDA oligomers (n>7) adopt a coiled, helical conformation in solution.     

Unusual Aggregation of Nanosized Six‐Arm Star Oligofluorenes

A series of monodisperse six‐arm benzene‐cored star oligofluorenes are prepared by a divergent/convergent strategy, starting from the repetitive divergent synthesis of symmetrical ethynyl‐bridged oligofluorenes to the convergent Co‐catalyzed alkyne cyclotrimerization. The structures of these six‐arm molecules are fully characterized. The diameter of the largest molecule SF3 reaches ca. 3 nm. These highly substituted star‐shaped oligomers exhibit extremely high fluorescent quantum yields in solution and unexpected red‐shifted and broadened emission with fine structure in the film as a result of the formation of stable aggregates.

     

Scalability of Coarse‐Grained Potentials Generated from Iterative Boltzmann Inversion for Polymers: Case Study on Polycarbonates

Using systematic coarse‐grained (CG) techniques such as iterative Boltzmann inversion (IBI) is an efficient means to simulate high molecular weight polymer melts within reasonable computational time. One drawback of such an approach is however the need to carry out extensive atomistic simulations in order to extrapolate the necessary distributions to derive the inter and intrabead force field parameters. Here it is shown that it is possible to use atomistic simulations of relative short oligomers to develop the CG model for high molecular weight polymers. In particular for the specific case of polycarbonates, it is found that the structural properties (end‐to‐end distance, radius of gyration and their distributions) are similar irrespective of whether the CG potentials are derived from 5‐mer or 10‐mer melt systems. Dynamical properties of the CG systems are smoother and faster than the atomistic ones. Scaling factor, derived by overlapping the CG mean square displacement curves (obtained from different CG IBI potentials) over the atomistic ones, also scales the autocorrelation functions. A prediction of the dynamical scaling factor in the case of the unavailability of atomistic simulations is also discussed. The dynamical properties of the CG melts are modeled reasonably well by all the CG potentials derived from atomistic simulations of short oligomers.

     

Zigzag molecules from pyrene-modified carbazole oligomers: synthesis, characterization, and application in OLEDs

A series of monodisperse, pyrene-modified oligocarbazoles were synthesized and fully characterized. Carbazoles were linked by ethynylene through the 3- and 6-positions, forming a zigzag molecular backbone and stable, size-independent absorption, and emission were observed from these oligomers in solutions because their conjugation length was confined. Oligomers with pyrene exhibited much higher fluorescence quantum yields than those of oligomers without it. Different positions of pyrene in the oligocarbazole main chain resulted in a remarkable change in absorption and emission spectra. Moreover, devices with four different architectures (types 1-4) based on these oligomers were fabricated and investigated. Pyrene-modified carbazole oligomers exhibited bifunctional properties (light-emitting and hole-transport). Moreover, these devices showed moderate performances; for example,the device based on Cz3PyCz3 presented an external quantum efficiency of 0.69% and a maximum brightness of 1782 cd/m2 at 13.5 V, which indicated these oligomers were promising optoelectric materials.     

Solution‐Processed,Undoped, Deep‐Blue Organic Light‐Emitting Diodes Based on Starburst Oligofluorenes with a Planar Triphenylamine Core

A series of starburst oligomers (T1–T3) that contained a fully diarylmethene‐bridged triphenylamine core and oligofluorene arms were designed and synthesized through Suzuki cross‐coupling reactions. Their thermal, photophysical, and electrochemical properties were also investigated. These materials showed high glass transition, in the range of 123–129 °C, and good film‐forming abilities. They displayed deep‐blue emission both in solution and as thin films. Solution‐processed devices based on these oligomers exhibited highly efficient deep‐blue electroluminescence and the device performances were significantly enhanced with the extension of the oligofluorene arms. The double‐layered device that contained T3 as an emitter showed a maximum current efficiency of 3.83 cd A^?1 and a maximum external quantum efficiency of 4.19 % with CIE coordinates of (0.16, 0.09), which are among the highest values for undoped deep‐blue OLEDs that are based on solution‐processable starburst oligomers.     

