Individual but connected synthetic routes for the preparation of the all-E-configured 2,5-dipropoxy-substituted oligo(l,4-phenyleneethenylene)~ 1 a-g were developed An increasing number of conjugated stilbene units from n = 1 to n = 11 led to a convergent bathochromic shift (Ah = h, -h, = 127 nm) in the UV/Vis absorption An exponential function for the convergence of the absorption energies (wavelengths) in conlugated systems is proposed By a simple extrapolation of this function the effective chain length may be determined Among the conjugated polymers poly( 1,4-phenyleneetheny1ene)s [polyb-phenylenevinylene)s, PPV] are receiving increasing attention as conductive materials (upon doping), photoconductors, materials for light-emitting diodes and nonlinear optics ['].A crucial question for all these applications is: How does the length of the conjugated chain influence the properties? Polymers exist as polydisperse mixtures and therefore contain components with suitable or less suitable properties.Another disadvantage is the occurrence of structural defects. PPVs, mostly synthesized by the precursor method[';'], contain for example saturated carbon centers in their chain, which interrupt the conjugation. Incomplete elimination processes are responsible for these defects. A further defect in the PPV chain can originate from the formation of (aconfigured double bonds, which induce a high torsion of the chain and impair therefore the conjugation. All these drawbacks can be avoided by the preparation of specific oligoniers, but one should not forget in the discussion polymers versus oligomers, that polymer systems mostly exhibit better mechanical properties, especially the capability of generating films.Some time ago we elaborated a novel procedure for the preparation of 2-alkoxy-, 3-alkoxy-, and 2,5-dialkoxy-substituted oligo-and poly( 1,4-phenyleneethenylene)~[~"]. The alkoxy side chains enhance the solubility and lower the HOMO-LUMO gap and the band gap, respectively'']. On the other hand, conjugation is influenced by the torsion in the chain which reflects the contribution of different conformations based on the substitution pattern[? Concerning the photoconductivity the best results were obtained for 2,s-dipropoxy-substituted PPVS[~.~I. However, again the question of the optimum length of the main chain remained still unanswered. Therefore, we decided to synthesize and investigate the monodisperse 2,5-dipropoxy-substituted oligo( 1,4-phenyIeneethenylene)s 1 a-g. SynthesesThe final step in all synthetic sequences of la-g was the formation of one or two CC double bonds by applying the
A novel family of functionalized polystyrenes that are susceptible to base-catalyzed β-elimination is reported. A study of the thermal behaviors of poly[(((((2-cyano-1,1-dimethylethyl)oxy)carbonyl)oxy)styrene], poly[(((2-cyanoethoxy)carbonyl)oxy)styrene], and poly[((((2-methylsulfonyl)ethoxy)carbonyl)oxy)styrene] confirms that they undergo facile and quantitative elimination of their side chain groups in a process that is susceptible to base catalysis. Imaging of these polymer systems was accomplished using the novel ,4,4‘-[bis[[(2-nitrobenzyl)oxy]carbonyl]trimethylene]dipiperidine as an amine photogenerator. Copolymerization of ((((2-cyano-1,1-dimethylethyl)oxy)carbonyl)oxy)styrene and ((t-butoxycarbonyl)oxy)styrene followed by selective deprotection of the t-BOC protecting groups with acid enabled the synthesis of a base-sensitive copolymer containing free phenol units with enhanced thin-film properties.
The 2-styryl-1,4-benzoquinones 7a,b, generated by the oxidation of the corresponding hydroquinones 6a,b, dimerize at room temperature in a Diels−Alder reaction. The strictly chemo-, regio-and stereoselective process can be rational-
2-Styryl-1,4-benzoquinone (1) and compounds 2 and 3 containing 1 as a substructure all proved to be highly reactive towards thermal or photochemical [4π + 2π] cyclodimerization reactions. Chemo-, regio-and stereoselective processes lead to dimers (compounds 1−10), which can undergo secondary reactions consisting of the addition of nucleophiles combined with a twofold keto-enol tautomerism (10 Ǟ 12). An alternative process is dehydrogenation/oxidation followed by an intramolecular [4π + 2π] cycloaddition (10 Ǟ 11).
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