Studies of the solvatochromic emission properties of N-aroylurea derivatives II: influence of hydrogen-bonding interactions.

The solvatochromic emission properties of five naphthoylurea derivatives with different substitution patterns at the naphthoylurea functionality were investigated, with a particular focus on the influence of inter- and intramolecular H-bonding interactions. The bathochromic shifts of the emission maxima correlate well with the acceptor number or Catalán's acidity of the solvent (Δλ = 47-86 nm), indicating an excited species with a pronounced negative charge that is stabilized by H-bond donating (HBD) solvents. In media with restricted free volume the formation of the charged species is not favored, because the required conformational change to establish an intramolecular charge transfer (ICT) between the fluorophore and the acylurea substituent is hindered, and the emission mainly originates from the locally excited state.

Studies of the solvatochromic emission properties of N-aroylurea derivatives I: Influence of the substitution pattern.

The influence of the substituent of the N-aroylurea functionality on the solvatochromic properties of this class of compounds was investigated with eight examples. The absorption spectra of these compounds exhibit the characteristic spectroscopic properties of the corresponding arene fragment and are only slightly dependent on the solvent. In contrast, all investigated aroylurea derivatives exhibit a strong solvatochromism with a good linear correlation between the emission energy and the acceptor numbers (AN) of the solvents; that is, the emission maximum shifts bathochromically (Δλ = 50-93 nm) with increasing AN.