Self-Assembly DOI: 10.1002/ange.201201436 Self-Organization of Hydrogen-Bonding Naphthalene Chromophores into J-type Nanorings and H-type Nanorods: Impact of Regioisomerism** Shiki Yagai,* Yusaku Goto, Xu Lin, Takashi Karatsu, Akihide Kitamura, Daiki Kuzuhara, Hiroko Yamada, Yoshihiro Kikkawa, Akinori Saeki, and Shu Seki Nature has evolved complex self-organized architectures of pigment assemblages with rational nanoscale topologies and chromophore orientation. [1] Circular architectures of the chlorophyll–protein complexes found in the light-harvesting systems of purple photosynthetic bacteria could be regarded as perfect supramolecular assemblies of pigments in view of not only their topological features but also a functional standpoint. [1b, 2] Sunlight is absorbed uniformly by circularly organized chlorophyll pigments, and the resulting exciton states are delocalized over the closed arrays of chlorophylls. [3] Such exciton delocalization is achieved by partially over- lapped arrays of chlorophyll p systems, which could be referred to as J-type (offset) stacking. [4] In contrast, one- dimensional stacks of largely overlapped p systems, which can be referred to as H-type (face-to-face) stacking, are promising as quasi one-dimensional pathways of mobile charge carriers for organic electronics. [5] Thus, these natural and artificial assemblies of p systems show the importance of simultaneous control over dimensionality of nanostructures and local stacking arrangements to optimize the functionality in the systems. Herein we report that a regioisomerism in specifi- cally designed self-assembling small molecules can offer the aforementioned two extreme nanoarchitectures with favor- able stacking arrangements of their p systems. We have recently reported the self-assembly of p-con- jugated molecules substituted asymmetrically with barbituric acid (BAR) and a wedge-shaped aliphatic tail (“miniden- dron” [6] ). [7] An unique feature of these BAR–p-wedge mol- ecules in nonpolar media is that their ability to form dramatically different nanostructures, namely nanorings [7a,b, 8] and nanorods, [7c] depending on the structure of the p moiety. X-ray diffraction analysis in the mesomorphic state suggested that the BAR–p-wedge molecules form columnar stacks of hydrogen-bonded hexamers (rosettes), which are in nonpolar media solvated to form curved (for nanorings) or straight nanostructures (for nanorods). Although this molecular design is attractive for the construction of well-defined nanostructures consisting of functional p systems, it remains difficult to clarify the structural relationship between mono- mers and assemblies. We now report a striking impact of the regioisomerism of BAR–naphthalene-wedge molecules (Figure 1) on their self-assembled nanostructures, which imparts an important guide to this molecular design toward tailor-made nanostructures. Introduction of BAR and wedge functional moieties into different positions on the naphtha- lene core affords the rosettes with different geometrical features that are favorable for offset or face-to-face stacking arrangements. This geometrical difference at the level of rosettes not only yields perfect nanorings and nanorods, but also enables favorable J- and H-type excitonic coupling of the naphthalene cores, thus exhibiting distinct optical features. Figure 1. Structures of BAR–naphthalene-wedge molecules 1 and 2 and their geometry-optimized structures. [*] Prof.Dr. S. Yagai, Y. Goto, Dr. X. Lin, 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 Dr. D. Kuzuhara, Prof.Dr. H. Yamada Graduate School of Material Science Nara Institute of Science and Technology (NAIST) 8916-5, Takayama-cho, Ikoma, Nara 630-0192 (Japan) Prof. Dr. S. Yagai, Prof. Dr. H. Yamada CREST, JST, 5-3, Yonbancho, Chiyoda-ku Tokyo 102-8666 (Japan) Dr. Y. Kikkawa National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan) Dr. A. Saeki, Prof. Dr. S. Seki Department of Applied Chemistry Graduate School of Engineering, Osaka University 2-1, Yamadaoka, Suita, Osaka 565-0871 (Japan) [**] We are grateful to Prof. Tadashi Mizoguchi and Prof. Hitoshi Tamiaki of Ritsumeikan University for the DLS measurements. This work was partially supported by the Green Photonics Project in NAIST sponsored by the Ministry of Education, Culture, Sports, Science and Technology, MEXT (Japan). Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201201436. A ngewandte Chemi e 6747 Angew. Chem. 2012, 124, 6747 –6751  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim