Based on the UVevis titration, the binding ability (Ks1⁄43.3 103 M1) of receptor 1 for Cu2þ was determined from BenesieHildebrand equation (Fig. S1), and the detection limit was calculated to be 1.4 105 M using 3s/K59 (Fig. S2). Especially, this Ks value was lower than those (104w105 M1) reported for Cu2þ- binding chemosensors,13,54,58,61 suggesting that 1eCu2þ has a somewhat weak binding ability.