Mechanical Properties and Photomechanical Fatigue of Macro- and Nanodimensional Diarylethene Molecular Crystals

Abstract

The diarylethene derivative, 1,2-bis­(2,4-dimethyl-5-phenyl-3-thienyl)­perfluorocyclopentene, undergoes a reversible photoisomerization between its ring-open and ring-closed forms in the solid-state and has applications as a photomechanical material. Mechanical properties of macrocrystals, nanowire single crystals, and amorphous films as a function of multiple sequential UV and visible light exposures have been quantified using atomic force microscopy nanoindentation. The isomerization reaction has no effect on the elastic modulus of each solid. But going from the macro- to the nanowire crystal results in a remarkable over 3-fold decrease in the elastic modulus. The macrocrystal and amorphous solids are highly resistant to photomechanical fatigue, while nanowire crystals show clear evidence of photomechanical fatigue attributed to a transition from crystal to amorphous forms. This study provides first experimental evidence of size-dependent photomechanical fatigue in photoreactive molecular crystalline solids and suggests crystal morphology and size must be considered for future photomechanical applications.

Supramolecular Modification of a Metal-Organic Framework Increases Flexibility and Switchability: Experimental Insights into Structural Deformation of ZIF-8

“…Thus, the elastic modulus results for nanocrystals are expected to yield an average response reflective of all planes of the bulk crystal, as previously described. 30,31,[36][37][38] The average elastic modulus and standard deviation values were 0.7 ± 0.2 and 2.1 ± 0.8 GPa for base-modified and unmodified ZIF-8 nanocrystals, respectively. Thus, in situ synthesis of ZIF-8 nanocrystals with triethylamine (Et3N) modulator resulted in a marked three-fold decrease in elastic modulus and a corresponding increase in framework flexibility compared to unmodified ZIF-8.…”

“…AFM nanoindentation showed force versus indentation depth plots that were purely elastic, enabling us to fit the stress-strain curve to the JKR elastic contact model. 30,31,[36][37][38] For a given indentation depth past 3 nm, the force applied to the solids was about three times more in the unmodified nanocrystals of ZIF-8 compared to the modified samples (Figure 2c). The average elastic moduli of the nanocrystals were statistically similar within each sample type and were combined into two separate histograms (Figure 2d).…”

“…AFM nanoindentation was performed by recording force versus vertical piezo displacement curves to generate force-indentation distance plots that were used to determine the elastic modulus (i.e., Young's modulus, stiffness, rigidity) 30,31,[36][37][38] of individual base-modified ZIF-8 nanocrystals and compared to the mechanical properties of unmodified nanocrystals. Repeated force-indentation plots were collected on eleven individual amine-modified and fourteen unmodified nanocrystals of ZIF-8 at two-four different positions in the approximate center of each crystal.…”

“…The acquisition of the force plots and corresponding data analysis were carried out as reported in our previous works. 30,31,[36][37][38] Ar gas sorption measurements were performed on modified and unmodified nanocrystals of ZIF-8 using an Autosorb iQ (Anton Paar QuantaTec, Boynton Beach, FL) with a MP (micropore) analysis station. Samples (100 mg) were activated by degassing for 12 hours at 100 °C followed by ensuring the rise in pressure was no greater than 21 mtorr/min while at activation temperature.…”

“Click-switch” – one-step conversion of organic azides into photochromic diarylethenes for the generation of light-controlled systems

“…Since their first description in the late 1960s, literally thousands of DAE derivatives have been synthesized, characterized, and applied in many fields. 1 In addition to their originally intended application in optical information storage materials, DAEs have been incorporated into biomolecules, 2 molecular machines, 3–5 crystals, 6 surfaces 7 and nanoparticles, 8–10 as the reversible induction of structural changes by light promises attractive options for the modulation of chemical, physical, or biological properties. The incorporation of DAEs into target molecules typically requires multi-step organic synthesis, thereby limiting the application of these compounds.…”