Hiroto S, Wakita M, Chujo M. A Strategy for Polar Crystals with Dipolar Heterohelicenes.
Chem Asian J 2022;
17:e202200808. [PMID:
36065075 DOI:
10.1002/asia.202200808]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Revised: 09/03/2022] [Indexed: 11/03/2022]
Abstract
Polar crystals have attracted interest for the applications to polar materials with piezo- and pyroelectricity, and second harmonic generation. Despite their potential utility for flexible polar materials, a strategy for ordering polar helicenes have remained elusive. Here, we demonstrate creation of polar crystal with unsymmetrically substituted aza[5]helicenes tuned by substituents. The usymmetric aza[5]helicenes have been prepared through regioselective monoprotiodesilylations. We disclosed triisopropylsilyl-substituted derivatives show 1D chain columnar packings. In particular, enantiopure crystals showed spontaneous polarization. Optical and single-crystal X-ray diffraction experiments with other derivatives, as well as theoretical calculations, revealed that the presence of triisopropylsilyl or electron-withdrawing aryl substituents is essential for forming the 1D chain columnar structure. Hirshfeld surface analyses further showed that CH-π interactions between 1D chain columns regulate the polar assembly. Finally, we determined the polarizability of the nitro derivative by ab initio calculation to be 4.53 µC/cm 2 . This value corroborates the first example of a spontaneously polar crystal of helicenes. We believe that this study will contribute to the development of polar materials from organic molecules.
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