Pseudopolymorphism of a luminescent anthracene‐pentiptycene π‐system: The persistent alkyl‐pentiptycene threading mode

• Published in: Journal of the Chinese Chemical Society (Taipei) Vol. 69; no. 10; pp. 1719 - 1729
• Main Authors: Tsai, Chia‐Ying, Cheng, Chiao‐Min, Ho, Yu‐Chieh, Hsu, Ying‐Feng, Liu, Yi‐Hung, Peng, Shie‐Ming, Yang, Jye‐Shane
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley‐VCH Verlag GmbH & Co. KGaA 01.10.2022; Wiley Subscription Services, Inc
• Subjects: Anthracene; Chloroform; Crystallization; Crystals; Fluorescence; Hexanes; Luminescence; Optical properties; Photochemistry; Solvents; Spectroscopy; Structural stability; Supramolecular chemistry; Unit cell
• ISSN: 0009-4536; 2192-6549
• DOI: 10.1002/jccs.202200366

Understanding the crystal packing behavior of a luminescent π‐conjugated system would facilitate the design of crystals of the desired luminescence properties. Crystal pseudopolymorphism provides a great opportunity for such a purpose and meanwhile for tuning the solid‐state luminescence properties of a molecular system via crystallization in different solvents. Herein, we report an example of structural modification that converts a polymorphic anthracene‐pentiptycene π‐system (1) into a pseudopolymorphic counterpart (2), which displays polymorph‐dependent fluorescence color and [4 + 4] photodimerization activity. The five pseudopolymorphs of 2 (crystal notation 2/Solvent, and Solvent = THF, Hex, CHCl3, DCM, and MeOH) have a common feature of forming one‐dimensional (1D) columnar alkyl‐pentiptycene threading mode. The subsequent packing of the 1D columns depends on the size of the included solvents, leading to two major types of pentiptycene‐based framework. One of the frameworks possesses 1D solvent channels that account for 14–18% of the unit cell volume, and the other type has small solvent cavities. A crystal with partial hexane inclusion (i.e., 2/Hex') is also obtained, which provides insights into the stability of the apohost structure. Intriguing solvent guest effects on the fluorescence properties of 2/Solvent are also noted. Six pseudopolymorphs of the title compound highlight the primary effect of alkyl‐pentiptycene threading interactions and the secondary effect of solvent size in the crystal packing, luminescence properties, and [4+4] photodimerization activity.