1.2- diethynylbenzene

Beside the polymerization routes of 1,3-cyclohexadiene derivatives repetitive Diels-Alder polyadditions were widely used to prepare arylated PPPs. Stille et al. developed a set of suitable monomers (1,4-diethynylbenzene and 1,4-phenyl-ene-bis(triphenylcyclopentadienone) derivatives) to generate phenylated PPPs (e.g. 17) with molecular weights of 20,000-100,000 [31]. Unfortunately, the repetitive polyadditon does not proceed regioselectively polymers containing para-as well as mefa-phenylene units within the main chain skeleton are formed. 

Tetra-dehydrobromination of the compound in benzene with ethanolic potassium hydroxide for the commercial production of 1,4-diethynylbenzene is highly exothermic and needs careful control to avoid hazard. 

Figure 4. The various mechanisms for structural "shrink-wrapping" in bilayer GS inclusion compounds can be gleaned from these illustrative examples, here viewed down the channel direction, (a) quasihexagonal G2IH 2(CH3CN), (b) quasihexagonal G2V-1,4-diethynylbenzene, (c) shifted...

In THF at 20°C, dendritic monomers 3a-3c show absorption bands at 335 and 278 nm, due to the focal 1,4-diethynylbenzene unit and the dendritic wedges, respectively. On the other hand, dendritic macromolecular rods 2a-2c display a strong absorption band in the visible region (400-460 nm), characteristic of an extended electronic conjugation in the backbone. Upon excitation of the conjugated backbone at 425 nm in THF (abs425 nm = 0.01) at 20°C, 2a-2c show a strong blue fluorescence at 454 nm, where the quantum yield ( FL) has been evaluated to be virtually 100%. Of much interest is the fact that the fl>FL value of 2c stays at nearly 100%, even when the solution is concentrated until the... 

Water-soluble PPEs have been made by the suitable choice of ionic and highly hydrophilic side chains. These PPEs will play a role in bio-type sensing applications (vide infra). A clever example is Schanze s synthesis of a sulfonato-substituted PPE [40, 41]. The NaOH-promoted reaction of [1, 2]oxathiolane-2,2-dioxide with 2,5-diiodohydroquinone gives a bis-sulfonate that can be coupled (Pd-catalyzed) to 1,4-diethynylbenzene to form a water-soluble PPE (Scheme 4) Table 6, entry 1). In a similar approach, Schanze et al. [42] made a... 

Metathesis of W2(OBu )e with one C=C triple bond of substituted 1,4-diethynylbenzenes has given carbyne complexes which can be converted into trans-WCl(=CC6H4C=CH)(dmpe)2. Functionalization via the W—Cl and =CH groups affords metalladiynes such as frans-W C=C(tol) (=CC6H4C=CSiPr 3)... 

A very bulky group, such as trimethylsilyl, tends to occupy the 4-position. Addition of phenyl azide to phenyltrimethylsilylacetylene gives almost exclusively the 4-trimethylsilyltriazole. This can be useful because of the ease of removal of trimethylsilyl substituents. Additions to diacetylenes and addition of p-diazidobenzene to 1,4-diethynylbenzene are also claimed to be regiospecific. 

A new family of Pt(II) polyyne polymers functionalized with substituted 1,4-diethynylbenzene derivatives 8—14 were synthesized and optically characterized by absorption and PL studies.20 In regard to the emission properties, it is interesting to see that the relative intensity of triplet emission increases strongly with the electronegative fluorine content in such system. 

Oxidative polymerization of 1,4-diethynylbenzene into highly conjugated poly(phenylene butadiynylene) within the channels of surface-functionalized mesoporous silica and alumina materials. J. Am. Chem. Soc. 124 9040-9041. 

Analogously, aromatic high molecular weight poly(pyridone)s have been obtained using terminal and internal aromatic diynes, e.g. 1,4-diethynylbenzene [98] and l,4-bis(phenylethynyl)benzene [99] respectively, for 1 1 cycloaddition copolymerisation with isocyanates. 

Scheme 13. The synthesis of rod-like oligomers and polymers of 1,4-diethynylbenzene (45).

As depicted in Scheme 4, the treatment of 1,4-diethynylbenzene with 2eq. of diphenylbromoborane (selective haloboration) and the subsequent reaction with leq. of tolylene-2,4-diisocyanate (phenylboration polymerization) gives the corresponding alternating copolymers. 

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