Synthesis and Fluorescent Properties of Tetra‐Biphenyl N‐Substituted Phthalimides

A series of tetra(biphenyl‐4‐yl)phthalimide (TBPPI ) derivatives with different N‐substituents (n‐butyl, phenyl, p‐methyl phenyl, and p‐acetyl phenyl moieties for compounds 7 – 10 , respectively) were prepared to examine their fluorescent behavior under various conditions. The chemical structure of compound 7 has been successfully confirmed by single crystal X‐ray diffraction analysis. The photoluminescence (PL ) spectra in different ratios of CH ₂Cl ₂/EtOH mixture solutions revealed that compounds 7 and 8 exhibited both aggregation‐induced emission (AIE ) and aggregation‐caused quenching (ACQ ) behaviors, while compounds 9 and 10 displayed AIE and aggregation‐induced emission enhancement (AIEE ) properties, respectively.     

The Synthesis,Photophysical Characterization,and X‐Ray Structure Analysis of Two Polymorphs of 4,4′‐Diacetylstilbene

A palladium(II) acetate‐catalyzed synthesis of 1 that utilizes the novel triazene 1‐{4‐[(E)‐morpholin‐4‐yldiazenyl]phenyl}ethanone as a synthon is described. The room temperature absorption spectra of 1 in various solvents exhibited a π→π* transition in the range of 330–350 nm. Compound 1 was observed to be luminescent, with room‐temperature solution and solid‐state emission spectra that exhibited maxima in the range 400–500 nm. All room‐temperature absorption and emission spectra exhibited some degree of vibrational structure. The emission spectrum of 1 at 77 K in propanenitrile glass was broad and featureless with a maximum at 447 nm. Compound 1 crystallized as a yellow and colorless polymorph. X‐Ray structure analyses of both of these polymorphs and 1‐{4‐[(E)‐morpholin‐4‐yldiazenyl]phenyl}ethanone are presented.     

A Novel Route to 1‐Substituted 3‐(Dialkylamino)‐9‐oxo‐9H‐indeno[2,1‐c]pyridine‐4‐carbonitriles

Heptalenecarbaldehydes 1 / 1′ as well as aromatic aldehydes react with 3‐(dicyanomethylidene)‐indan‐1‐one in boiling EtOH and in the presence of secondary amines to yield 3‐(dialkylamino)‐1,2‐dihydro‐9‐oxo‐9H‐indeno[2,1‐c]pyridine‐4‐carbonitriles (Schemes 2 and 4, and Fig. 1). The 1,2‐dihydro forms can be dehydrogenated easily with KMnO₄ in acetone at 0° (Scheme 3) or chloranil (=2,3,5,6‐tetrachlorocyclohexa‐2,5‐diene‐1,4‐dione) in a ‘one‐pot’ reaction in dioxane at ambient temperature (Table 1). The structures of the indeno[2,1‐c]pyridine‐4‐carbonitriles 5′ and 6a have been verified by X‐ray crystal‐structure analyses (Fig. 2 and 4). The inherent merocyanine system of the dihydro forms results in a broad absorption band in the range of 515–530 nm in their UV/VIS spectra (Table 2 and Fig. 3). The dehydrogenated compounds 5, 5′ , and 7a – 7f exhibit their longest‐wavelength absorption maximum at ca. 380 nm (Table 2). In contrast to 5 and 5′, 7a – 7f in solution exhibit a blue‐green fluorescence with emission bands at around 460 and 480 nm (Table 4 and Fig. 5).     

Synthesis and light‐emitting properties of carbazole‐based copolymers bearing cyano‐substituted arylenevinylene chromophore

Two arylenevinylene compounds bearing the cyano group at α‐position ( 6 ) and β‐position ( 9 ) from the dialkoxylphenylene unit were synthesized, in which the molecular termini were functionalized with 3‐bromocarbazole. The Suzuki coupling copolymerization of these compounds with 1,4‐bis[(3′‐bromocarbazole‐9′‐yl)methylene]‐2,5‐didecyloxybenzene and 9,9‐dihexylfluorene‐2,7‐bis(boronic acid) was carried out to obtain copolymers ( cp67 and cp97 ) containing the cyano‐substituted arylenevinylene fluorophore of 7 mol %. Model compounds ( 6 ′ and 9 ′) corresponding to the arylenevinylene fluorophore were also prepared. The UV spectra of copolymers resembled that of homopolymer hp with no arylenevinylene segment in both CHCl₃ solution and thin film. The emission maxima of copolymers in CHCl₃ (394 nm) agreed with that of homopolymer indicating that the emission bands originated from the carbazole‐fluorene‐carbazole segment. The emission maximum wavelength of copolymer cp67 in thin film (477 nm) indicated fluorescence from the cyano‐substituted arylenevinylene fluorophore because of the occurrence of fluorescence resonance electron transfer. In contrast, copolymer cp97 showed fluorescence at 528 nm to suggest the formation of a new emissive species such as a charge‐transfer complex (exciplex). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 91–98, 2010     

