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Evaluating photodimerization of 6-methylcoumarin mediated by cucurbit[8]uril through mechanical grinding – Supramolecular effects of additives

Paper ID Volume ID Publish Year Pages File Format Full-Text
27834 44045 2013 6 PDF Available
Title
Evaluating photodimerization of 6-methylcoumarin mediated by cucurbit[8]uril through mechanical grinding – Supramolecular effects of additives
Abstract

6-Methylcoumarin (1) upon mechanical grinding with cucurbit[8]uril (CB[8]) or other additives (e.g. thiourea) showed enhanced photodimerization efficiency with exclusive formation of head-to-head photodimer. Mechanical grinding of 1 with CB[8] resulted in host–guest interaction with red-shift fluorescence in the solid-state. This red shift in fluorescence emission is similar to the red-shifted emission observed for CB[8]–1 host–guest complex in solution at 298 K. Phosphorescence emission profile in the solid state at 77 K for mechanically ground 1 with CB[8] was similar to the phosphorescence profile observed for CB[8]–1 host–guest complex at 77 K. Single crystal X-ray determination of 1 from water reveals that the coumarins are oriented in a head-to-head fashion with the distance between the double bonds being 4.695 Å, a distance that is greater than the required Schmidt distance of 4.2 Å for efficient photodimerization in the crystalline state. Enhancement of photoreactivity of 1 upon mechanical grinding with additives appears to be the result of a combination of factors, viz.: (a) crystalline imperfection/defects that are likely formed during mechanical grinding and/or; (b) formation of a new phase due to mechanical grinding (we were not able to observe any noticeable change in crystallinity, while the formation of an amorphous phase could not be ruled out completely).

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The photochemistry and photophysics of 6-methylcomarin 1 are influenced by mechanical grinding with cucurbit[8]uril. ► Bathochromic shift was observed in the room temperature fluorescence spectra of 1 upon mechanical grinding with CB[8]. ► A red shift in the phosphorescence spectra of 1 was observed at 77 K upon mechanical grinding with CB[8]. ► 6-Methylcoumarin 1 is not photoreactive in the solid-state but the photodimerization efficiency was enhanced upon mechanical grinding of 1 leading to the formation of head-to-head photoproduct.

Keywords
Photodimerization; Cucurbit[8]urils; Supramolecular confinement effects; Solid state mechanical grinding; Solid state photoreactions; Crystalline media
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Evaluating photodimerization of 6-methylcoumarin mediated by cucurbit[8]uril through mechanical grinding – Supramolecular effects of additives
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 255, 1 March 2013, Pages 10–15
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
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Any Questions? feel free to contact us