This article features recent advances in the synthesis of conjugated polymers via a controlled polymerization. These polymerizations typically rely on transition metal catalyzed cross coupling reactions. The mechanisms of the polymerization protocols are discussed in detail. An overview of all possible protocols and all homopolymers that have been investigated is given. Next, the synthesis of copolymers-random, gradient and block copolymers-is reviewed. Another advantage of a controlled polymerization is the possibility to introduce specific functional groups, either at the beginning of each polymer chain by the use of an external initiator, or at the end of the polymer chain using an endcapper. Finally, topologies different from simple linear polymer chains are discussed. This feature article is complementary to other recent review articles on this topic. 1,2

Solubilized poly(3-alkylthiophene)s are known to self-assemble into well-ordered supramolecular aggregates upon lowering the solvent quality. This supramolecular organization largely determines the optical and electronic properties of these polymers. However, despite numerous studies the exact mechanism and kinetics of the aggregation process and the role of external stimuli are still poorly understood. Classical characterization techniques such as electronic spectroscopy, dynamic light scattering, and diffraction-based techniques have not been able to provide a full understanding. Here we use second-harmonic scattering (SHS) and third-harmonic scattering (THS) techniques to investigate this supramolecular aggregation mechanism. Our results indicate that the actual supramolecular aggregation is preceded by the formation of structured polymer-solvent clusters consistent with a nonclassical crystallization pathway.

Through the incorporation of chiral and achiral poly­(3-alkylthiophenes) (P3ATs) into a star-shaped system, a well-defined supramolecular organization is obtained lacking the unfavorable linear lamellar structure typically obtained for P3AT. Through the combination of a controlled chain-growth polymerization and efficient postpolymerization and click reactions, well-defined star-shaped P3ATs with a low dispersity of 1.1 were obtained. The combination of UV–vis, circular dichroism (CD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) measurements showed the formation of a strong (chiral) supramolecular organization into fibers, different and stronger than those obtained with the linear P3ATs. The fact that the width of the fibers is in good agreement with the width of a single star-shaped P3AT excludes the formation of a linear lamellar structure. Furthermore, the particular supramolecular organization of the star-shaped polymers, which appears thanks to the precision polymer synthesis, triggers properties of the arms of the star-shaped molecule that are not present in the individual arms.

Chirality is typically expressed in chiral molecules, including polymers. In this work, we demonstrate that chirality can also be expressed in a polymer molecule that does not contain any excess of chiral centers; in this specific material the chirality is evoked by a specific order of manipulations ("events"). The polymer studied is an allconjugated block copoly(3-alkylthiophene), in which the first block contains exactly the same amount of (S)-enantiomers as the second block (R)-enantiomers. Moreover, to introduce a distinct difference in solubilityrequired to have multiple consecutive eventsthe S-block is composed of S-monomers copolymerized with octyl-functionalized thiophene monomers, while the R-block is composed of R-monomers in combination with amine-functionalized thiophene monomers. By making use of the difference in solubility of both blocks, a chiral response can be evoked from this polymer without the need of a chiral trigger.

The supramolecular organization of star-shaped polythiophenes was investigated in a solvent/nonsolvent system and upon cooling. Both systems yield entirely different supramolecular aggregates. Classical characterization techniques can give some insight; the exact mechanism is currently not understood. By introducing second- and third-harmonic light scattering and its combination with other optical techniques, we were able to fully investigate the evolution of the supramolecular organization in both regimes. This approach allowed an unprecedented insight into the different stages of the process. A markedly different assembly mechanism is proposed for both regimes, which results in a different supramolecular organization of the polymer.