Pressure Dependence of the Forward and Backward Rates of 9-tert-Butylanthracene Dewar Isomerization

Abstract

9-tert-Butylanthracene undergoes a photochemical reaction to form its strained Dewar isomer, which thermally back-reacts to reform the original molecule. When 9-tert-butylanthracene is dissolved in a polymer host, we find that both the forward and reverse isomerization rates are pressure-dependent. The forward photoreaction rate, which reflects the sum of contributions from photoperoxidation and Dewar isomerization, decreases by a factor of 1000 at high pressure (1.5 GPa). The back-reaction rate, on the other hand, increases by a factor of ∼3 at high pressure. Despite being highly strained and higher volume, the back-reaction reaction rate of the Dewar isomer is at least 100× less sensitive to pressure than that of the bi(anthracene-9,10-dimethylene) photodimer studied previously by our group. These results suggest that the high pressure sensitivity of the bi(anthracene-9,10-dimethylene) photodimer reaction is not just due to the presence of strained four-membered rings but instead relies on the unique molecular geometry of this molecule.

Polymer mechanochemistry-enabled pericyclic reactions

“…109 Within healable materials, induced damage is generally of mechanical nature and hence it was reasonable to assume that the corresponding cycloelimination was also accessible via the application of force. [110][111][112][113][114][115][116][117] Chung and co-workers investigated Scheme 21 Supposed mechanochemical cycloelimination of the nonscissile bridged 1,4-disubstituteted triazole mechanophore in AFM measurements. 102 Scheme 22 Photoinduced [4 + 4] anthracene dimerization and photoas well as mechanochemical cycloelimination.…”

Molecular Origin of Mechanical Sensitivity of the Reaction Rate in Anthracene Cyclophane Isomerization Reveals Structural Motifs for Rational Design of Mechanophores

“…13 Unfortunately, the subsequent design attempt did not show high mechanical sensitivity. 14 This indicates a failure of the employed design strategy based on a perturbative picture of the mechanochemical coupling. 1,3 Such a strategy seeks to minimize the reaction activation volume, while assuming it is independent of pressure.…”

“…Notable examples of the identification of such structural motifs in mechanophores are two recent studies by the groups of Bardeen and Chronister. , The anthracene cyclophane photodimer (Figure ) represents an example of a successful molecular design . Unfortunately, the subsequent design attempt did not show high mechanical sensitivity . This indicates a failure of the employed design strategy based on a perturbative picture of the mechanochemical coupling. , Such a strategy seeks to minimize the reaction activation volume, while assuming it is independent of pressure.…”

“…Notable examples of the identification of such structural motifs in mechanophores are two recent studies by the groups of Bardeen and Chronister. , The anthracene cyclophane photodimer (Figure ) represents an example of a successful molecular design . Unfortunately, the subsequent design attempt did not show high mechanical sensitivity .…”

Universal stress‐sensing dimeric anthracene‐based mechanophore particle fillers incorporated into polyurethane thermoset matrices

“…Its large conjugated structure also allows for its incorporation into many optical‐driven fields, including liquid crystals . Upon application of UV light, anthracene derivatives can photodimerize into a number of structures, with resulting applications in shape memory , self‐healing , and the study of mechanochemical activation . Anthracene has a much higher absolute fluorescence quantum yield compared with other mechanophores, due to its large conjugated system, and thus it is a desirable candidate for mechanochemical signaling via fluorescence generation .…”