Eu^3+和Eu^3+在LnBaB~9O~16是的紫外和真空卜外发光性质

研究了Tb^3+和En^3+在LnBaB~9O~16(Lu=La,Gd,Y,Lu)中的卜外和真空紫外光谱性质。X射线粉未衍射数据脂标化结果表明,LnBaB~9O~16(Lu=La,Gd,Y,Lu)系列化合物属于三方晶系。Eu^3+的荧光光谱结果表明,LnBaB~9O~16和GdBaB~9O~16中稀土离子占据非是心对称的格位,Eu^3+在其中的特征发射5D0→7F2电偶极跃迁为主;而在YBaB9O16和LuBaB9O16中稀土离子占据中心对称性的格位,Eu3^+在其中的特征发射以5D0→7F1磁偶极跃迁为主.     

Synthesis and properties of a series of well-defined and polydisperse benzo[1,2-b:4,3-b']dithiophene oligomers

Monodisperse and polydisperse oligomers of benzo[1,2-b:4,3-b']dithiophene (BDT) (1-14), including three types of oligomers with different spacers combining BDT units (direct linkage, vinylene spacers, and ethynylene spacers), were synthesized, and their thermal, optical, and electrochemical properties were investigated. The oligomers were synthesized using Suzuki, Stille, Wittig, and Sonogashira coupling reactions. All of the monodisperse oligomers showed high melting points and 5% weight loss temperatures (T(d) > 400 degrees C). The fluorescence maxima of all oligomers were red-shifted, and the emission colors varied from blue to yellow as the chain lengths-and thus the conjugation lengths-increased. The vinylene-bridged oligomers emitted at longer wavelengths than the direct-linked and ethynylene-bridged oligomers. UV-vis absorption spectra in toluene solution indicated an effective conjugation length of about six BDT units for polydisperse oligomer 5. Cyclic voltammetry measurement indicated that tetramer 3 had high electrochemical stability. Although tetramer 3 and vinylene-bridged tetramer 8 exhibited reversible oxidation waves, ethynylene-bridged tetramer 13 showed an irreversible oxidation process. Each type of monodisperse oligomer exhibited higher HOMO levels with increasing chain length.     

Synthesis, Characterization and Weak Intramolecular Interactions of Porphyrins Bearing Nucleobases

5,10, 15-Triphenyl-20-{2- [α- (adenine-9 ) acetylamino]} phenyl porphyrin ( 1 ), 5,10, 15-triphenyl-20-{2-[α-(cytosine-1)acetylamino]} phenyl porphyrin (2), 5, 10, 15-triphenyl-20-{4-[α-(cytosine-1)ethoxy]} phenyl porphyrin (3) and their zinc complexes Zn-1, Zn-2 and Zn-3 have been prepared and characterized by ^1H NMR spectra, elemental analyses, electronic absorption spectra and mass spectra (FAB). Intramolecular π-π interactions and intramolecular metal-~ interaction for 1, 2, Zn-1,and Zn-2 have been investigated by several methods. ^1H NMR studies demonstrate that the porphyrin π-system in 1 and 2 is parallel to the adenine and the cytosine aromatic ring, respectively. The electronic absorption spectral properties of free porphyrin derivatives and their zinc complexes have been compared with those of H2TPP and ZnTPP. The results show that the UV-vis spectra of 1 and 2 are the same as that of H2TPP,whereas the spectra of their zinc complexes show 7 nm red shifts of the Soret bands compared to that of ZnTPP. The emission spectra of Zn-1 and Zn-2 are independent of excitation wavelength. From combination of the evidence of absorption and emission spectra it is suggested the existence of intramolecular metal-π interaction in Zn-1 and Zn-2. The results of conformational analysis agreed quite nicely with that of experiments, thus it was further to validate the experimental conclusions.     

High quantum yield photoluminescence of new polyamides containing oligo‐PPV amino derivatives and related oligomers

The synthesis and the chemical physical characterization of new photoluminescent (PL) chromophores and polymers are reported. Chromophores (oligo‐PPV symmetric derivatives ending with amino groups) are strong blue emitters with a PL quantum yield of ～70% in dioxane solution. They have been used to prepare polyamides by reaction with aliphatic acyl dichlorides in which emitting and non emitting units are alternated. PL properties of the synthesized polyamides have been evaluated in solution and reveal a strong blue emission (PL quantum yield ～60%), To increase the solubility of these systems, oligomers have been purposely prepared and then characterized. They show a peculiar white emission when excited in DMF solution; to get insight into this interesting behavior, asymmetric monoacetylated chromophores have been prepared as model compounds for the chromophoric end groups of the polyamide chains. The emission spectra of these compounds reveal a broad excimeric yellow emission which is responsible, along with the blue emission of the inner chromophoric units, of the overall white emission of the oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2677–2689, 2009     

Bioguided Isolation and Antiproliferative Activity of Constituents from Smilax korthalsii A.D.C. Leaves

Ethyl acetate extract of Smilax korthalsii A.D.C. leaves exhibited antiproliferative activity on leukaemia carcinoma K562, hepatic liver cancer cells WRL and colorectal carcinoma with IC₅₀ of 125.20, 46.10 and 160.00 μM respectively. Isolation of the bioactive ethyl acetate extract of Smilax korthalsii A.D.C. leaves gave eight compounds; 3β‐hydroxyspirost‐5‐ene (diosgenin), 1 , β‐sitosterol, 2 , lup‐5,11,20‐trien‐23‐ol, 3 , uneicos‐9‐enoic acid, 4 , ethylheptadecan‐17‐oic‐9‐enoate, 5 , cis‐octadec‐9‐enoic acid, 6 , hexadec9‐enoic acid, 7 and 11‐methyltridec‐12‐en‐1‐ol, 8 . The isolated compounds were tested against four human cancer cell lines: leukaemia carcinoma, K‐562; hepatic liver cancer cells, WRL; colorectal carcinoma, COLO; and breast carcinoma, MCF‐7 using the MTT assay. Diosgenin 1 exhibited significant antiproliferative activity against all four cell lines (IC₅₀; K562=6.25, WRL=14.34, COLO=38.00, MCF‐7=12.40 μM), while compounds 3, 6 and 7 inhibited the growth of K‐562 at 20, 50 and 100 μM concentrations with IC₅₀ of 90.20, 75.92 and 50.72 μM respectively. Other isolated compounds also showed cytotoxic properties against K‐562, WRL and COLO, but showed low inhibition of MCF‐7.     

Oligonucleotides Functionalized by Fluorescein and Rhodamine Dyes: Michael Addition of Methyl Acrylate to 2′‐Deoxypseudouridine

The 2′‐deoxypseudouridine ( 5 ) was functionalized at N(1) with methyl acrylate by Michael addition. The resulting methyl 2′‐deoxypseudouridine‐1‐propanoate ( 6 ) was converted to the phosphoramidite 8 and to the amino‐functionalized derivative 9 , which was transformed into the fluorescein‐labeled phosphoramidites 14 and 16 . Fluorescent oligonucleotides were synthesized either from these building blocks or by post‐synthetic modification of oligomers containing 2′‐deoxypseudouridine subunits. The stability of oligonucleotide duplexes was determined from the melting profiles, measured by UV‐ or VIS‐light absorbance, as well as from the fluorescence emission spectra. While small spacer residues did not affect the thermal stability of the 2′‐deoxypseudouridine‐containing duplexes, large dye residues led to destabilization.     

