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Water is an under-appreciated reaction medium that has been shown to facilitate photodimerization reactions. Despite having a low formal concentration, hydrophobic nature of organic compounds could lead to higher local concentrations, thereby favoring their cycloaddition. In contrast, photodimerization reactions are unlikely to occur in organic solvents under similar conditions. This study explores the supramolecular assembly of small organic molecules in water, focusing on their role in promoting photodimerization reactions. NMR spectroscopy, molecular dynamics simulations, and ab initio calculations were used to examine the dynamic interactions between indene and its aggregated state in water. Quantum mechanical calculations suggest that the stacking of indene with an antiparallel-displaced orientation is the most stable configuration, and MD simulations support the role of water in promoting aggregation. NMR results confirm the existence of indene aggregates, and 2D NMR reveals dynamic exchange between monomer and aggregate states. The study elucidates the complex dynamics of indene aggregation and its impact on photodimerization, providing insights into designing other photoreactions in water.
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Water: An underappreciated reaction medium for photodimerizations,
Organic solvents have been the sought-after medium to achieve light initiated transformations in laboratories and industries. Given the current emphasis on green chemistry and rising awareness of environmental pollution it may be necessary for us to utilize abundantly freely available, non-toxic and environmentally friendly water as the medium to perform photoreactions. Although water has attracted the attention of organic synthetic chemists, it is yet to receive the indispensable attention of photochemists. In this article we present examples of photocycloaddition reactions of four molecules namely coumarin, indene, cinnamic acid and acenaphthylene that are sparingly soluble in water. Photodimerization of these molecules in water is much faster and occurs at much lower concentrations than in organic solvents. Aggregation probably forced by hydrophobic association is suggested to be the cause for the increased reactivity even at lower concentrations. The dimer distribution in water is different from that in organic solvents. Further work is required to fully understand the mechanism of photodimerization in water. Although the poor solubility of organic molecules in water requires one to irradiate large volumes to collect enough useful amounts, availability of flow reactors and LEDs as light sources should help one overcome the challenges.
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- Award ID(s):
- 1807729
- PAR ID:
- 10283743
- Date Published:
- Journal Name:
- Journal of photochemistry
- ISSN:
- 0047-2670
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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