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Axial chiral bisbenzophenazines: solid-state self-assembly via halide hydrogen bonds triggered by linear alkanes.

Metz AE, Podlesny EE, Carroll PJ, Klinghoffer AN, Kozlowski MC - J. Am. Chem. Soc. (2014)

Bottom Line: These weak interactions can be disrupted mechanically, causing the material to revert to the amorphous form.Notably, the interchange between the amorphous and crystalline forms is readily reversible and is easily observed by characteristic colorimetric changes.Measurements via photoimage processing reveal that the degree of color change is dictated by the type of alkane employed.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.

ABSTRACT
An axial chiral tetrachlorinated bisbenzo[a]phenazine has been discovered that undergoes an alkane-induced shift in the solid state from a disordered amorphous form to an ordered polycrystalline form. This phase transition is caused by the formation of pores that accommodate linear alkanes of varying lengths with a very strong affinity as judged by differential scanning calorimetry. Single crystal X-ray structure analysis revealed that a series of weak phenolic OH···Cl hydrogen bonds dictates the pore structure. These weak interactions can be disrupted mechanically, causing the material to revert to the amorphous form. Notably, the interchange between the amorphous and crystalline forms is readily reversible and is easily observed by characteristic colorimetric changes. Measurements via photoimage processing reveal that the degree of color change is dictated by the type of alkane employed.

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Mechanochromism of 1a. (A) Solid before shearing(Y-O form). (B) Production of R-O form byshearing. (C) Reversal of R-O solid to the Y-O solid by suspension in n-hexane.
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fig2: Mechanochromism of 1a. (A) Solid before shearing(Y-O form). (B) Production of R-O form byshearing. (C) Reversal of R-O solid to the Y-O solid by suspension in n-hexane.

Mentions: Precipitation of tetrachlorinated 1a from a solution in acetone with hexanes generated a yellowsolid (Y-O, Figure 2A) that wasfound to be mechanochromic. Specifically, shearing the sample betweenglass slides led to a color change from yellow-orange to red-orange(R-O, Figure 2B). This characteristicwas not seen with 1b–f, 2, or 3, indicating that the chloro groups, phenol groups,dimeric assembly, and regiochemistry are all critical to this property.The 1H NMR spectrum of Y-O revealed a complexwith hexane, and the spectrum of R-O confirmed that 1a remains intact. In addition to production of R-O by mechanical stress, concentration of 1a from a homogeneoussolution in MeOH also produces R-O. Interestingly, theeffect of the mechanical action could be reversed with solvent. Exposureof the sheared solid (or R-O obtained from MeOH) to alkanesolvent or vapor reverts the sample to the Y-O form (Figure 2C).


Axial chiral bisbenzophenazines: solid-state self-assembly via halide hydrogen bonds triggered by linear alkanes.

Metz AE, Podlesny EE, Carroll PJ, Klinghoffer AN, Kozlowski MC - J. Am. Chem. Soc. (2014)

Mechanochromism of 1a. (A) Solid before shearing(Y-O form). (B) Production of R-O form byshearing. (C) Reversal of R-O solid to the Y-O solid by suspension in n-hexane.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4353019&req=5

fig2: Mechanochromism of 1a. (A) Solid before shearing(Y-O form). (B) Production of R-O form byshearing. (C) Reversal of R-O solid to the Y-O solid by suspension in n-hexane.
Mentions: Precipitation of tetrachlorinated 1a from a solution in acetone with hexanes generated a yellowsolid (Y-O, Figure 2A) that wasfound to be mechanochromic. Specifically, shearing the sample betweenglass slides led to a color change from yellow-orange to red-orange(R-O, Figure 2B). This characteristicwas not seen with 1b–f, 2, or 3, indicating that the chloro groups, phenol groups,dimeric assembly, and regiochemistry are all critical to this property.The 1H NMR spectrum of Y-O revealed a complexwith hexane, and the spectrum of R-O confirmed that 1a remains intact. In addition to production of R-O by mechanical stress, concentration of 1a from a homogeneoussolution in MeOH also produces R-O. Interestingly, theeffect of the mechanical action could be reversed with solvent. Exposureof the sheared solid (or R-O obtained from MeOH) to alkanesolvent or vapor reverts the sample to the Y-O form (Figure 2C).

Bottom Line: These weak interactions can be disrupted mechanically, causing the material to revert to the amorphous form.Notably, the interchange between the amorphous and crystalline forms is readily reversible and is easily observed by characteristic colorimetric changes.Measurements via photoimage processing reveal that the degree of color change is dictated by the type of alkane employed.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.

ABSTRACT
An axial chiral tetrachlorinated bisbenzo[a]phenazine has been discovered that undergoes an alkane-induced shift in the solid state from a disordered amorphous form to an ordered polycrystalline form. This phase transition is caused by the formation of pores that accommodate linear alkanes of varying lengths with a very strong affinity as judged by differential scanning calorimetry. Single crystal X-ray structure analysis revealed that a series of weak phenolic OH···Cl hydrogen bonds dictates the pore structure. These weak interactions can be disrupted mechanically, causing the material to revert to the amorphous form. Notably, the interchange between the amorphous and crystalline forms is readily reversible and is easily observed by characteristic colorimetric changes. Measurements via photoimage processing reveal that the degree of color change is dictated by the type of alkane employed.

Show MeSH