Synthesis and Characterization of Conjugated Polyazines and Polyazomethines Containing the Thienylene Moiety and Flexible Hydrocarbon Side Chains Silvia Destri,* ,† Mariacecilia Pasini, † Corrado Pelizzi, ‡ William Porzio, † Giovanni Predieri,* ,‡ and Carlo Vignali § Istituto di Chimica delle Macromolecole del CNR, via E.Bassini 15, I-20133 Milano, Italy, Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita ` di Parma, Viale delle Scienze, I-43100 Parma, Italy, and Centro Interdipartimentale di Misure “Giuseppe Casnati”, Universita ` di Parma, Viale delle Scienze, I-43100 Parma, Italy Received July 28, 1998; Revised Manuscript Received October 16, 1998 ABSTRACT: Condensation reactions of mono- and didodecyl-substituted-2,5-diformylthiophene with hydrazine, p-diaminobenzene, 2,7-diaminofluorene, and 1,5-diaminonaphatalene give the corresponding polyazines (PAZs) and polyazomethines (PAMs), which have been characterized by thermal, structural, and optical analyses. The former polymers begin to decompose at 300 °C, while the latter polymers are stable up to 360 °C. All disubstituted polymers and the regioregular monosubstituted polyazines show nematic character. Disubstituted polymers display a larger conjugation with respect to monosubstituted ones. This effect has been attributed to a different conformation of thiophenic rings versus imino-linkages assumed by the polymeric backbone in the two classes of polyazines. Particular attention has been devoted to study the reactivity of mono- and disubstituted dialdehydes toward condensation with nucleophiles displaying different steric hindrance or power. Specifically the study of the reaction onset allowed us to determine the conditions to obtain regioregular monosubstituted polymers even with hydrazine, which is the less hindered and the more powerful nucleophile used. Introduction Two important families of conjugated polymers ex- hibiting interesting optical and electronic properties are those of polyazines (PAZs) and polyazomethines (PAMs), both belonging to the general class of Schiff-base polymers. 1 They are characterized by the presence of HCdN linkages, which are isoelectronic with the HCdCH groups present in many prototypical conju- gated polymers such as polyacetylene and poly(p-phen- ylenevinylene). 2 Conjugated PAZs (Scheme 1), contain direct N-N bonds because they derive from condensations of hy- drazine with aromatic dialdehydes or diketones. On the other hand PAMs (Scheme 1) are the product of con- densation of aromatic dialdehydes with aromatic di- amines hence they are less flexible than analogous PAZs due to the presence of a stiff aromatic moiety between two subsequent nitrogen atoms. Lateral alkyl chains should be present in order to overcome the drawback of the insolubility in organic solvents, which limited the early investigations on these systems. 1e,3 Park et al., among others, inserted (n-alkoxide)methyl side chains on a polyazomethine backbone, improving the solubility of polymers of not too high molecular weight. 4 Conju- gated PAMs, containing only phenylenic moieties, have been synthesized even in a vacuum by using chemical vapor deposition and tested as active layer or hole transport layer in electroluminescent devices. 5 Recently, several conjugated PAMs containing differ- ent aromatic hydrocarbon moieties in the backbone and various side-group substituents have been prepared and used to investigate the effects of the molecular structure on the electronic and optical properties of conjugated polymers. 6 Soluble PAMs in which both phenylenic and thienyl- enic rings constituted the polymeric backbone have been prepared in more recent years by several authors. 7 Moreover, other PAMs and PAZs containing thiophene rings have used for the preparation of optical wave- guides. 8 As regards the alkylic side chains in polymers, it is well-known that their presence modifies electronic and structural properties in polyalkylthiophenes, such an influence is relevant in both substituted PAZs or PAMs although they are more flexible of polyalkylthiophenes. This effect has been studied by Roncali 9 on thienylene- vinylene oligomers, which are comparable with oligo- mers containing imine linkage for both flexibility and electronic character of the double bond. † Istituto di Chimica delle Macromolecole del CNR. ‡ Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita ` di Parma. § Centro Interdipartimentale di Misure “Giuseppe Casnati”, Universita ` di Parma. Scheme 1 353 Macromolecules 1999, 32, 353-360 10.1021/ma9811932 CCC: $18.00 © 1999 American Chemical Society Published on Web 12/29/1998