Photoresponsive Assemblies DOI: 10.1002/ange.201310773 Photocontrol Over Self-Assembled Nanostructures of p–p Stacked Dyes Supported by the Parallel Conformer of Diarylethene Shiki Yagai,* Kazunori Iwai, Mitsuaki Yamauchi, Takashi Karatsu, Akihide Kitamura, Shinobu Uemura, Masakazu Morimoto, Hao Wang, and Frank Würthner Abstract: Diarylethenes (DAEs) have rarely been used in the design of photoresponsive supramolecular assemblies with a well-defined morphology transition owing to rather small structural changes upon photoisomerization. A supramolec- ular design based on the parallel conformation of DAEs enables the construction of photoresponsive dye assemblies that undergo remarkable nanomorphology transitions. The cooperative stacking of perylene bisimide (PBI) dyes was used to stabilize the parallel conformer of DAE through comple- mentary hydrogen bonds. Atomic force microscopy, UV/Vis spectroscopy, and molecular modeling revealed that our DAE and PBI building blocks coassembled in nonpolar solvent to form well-defined helical nanofibers featuring J-type dimers of PBI dyes. Upon irradiating the coassembly solution with UV and visible light in turn, a reversible morphology change between nanofibers and nanoparticles was observed. This system involves the generation of a new self-assembly pathway by means of photocontrol. Dynamic control over the morphologies of molecular assemblies through external stimuli is the key to developing dynamic soft-matter devices. [1] By virtue of various photo- chromic molecules, light is now regarded as the most useful external stimulus for dynamically controlling the morphology and functionality of supramolecular assemblies. [2] Among synthetic photoswitches, diarylethenes (DAEs) are particu- larly appealing because of their remarkably high photo- reactivity and photofatigue resistance and because they show large changes in their optical and electronic properties upon photoisomerization. [3] Nevertheless, they have rarely been used in the design of photoresponsive supramolecular assem- blies, [4] a situation in stark contrast to the many examples of azobenzene-based photoresponsive assemblies. [5] This is attributed to the fact that azobenzenes show large structural changes upon photoisomerization whilst those observed upon DAE photoswitching are rather small, thus enabling even photoinduced ring-closing/opening reactions of DAEs in the bulk state. [6] Most supramolecular assemblies based on DAEs therefore utilize the difference in stacking propensity between the flexible open-ring isomers and the rigid closed- ring isomers to control the assembly and disassembly of one- dimensionally stacked aggregates. [7, 8] A less investigated strategy for inducing drastic morpho- logical changes in the assemblies is the use of the photo- chemically unreactive parallel conformers in equilibrium with the reactive antiparallel conformers in solution (Figure 1 a). If well-defined supramolecular architectures can be designed based on the parallel conformers, the dynamic nature of solution assemblies could allow equilibration with the anti- parallel conformers through aggregate–monomer exchange, thereby leading to a ring-closing photoreaction that would result in a completely different supramolecular structure. The involvement of the parallel conformers has been proposed for several supramolecular systems but the morphologies of those assemblies were not well-defined. [9] We herein demonstrate that the parallel conformation of diarylethenes can be stabilized through the cooperative p–p stacking of noncova- lently bound p-conjugated molecules through specific inter- molecular interactions, thereby producing supramolecular polymers with well-defined one-dimensional nanostructures. The nanostructures dispersed in solution can be reversibly converted into granular aggregates upon the ring-closing/ opening photoreaction of the DAE moieties. Following our earlier work on DAE-photocontrolled merocyanine aggregation [9d] and photochromic DAE–pery- lene bisimide dyads, [10] we herein report photoresponsive supramolecular polymers that make use of the tetratopic receptor 1 o [11] (Figure 1 b) and the tetraphenoxy perylene bisimide ditopic guest PBI, which has a strong propensity to form p–p stacked slipped dimer aggregates. [12] The parallel conformer of 1 o can thus be stabilized by dimeric stacks of PBI (Figure 1 b), and supramolecular polymerization of the resulting 1:2 (1 o /PBI) complex is anticipated to take place even at low concentrations. Because the closed-ring isomer 1 c cannot adopt the specific conformation required to bind the PBI-dimer aggregates, UV irradiation of the supramolecular [*] Prof.Dr. S. Yagai, K. Iwai, M. Yamauchi, Prof.Dr. T. Karatsu, Prof. Dr. A. Kitamura Department of Applied Chemistry and Biotechnology Graduate School of Engineering, Chiba University 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan) E-mail: yagai@faculty.chiba-u.jp Prof. Dr. S. Yagai CREST, JST Chiyoda-ku 102-0075 (Japan) Prof. Dr. S. Uemura Graduate School of Science and Technology, Kumamoto University Kurokami 2-39-1, Chuo-ku, Kumamoto 860-8555 (Japan) Prof. Dr. M. Morimoto Department of Chemistry and Research Center for Smart Molecules Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku Tokyo 171-8501 (Japan) Dr. H. Wang, Prof.Dr. F. Würthner Institut für Organische Chemie and Center for Nanosystems Chemistry, Universität Würzburg Am Hubland, 97074 Würzburg (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201310773. . Angewandte Zuschriften 2640  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2014, 126, 2640 –2644