Equilibrium acetonitrile titration for (a) intramolecular FRET and (b) intermolecular FRET. (a) 2_FQ, 3_FQ, 1_FQ, and 10_FQ were titrated with acetonitrile in the absence and presence of 10 mol equiv of ZnCl2. The fluorescence intensities from reference molecules (2_F, 3_F, and 1_F) were also measured in order to obtain the intramolecular FRET efficiency as described in Figure 2. (b) 2_F + 2_Q and 3_F + 3_Q were titrated with acetonitrile in the absence and presence of 10 mol equiv of ZnCl2. The fluorescence intensities from reference molecules (2_F + 2 and 3_F + 3) were also measured in order to obtain the intermolecular FRET efficiency as described in Figure 2. Tris-HCl (5 mM, pH 7.5) was used for the buffer. The concentrations of each individual peptoid for intra- and intermolecular FRET are 2 μM and 1 μM, respectively.