On the basis of an extended series of monodisperse oligomers of the dialkoxy-substituted phenyleneethenylenes la-i the Eqs.(3) and (4) were conceived in order to determine the limiting values of the energies Ei and the wavelengths di of the W / v i s absorption. The convergence of the Ei and l i values with a growing number n of repeating units pennits a precise prediction of the Ei,,,, and ,Ii,,,, values of the corresponding polymer 1 j as well as a statement about the overall effect of conjugation mi and the effective conjugation length ECL. A great variety of different conjugated oligomers 2-14 can be evaluated by the same algorithm. Acta Polymer., 48,379-384 Q VCH Verlagsgesellschaft mbH, D-69451 Weinheim 1997 0323-7648/97/0808-0379$17.50+.50/0 Acta Polymer., 48,379-384 (1997) Effective conjugation length and UV/vis spectra of oligomers 383

Stilbenes and compounds containing stilbene units in their structures form the material basis for numerous research projects in photophysics and photochemistry. Moreover, because these compounds are easy to synthesize and are thermally and chemically stable, they are taking on an increasingly prominent role in the area of materials science investigations into optical, electrical. and optoelectronic properties. In accordance with the interdisciplinary nature of such studies, this article aims to provide a bridge extending from molecular theory and photophysical measurements, through preparative applications, to material effects and their potential technical applications.

Conjugated oligomers represent a prominent class of compounds from a viewpoint of their theory, synthesis, and applications in materials science. Push-pull substitution with an electron donor D at one end of the conjugation and an electron acceptor A at the other end results in them having outstanding optical and electronical properties. This Review highlights fundamental synthetic strategies for the preparation of such oligomers with n repeat units (n=1, 2, 3, 4, ..) and the rules that govern their linear and nonlinear optical properties (absorption, frequency doubling and tripling). The unification of chemical, physical, and theoretical aspects with an interdisciplinary image of this class of compounds is attempted herein.

Ring around the roses: The ipso substitution of benzene rings makes a simple and efficient synthesis of pillar[n]arenes (n=5, 6) possible. Pillar[6]arenes (see picture) and pillar[5]quinone, an oxidation product of pillar[5]arene, are novel, highly promising host systems for host–guest chemistry.

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