German Edition: DOI: 10.1002/ange.201602502 Solid-State Fluorescence International Edition: DOI: 10.1002/anie.201602502 Engineering Stacks of V-Shaped Polyaromatic Compounds with Alkyl Chains for Enhanced Emission in the Solid State Shoya Sekiguchi, Kei Kondo, Yoshihisa Sei, Munetaka Akita, and Michito Yoshizawa* Abstract: A V-shaped bisanthracene derivative with three butyl groups formed two types of emissive solids that display bluish green and blue fluorescence (F F = 72 and 32 %, respectively), depending on the preparation conditions. The crystal and powder X-ray analyses reveal that the highly emissive solid adopts a head-to-head arrangement with discrete stacks of the anthracene moieties, whereas the moderately emissive solid adopts a head-to-tail arrangement without the stacks. The obtained molecular arrangements are transformed by thermal stimuli accompanying the change in fluorescence. Further- more, large enhancements of dye emissions (12–45-fold) through highly efficient host–guest energy transfer were achieved in the solid state by adding minute amounts of various fluorescent dyes (e.g. rubrene and Nile red) to the V- shaped compound. Polyaromatic compounds with peripheral substituents often form well-ordered columnar stacks in the solid state (Fig- ure 1 a). [1] However, the emissive ability of the polyaromatic moieties found in dilute solutions is apt to be lost or weakened in such infinite structures owing to nonradiative decay of the excited states through extensive aromatic–aromatic interac- tions. Full encirclement of polyaromatic compounds by molecular capsules [2, 3] or bulky substituents [4–6] can prevent infinite stacking of the fluorophores (Figure 1 b) so that most of them show simple emissions from the monomeric species. In contrast, dimeric stacks of polyaromatic molecules have received considerable attention, because their structures sometimes exhibit intriguing fluorescence behavior derived from the formation of excimers. [7] However, there is no general and rational approach to prepare highly fluorescent dimeric stacks of polyaromatic compounds through non- covalent interactions. [8] To exploit a new class of polyaromatic solids with a greater emissive ability, we designed a V-shaped polyaromatic compound bearing bulky substituents on the convex side to engineer 1) the dimeric stack of the bent polyaromatic frameworks (Figure 1 c) and 2) the layered arrays of the polyaromatic dimers through intermolecular interactions between the substituents. Here we report the unusual emission behavior of V-shaped bisanthracene deriv- ative 1 with three butyl groups (Figure 1d) in the solid state. The V-shaped compound forms two different types of solids depending on the preparation conditions. The solid with a head-to-head arrangement (Figure 1 c) shows strong bluish green fluorescence (F F = 72 %) as a consequence of finite stacks of the anthracene moieties. In contrast, the other solid with a head-to-tail arrangement shows moderate blue fluo- rescence (F F = 32 %). The molecular arrangement and emis- sive states can be changed by thermal stimuli. In addition, the solid-state emission properties of various fluorescent dyes (e.g. rubrene and Nile red) are greatly enhanced (12–45-fold) by mixing them with the bisanthracene derivative upon single irradiation with UV light (e.g. l = 368 nm), because of highly efficient energy transfer from the anthracene moieties to the dyes. In this study, we initially focused on a V-shaped poly- aromatic framework [9] composed of two anthracene panels linked by a meta-phenylene spacer with hydroxy groups because of its rigid and bent structure as well as appropriately stable and fluorescent character. [10] We expected that the functionalization of the bent framework with three alkyl chains on the convex side could generate highly emissive solids through engineered aromatic–aromatic (i.e. p-stacking) and alkyl–alkyl (i.e. van der Waals) interactions. The n-butyl group was employed as a suitable substituent to fully cover the exo-polyaromatic surface of the V-shaped framework Figure 1. Schematic representations of a) the infinite stack and b) the isolation of planar polyaromatic compounds with substituents, and c) the discrete stack of bent polyaromatic compounds with substitu- ents on the convex side. d) V-Shaped bisanthracene derivative 1 designed herein and e) the optimized structure (DFT calculation, B3LYP/6-31G* level). [*] S. Sekiguchi, Dr. K. Kondo, Dr. Y. Sei, Prof.Dr. M. Akita, Dr. M. Yoshizawa Chemical Resources Laboratory Tokyo Institute of Technology 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan) E-mail: yoshizawa.m.ac@m.titech.ac.jp Supporting information for this article can be found under: http://dx.doi.org/10.1002/anie.201602502. Angewandte Chemie Communications 6906 # 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2016, 55, 6906 –6910