Concise Synthesis of Well‐Defined Linear and Branched Oligothiophenes with Nickel‐Catalyzed Regiocontrolled Cross‐Coupling of 3‐Substituted Thiophenes by Catalytically Generated Magnesium Amide

The synthesis of linear and branched oligothiophenes of well‐defined structures is performed with regioselective deprotonation of 3‐substituted thiophenes and nickel‐catalyzed cross‐coupling of the thus formed metalated species with a bromothiophene. The reaction of 3‐hexylthiophene with EtMgCl and 2,2,6,6‐tetramethylpiperidine (TMP‐H, 10 mol %) induces the metalation selectively at the 5‐position by use of the catalytically generated hindered magnesium amide (TMPMgCl) and the subsequent reaction of a 2‐halo‐3‐hexylthiophene (bromide or chloride) in the presence of a nickel catalyst affords a head‐to‐tail (HT)‐type dimer. By repeating the same sequence, the linear oligothiophene up to a 4‐mer is synthesized in good yield. The reaction of 3‐hexylthiophene with 2,3‐dibromothiophene also takes place to afford a branched oligothiophene 3‐mer in quantitative yield. The obtained 3‐mer is also metalated at the sterically less‐hindered position in a regioselective manner furnishing a 7‐mer in >99 % yield after a further coupling reaction with 2,3‐dibromothiophene. These dendrimers react with several multifunctionalized organic electrophiles, leading to a variety of branched oligothiophenes.     

Synthesis and mesomorphic properties of new chiral banana‐shaped liquid crystals with chiral 3‐(alkoxy)propoxy terminal groups

New chiral banana‐shaped liquid crystals with chiral 3‐(alkoxy)propoxy terminal groups (Pn‐O‐PIMB5*‐4O, n = 7, 8, 9 and 10) were synthesized and their mesomorphic properties and phase structures investigated by means of electro‐optic measurements, polarizing optical microscopy, differential scanning calorimetry, and second harmonic generation measurements. Most of these chiral bent‐core mesogens (n = 7–9) showed the antiferroelectric B2 phase, whereas P10‐O‐PIMB5*‐4O exhibited the B7 phase. Comparing with the previously reported homologue Pn‐O‐PIMB(n‐2)*, we conclude that the terminal chain structure, particularly the position of chiral centres, plays an important role in the emergence of particular phase structures.     

Electronic Structure Calculations for Hole‐Transporting Triphenylamine Derivatives in Polymer Light‐Emitting Diodes

Hole‐transporting polymers based on polyethene‐triphenylamine derivatives are investigated with respect to their UV/Vis spectra. Two substituents, N‐phenyl‐1‐naphthylamine and carbazole, are examined as their respective polymer light‐emitting diodes (PLEDs) show very different luminous efficiencies. In order to identify the origin of these phenomena electronic structure calculations based on TD‐DFT were performed using monomer models of the hole‐transporting polymers. In experiment these hole‐transporting polymers show very specific differences in their absorption and emission (fluorescence and phosphorescence) spectra. The analysis of the simulated absorption and emission spectra, the MOs as well as the ground and excited state geometries give explanations for the different optical performances of the corresponding PLEDs.

     

Molecularly defined (L)‐lactic acid oligomers and polymers: Synthesis and characterization

The synthesis of (L )‐lactide oligomers from dimer to 64mer via an exponential growth strategy is described. By careful selection of orthogonal protective groups, the synthesis were conducted using a t‐butyldimethylsilyl (TBDMS) ether as the protective group of the hydroxyl group and benzyl (Bn) ester as the protective group of the carboxylic acid group. The yields of both the deprotection steps and coupling reactions using 1,3‐dicyclohexylcarbodiimide or 1‐[3‐(dimethylamino)propyl]‐3‐ethylcarbodiimide hydrochloride were high (70–100%) and the absence of a requirement for conducting the majority of reactions under an inert atmosphere permitted a robust and efficient synthetic strategy to be developed. This allowed monodisperse dimer, tetramer, octamer, 16mer, 32mer, and 64mer materials to be prepared in gram quantities and fully characterized using mass spectrometry and size exclusion chromatography. Evaluation of the thermal and physical properties using thermogravimetric analysis, differential scanning calorimetry, and small angle X‐ray scattering demonstrated a close correlation between the molecular structure of the well‐defined Poly(lactide) oligomers and their physical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5977–5990, 2008