Cyclodepolymerization as a method for the synthesis of macrocyclic oligomers

Macrocyclic oligomers (MCOs) are important as starting materials for Entropically-driven Ring-opening Polymerizations (ED-ROPs). This article reviews the preparation of MCOs by the cyclodepolymerization (CDP) of condensation polymers. Many MCOs have been prepared successfully this way and in numerous cases individual macrocycles have been isolated. This approach can provide one-step syntheses of many macrocycles. The combination of CDP plus ED-ROP is an attractive potential method for recycling (‘Ring-chain Recycling’) many condensation polymers.     

Synthesis,Liquid‐Crystalline Properties,and Photo‐optical Studies of Photoresponsive Oligomeric Mesogens as Dopants in a Chiral Glassy Liquid Crystal

We have prepared photoresponsive oligomers that have molecular weights of ca. 4500, 8000, and 16 000 g mol^–1 via the free‐radical polymerization of 4‐[4‐alkylphenylazo]phenoxyalkyl acrylates. All of the oligomers possess bilayer smectic A (SmA) and smectic B (SmB) phases. Increasing the concentration of these oligomeric dopants in a glass‐forming cholesteric liquid crystal causes a dramatic red‐shift in the reflection wavelength. The pitch shifts are very dependent on the alkyl chain lengths and molecular weights of the dopants. The oligomer that contains octyl chains and an octyl spacer, and that has a molecular weight of 4500 g mol^–1 exhibits the largest shift in the reflection wavelength. UV exposure has been used to control the cholesteric reflection pitch of the oligomer‐cholesteric glassy liquid‐crystal mixture over the entire visible region of the electromagnetic spectrum and vitrifies the samples by rapid cooling from their cholesteric temperatures to 0 °C. Extremely stable, even at 70 °C, erasable, full‐color images have been created using this host–guest mixture.     

New kinds of phenylethynyl-terminated polyimide oligomers with low viscosity and good hydrolytic stability

In continuing studies to develop low melt viscosity phenylethynyl end-capped imide oligomers for aerospace applications, new kinds of all-aromatic phenylethynyl-terminated imide oligomers were prepared by the reaction of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) or biphenylenetetracarboxylic dianhydride (s-BPDA) with 2,5-bis(4-aminophenoxy)-biphenyl (p-TPEQ) and 4-phenylethynylphthalic anhydride (PEPA) or 4-(1-phenylethynyl)1,8-naphthalic anhydride (PENA). The oligomers bearing pendant phenyl groups exhibit much lower melt viscosities at low temperatures, and thus provide wide processing window. The thermal curing process of the oligomers was investigated with DSC. The tensile and thermal properties of the cured films were evaluated. Oligomers derived from PENA cured at lower temperatures and the corresponding cured polymers show better hydrolytic stability than those of PEPA. Results showed that the utilization of diamine monomer (p-TPEQ) can improve the processability and solubility of phenylethynyl-terminated imide oligomers without sacrificing their thermo-oxidative stability.     

2,7‐Carbazolenevinylene‐Based Oligomer Thin‐Film Transistors: High Mobility Through Structural Ordering

We have fabricated organic field‐effect transistors based on thin films of 2,7‐carbazole oligomeric semiconductors 1,4‐bis(vinylene‐(N‐hexyl‐2‐carbazole))phenylene (CPC), 1,4‐bis(vinylene‐(N′‐methyl‐7′‐hexyl‐2′‐carbazole))benzene (RCPCR), N‐hexyl‐2,7‐bis(vinylene‐(N‐hexyl‐2‐carbazole))carbazole (CCC), and N‐methyl‐2,7‐bis(vinylene‐(7‐hexyl‐N‐methyl‐2‐carbazole))carbazole (RCCCR). The organic semiconductors are deposited by thermal evaporation on bare and chemically modified silicon dioxide surfaces (SiO₂/Si) held at different temperatures varying from 25 to 200 °C during deposition. The resulting thin films have been characterized using UV‐vis and Fourier‐transform infrared spectroscopies, scanning electron microscopy, and X‐ray diffraction, and the observed top‐contact transistor performances have been correlated with thin‐film properties. We found that these new π‐conjugated oligomers can form highly ordered structures and reach high hole mobilities. Devices using CPC as the active semiconductor have exhibited mobilities as high as 0.3 cm² V^–1 s^–1 with on/off current ratios of up to 10⁷. These features make CPC and 2,7‐carbazolenevinylene‐based oligomers attractive candidates for device applications.     

Responses of Human Cells to PAH-Induced DNA Damage

Benzo[ a ]pyrene (B[ a ]P) and dibenzo[ a,l ]pyrene (DB[ a,l ]P) induce cytochrome P450 (CYP) CYP1A1 and CYP1B1, which metabolize these polycyclic aromatic hydrocarbons (PAHs) into DNA-binding species. In order to detail roles of CYP1A1 and CYP1B1 in activation of DB[ a,l ]P to the diol epoxide, we here report the inhibition of CYP1A1 in human MCF-7 cells with phosphorodiamidate morpholino antisense oligomers (morpholinos). PAH-DNA adduct formation was also determined after treatment with morpholinos and B[ a ]P or DB[ a,l ]P. p53 is involved in DNA repair, cell cycle arrest, and apoptosis. Cells with normal p53 protein arrest in the G1 phase of the cell cycle on exposure to DNA-damaging agents (presumably allowing the cell sufficient time to repair damaged DNA prior to replication). Previous studies in human MCF-7 cells indicate that cells with PAH-DNA adducts escape cell cycle arrest and accumulate in the S phase. In the present study the effect of PAH-DNA adducts on the cell cycle were observed in human diploid fibroblasts (HDF). We found that treatment of HDF with the diol epoxide of DB[ a,l ]P causes cell cycle arrest in G 1 . An increase in DNA adduct formation with increase in concentration of dibenzo[ a,l ]pyrene diol epoxide {( m )- anti -DB[ a,l ]PDE} was also observed.     

Synthesis and properties of solution-processible oligomers for the use of organic light-emitting diodes (OLEDs)

Two oligomers with X-shaped repeating units bearing anthracene and fluorene units were synthesized in a facile procedure, and exhibited high photoluminescence efficiencies, thermal stabilities and good solubility. Their ease of processing enabled spin coating with an electron-transporting bitriazine layer to afford organic light-emitting diodes which displayed a light blue emission with the maximum luminance of 3650 cd/m² and the current efficiency of 0.69 cd/A at an operation voltage of 10 V.     

Synthese von Oligo(p‐phenylen‐m‐pyridindiyl)en

Oligomers ( 7 , 9 , 11 , and 13a ‐ c ), which consist of an alternate sequence of 1,4‐linked benzene rings and 2,4‐linked pyridine rings, were prepared from the corresponding oligochalcones. Each enone segment reacts with phenacylpyridinium bromide ( 3 ) and ammonium acetate ( 4 ) to yield a pyridine building block. Propoxy sidechains attached on the benzene rings of the chalcones reduce to some extent the yield of the cyclization reactions (40–68%) but enhance the solubility of the oligomers. Cross conjugation leads to a moderate bathochromic shift of the absorption with increasing number of repeating units.