A novel procedure has been developed for the Gilch reaction leading to poly(p-phenylene vinylenes) (PPVs). In the first step, selective activation of the starting material is achieved at low temperature. Subsequently, controlled chain growth is induced by lighting the α-halo-p-quinodimethane monomer. In contrast to the thermal Gilch polymerization, the photoinduced process allows adjusting crucial parameters such as intensity and energy of light. The progress of PPV formation can be followed visually or by in situ UV-vis spectroscopy. If the polymers are formed under appropriate conditions, they show very high molar masses, polydispersities in the common range, and higher constitutional homogeneity than thermally grown PPVs.

For the first time, the successful Gilch synthesis of poly(ortho-phenylene vinylenes) (ortho-PPVs) is reported. The molar mass of the constitutionally homogeneous ortho-PPVs reaches values as high as Mw ≈ 300 000 Da. The ortho-connectivity of the repeating units forces the chains to assume closely packed conformations even in good solvents. Significant perturbation of the π-electron systems and considerable shortening of the conjugation lengths are the consequences. UV-vis absorption and photoluminescence maxima consequently are shifted clearly toward shorter wavelengths compared to, e.g., classic para-PPVs.

Front Cover: Geometric squeezing of the poly(phenylene vinylene) repeating units from conventional para‐connectivity to the ortho isomeric state induces considerable perturbation of the delocalized π–electron system. Shortened conjugation lengths and significant blue‐shifts of UV‐vis absorption and photoluminescence characteristics are the consequences. Creative graphic support in catchy visualization of that squeezing effect provided by Mr. Christian Krupp, WKC project, is gratefully acknowledged. Further details can be found in the article by V. Rittscher, S. Kuch, and M. Rehahn* on page 814.