Self-Assembly DOI: 10.1002/anie.201209004 Aggregation-Driven Reversible Formation of Conjugated Polymers in Water** Dainius Janeliunas, Patrick vanRijn, Job Boekhoven, Christophe B. Minkenberg, Jan H. van Esch,* and Rienk Eelkema* Herein we show how the formation of dynamic covalent conjugated polymers in water can be achieved by stabilizing reversible covalent bonds through molecular self-assembly. Conventional conjugated macromolecules offer rich optical properties and charge mobility along the polymer backbone through extensive covalent p conjugation, but their behavior is typically rather static and they often require tedious synthetic methodologies. [1] In contrast, supramolecular poly- mers can be highly dynamic and responsive, and can be made by self-assembly of small building blocks. [2] However, these noncovalently linked polymers lack an efficient p-conjugated backbone and the associated control over optical properties. [3] Merging features of both polymer classes, dynamic covalent conjugated polymers potentially offer the covalent, fully conjugated backbone of a conventional polymer, combined with the ease of formation and dynamics of supramolecular polymers. [4] Besides their typical applications in optoelec- tronic devices, conjugated polymers in aqueous environments could find use in biomedical imaging and sensors, [5] as well as chemical [6] and pH [7] detectors. In these fields, aqueous supramolecular conjugated polymers have already attracted great attention over the past decades [3] for their potential application in light-emitting devices, [8] organic transistors, and photovoltaics. [9] Dynamic covalent chemistry is shown to be a powerful concept for the construction of adaptive and responsive molecular systems, [10] and has occasionally been used for the synthesis of reversible conjugated macromole- cules, albeit mostly in organic solvents and not in water. [11] Herein we report the reversible formation of a fully p- conjugated dynamic covalent polymeric system in aqueous media. Imine bonds, obtained through the well-known reversible condensation reaction of amines with aldehydes, offer a reversible molecular connection which potentially allows a fully conjugated path between aromatic building blocks. For this reason, we explored the formation of imine- based dynamic covalent conjugated polymers. In general, the degree of polymerization in reversible polymerizations depends on the equilibrium constant of the reversible reaction and the monomer concentration. [2, 12] The equilibri- um constant for the formation of imines from aromatic aldehydes and aromatic amines in water, in contrast to organic solvents, [13] is very small. [14] Therefore such polymer- ization in water will generally result in the formation of very short oligomers with subordinate properties. However, we and others have recently shown that these reversible bonds gain stability through self-assembly in supramolecular aggre- gates. [15] Accordingly, self-assembly of the formed polyimine oligomers should lead to stabilization of the imine bonds, thereby enabling the formation of longer conjugated poly- mers in water. For this purpose, we designed the following system for construction of potentially self-assembling p- conjugated imine polymers. The present study requires two types of monomers: water- soluble bis(aldehyde)s and bis(amine)s, both with a conju- gated pathway between the termini (Figure 1 a). Figure 1. a) Formation of polymers P1, P2, and P3 from the terthio- phene bis(aldehyde) A and aromatic bis(amine)s 1, 2, and 3. b) UV/ Vis absorption of 1 mm aqueous solutions of A (green line), P1 (black), P2 (red), and P3 (blue). Inset: photographs of typical aqueous samples of A, P1, P2, and P3. [*] D. Janeliunas, Dr. P. van Rijn, Dr. J. Boekhoven, Dr. C. B. Minkenberg, Prof. Dr. J. H. van Esch, Dr. R. Eelkema Department of Chemical Engineering Delft University of Technology Julianalaan 136, 2628 BL, Delft (The Netherlands) E-mail: j.h.vanesch@tudelft.nl r.eelkema@tudelft.nl [**] We are grateful to Lars van der Mee for his help with the synthesis, and Joost L. J. van Dongen and Prof. Luc Brunsveld (Eindhoven University of Technology) for GPC and MALDI-TOF analyses. This work was supported by the Netherlands Organization for Scientific Research (NWO Vici and Veni grants) and the European Commis- sion (Marie Curie European Reintegration Grant). Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201209004. A ngewandte Chemi e 1 Angew. Chem. Int. Ed. 2013, 52,1–5  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! Ü Ü