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Substituted and nonsubstituted aniline oligomers were theoretically investigated. Aniline oligomers with a dicyanoethenyl acceptor group attached at a terminal site of each known structure (emeraldine, pernigraniline, and leucoemeraldine forms), contributing to obtain large first hyperpolarizabilities. The effect of oligomer size on the nonlinear responses was also investigated by considering oligomers with different chain length (tetramers and octamers). The magnitudes of ␤ calculated for the functionalized and nonfunctionalized octamers were larger than for the tetramers and their substituted oligomers. The substituted pernigraniline octamer presented the largest ␤ value among the investigated aniline oligomers. The results of the AM1/TDHF calculations suggest that these aniline-based materials can be good candidates for second-order nonlinear optical materials.

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The interest in the study of oligomers has been motivated mainly because of their solubility in common solvents and also their capacity to be crystallized, which allowed for chemical processing leading to important applications in the area of material sciences. In this work, we carried out an investigation of polydiethynylsilane (PDES) decamers substituted with electron donor (D) and acceptor (A) groups, which is certainly of relevance, once PDES itself is known to display large third‐order optical susceptibility. Therefore, density functional theory calculations of static first hyperpolarizability (β) were performed using various functionals with the 6‐31G(d) basis set along with correlated MP2 calculation used as reference for comparison. The influence of A and D substituents on the magnitude of β was investigated by matching the acceptor (dicyanovinyl, nitrobenzene) and donor (propyl, propoxy, and phenylamine) groups attached at both ends of the oligomer. The largest β value was predicted for the derivative having the phenylamine and dicyanovinyl groups, which is around 30 times the relative value for the nonsubstituted decamer, what is a very impressive enhancement reported for the first time in the literature, strongly suggesting that disubstituted diethynylsilane decamers are potential building blocks for molecular‐based materials with second‐order nonlinear responses. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1410–1419, 2011