Solubility of Excited States in Micelles: The Nucleophilic Aromatic Photosubstitution of 3-Nitrophenyl Ethers in Anionic Micellar Solution

Abstract

The alkaline photohydrolysis of a series of n-alkyl 3-nitrophenyl ethers was investigated in aqueous micellar solutions of the anionic detergent sodium dodecyl sulfate (SDS). Although SDS micelles strongly inhibit the OH- mediated photohydrolysis of the hydrophobic n-decyl ether, they have very little effect on the photohydrolysis of the corresponding n-butyl ether and actually increase the quantum yield for photohydrolysis of the ethyl and methyl ethers. This unexpected behavior is shown to be the consequence of a rather large decrease in the micellar solubility of the 3-nitrophenyl ether chromophore upon excitation to the triplet state, coupled with a micellar effect on the decomposition of the intermediate sigma complex. On the basis of recent linear solvation free energy relationship analyses of solute incorporation into SDS micelles, this change in micellar solubility is attributed to an enhancement of the hydrogen bond basicity in the excited triplet state of the 3-nitrophenyl ether chromophore.