Photosalience and Thermal Phase Transitions of Azobenzene- and Crown Ether-Based Complexes in Polymorphic Crystals.
J Am Chem Soc
; 145(39): 21378-21386, 2023 Oct 04.
Article
en En
| MEDLINE
| ID: mdl-37733877
ABSTRACT
Stimuli-responsive molecular crystals have attracted considerable attention as promising smart materials with applications in various fields such as sensing, actuation, and optoelectronics. Understanding the structure-mechanical property relationships, however, remains largely unexplored when it comes to functionalizing these organic crystals. Here, we report three polymorphic crystals (Forms A, B, and C) formed by the non-threaded complexation of a dibenzo[18]crown-6 (DB18C6) ether ring and an azobenzene-based ammonium cation, each exhibiting distinct thermal phase transitions, photoinduced deformations, and mechanical behavior. Structural changes on going from Form A to Form B and from Form C to Form B during heating and cooling, respectively, are observed by single-crystal X-ray crystallography. Form A shows photoinduced reversible bending, whereas Form B exhibits isotropic expansion. Form C displays uniaxial negative expansion with a remarkable increase of 44% in thickness under photoirradiation. Force measurements and nanoindentation reveal that the soft crystals of Form A with a low elastic modulus demonstrate a significant photoresponse, attributed to the non-threaded molecular structure, which permits flexibility of the azobenzene unit. This work represents a significant advance in the understanding of the correlation between structure-thermomechanical and structure-photomechanical properties necessary for the development of multi-stimulus-responsive materials with tailored properties.
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MEDLINE
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En
Revista:
J Am Chem Soc
Año:
2023
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Article
País de afiliación:
Taiwán