Temperature-, Concentration-, and Solvent-Dependent M / P Helicity Switching of Double-Helical Monometallofoldamers with Inversion of Circularly Polarized Luminescence

Fluorescent double-helical monometallofoldamers Ag-(1)2-PF6 were constructed by the mononuclear complexation of two bipyridine strands 1 featuring two L-shaped dibenzopyrrolo-1,2-a-1,8-naphthyridine units at both ends with a Ag-(I) cation. These monometallofoldamers exhibited double-helical/open conformational switching. (R)-Ag-(1c)2-PF6 with chiral side chains induced a single-handed helix sense and enabled precise control of M/P helicity switching in response to a solvent. This complex also exhibited strong fluorescence and circularly polarized luminescence (CPL) inversion switching upon M/P helicity inversion. For instance, (R)-Ag-(1c)2-PF6 exhibited positive CPL in CH2Cl2 (φF = 0.69, g lum = 1.9 × 10-3) and negative CPL in toluene (φF = 0.79, g lum = -2.0 × 10-3). This double helix also aggregated in polar solvents, which led to CPL inversion switching induced by temperature- and concentration-dependent aggregation.