A novel type of molecular assembly: aggregates formed by molecules with polar chains in nonpolar solvents

The emission spectra and photodimerization of poly(ethylene glycol) oligomers with a naphthalene group as one terminal of each chain (N−Pn) in nonpolar solvents were investigated. The fluorescence spectra of N−Pn in isopentane at temperatures below −20°C are dominated by excimer emission. The addition of unlabeled poly(ethylene glycol) to the solutions results in a reduction in the excimer emission and an enhancement of monomer emission. Fluorescence depolarization measurements at 77 K suggest the existence of significant energy migration. The glassy solutions show a strong delayed excimer fluorescence and triplet exxcimer phosphorescence. The photoirradiation yields ‘cubane-like’ photodimer of the naphthalene groups with high quantum yield. All these observations indicate the lipophobic interactions push N−Pn chains together to form aggregates.