Fluorescent visualization of the conformational change of aromatic amide or urea induced by N-methylation

The conformational change of amide structure of benzanilide or urea structure of N , N ′-diphenylurea induced by methylation of the secondary nitrogen was visualized by introduction of pyrene moieties on the benzene ring. In contrast to the extended trans-form of secondary amide and urea, which showed monomer fluorescence emission of pyrene, the corresponding N-methylated compounds exist in cis-form, which exhibited excimer emission.