Sign inversion of excimer circularly polarized luminescence in water-soluble bipyrenyl oligopeptides through an odd-even effect

Abstract

We prepared eight novel chiral arginine-bipyrenyl oligopeptides with different intramolecular distances between two organic luminophore fluorescent pyrene units and investigated their chiroptical properties in water at ambient temperature. These luminophores are highly soluble in water because of the presence of two arginine units; because they carry two pyrene units, they emit strong excimer circularly polarized luminescence (CPL) in the range of 450–600 nm (|gCPL| ≈ (0.1–0.5) × 10–2). When the number of atoms between the two intramolecular pyrenes units was even, the sign of the CPL signals was negative (−), whereas when the atom number was odd, the sign of the CPL signals was positive (+), even in water.