The molecular structure, absorption, and fluorescence spectra of N, N'-dimethyl-N, N'-di-1- pyrenylurea and N, N'-dimethyl-N, N'-di-2-pyrenylurea have been investigated and compared to the properties of N, N, N'-trimethyl-N'-pyrenylurea model compounds. Di-1- pyrenylurea exists as a mixture of folded (E, E) syn-and anti-rotamers that interconvert via flipping of one of the pyrene rings to an unfolded (E, Z) rotamer geometry. The symmetric ...
