No abstract

The CPL sign is controllable by varying the number of naphthalene units and peptide/Eu(iii) coordination ratio.

Chiral organic and organometallic luminophores that possess circularly polarized luminescence (CPL) properties in the near-ultraviolet to near-infrared region have several useful applications. However, the CPL properties are subject to inherent factors of the compounds; to date, studies on the CPL properties influenced by amino acids and peptides are scarce. Consequently, we developed peptide-pyrene organic luminophores exhibiting various CPL properties. It is conceivable that the peptide-pyrene organic luminophores can be obtained as aggregates when dissolved in a solution. It is also possible that the formation of aggregates makes it difficult to accurately examine the CPL of the peptide in the solution. This study showed that the introduction of sterically hindered 2-aminoisobutyric acid (Aib) units into the peptide backbone inhibits aggregate formation. The resulting luminophores exhibit CPL properties owing to the presence of pyrene units. The results of this study can form a basis for the design of future materials that use peptide-pyrene organic luminophores.

Determining the conformation of a chiral luminescent molecule in its ground state as well as in its photoexcited state is difficult. In the case of a pyrenyl peptide, the sign of its circularly polarised luminescence (CPL) is determined by the solvent or the intramolecular distance between its pyrenyl units; consequently, a new method for controlling CPL in water is required. Herein, we report that chiral LL-oligopeptide luminophores bearing two fluorescent pyrenyl and hydrophilic arginine units exhibit clear excimer-origin circularly polarised luminescence (CPL) at 480-510 nm in aqueous solution. The CPL sign is tuneable by altering the number and positions of the arginine units on the edges of the chiral peptide backbone.