A Binaphthyl Macrocycle Exhibiting Circularly Polarized Luminescence: On–off Switch Triggered by Molecular Recognition

A series of D₄-symmetric (S)-1,1'-binaphthyl cyclic tetramers were synthesized. The signs and intensities of circularly polarized luminescence (CPL) of the tetramers depend on the substituents, which were caused by differences of the binaphthyl dihedral angles in the excited state. The chiral dye with hydroxy groups did not exhibit CPL. However, this dye exhibited turned-on CPL upon addition of amino acids such as l-phenylalanine in an enantioselective and positive allosteric manner, and the g_lum value reached +7.3 × 10^-3. The CPL was repeatedly switched on and off by changing temperature. The turn-on CPL was caused by the guest molecules expanding the binaphthyl dihedral angles with multiple hydrogen bonds. (+)-Andersen sulfinate also induced enantioselective turn-on CPL.