Figure 3

¹H NMR spectra (600 MHz, 6.24 mM, 293 K) of 4 with increasing amount of tetrabutylammonium acetate added in hydrated DMSO-d6 (0.5% v/v). The blue star indicates the signal arising from the urea N-H protons, the green circle the signal arising for the C5 naphthalimide proton and the red triangle the 4-amino NH proton.