A diffuse reflectance comparative study of benzil inclusion within microcrystalline cellulose and beta-cyclodextrin

Area of Science:

• Photochemistry
• Photophysics
• Solid-state chemistry

Background:

• Benzil exhibits conformational diversity in the ground state.
• Solid supports influence photochemical and photophysical behaviors.
• Room temperature phosphorescence is a key property.

Purpose of the Study:

• Investigate benzil's photochemical and photophysical processes on microcrystalline cellulose and beta-cyclodextrin.
• Characterize the influence of these solid supports on benzil's excited states and degradation pathways.
• Determine the role of host-guest interactions in modulating benzil's properties.

Main Methods:

• Diffuse reflectance spectroscopy
• Laser-induced transient absorption spectroscopy
• Room temperature phosphorescence measurements
• Product analysis via chromatography and spectroscopy

Main Results:

• Benzil exists as a mixture of conformers on both supports, favoring skew conformations.
• Room temperature phosphorescence was observed for benzil on both cellulose and beta-cyclodextrin.
• Beta-cyclodextrin enhanced benzil's phosphorescence lifetime, indicating favorable encapsulation.
• Triplet-triplet absorption and ketyl radical formation were observed for benzil on cellulose.
• Benzoyl radicals were detected for benzil in beta-cyclodextrin.
• Main photoproducts were benzoic acid and benzaldehyde, with variations in their ratio and formation of benzyl alcohol on cellulose.

Conclusions:

• Solid supports significantly affect benzil's photophysical properties and photochemical reactivity.
• Beta-cyclodextrin effectively enhances benzil's room temperature phosphorescence through host-guest complexation.
• Cellulose promotes different radical pathways and product distributions compared to beta-cyclodextrin.
• Understanding these host-guest interactions is crucial for controlling benzil's photochemistry in solid matrices.