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.
In this paper, the circularly polarised luminescence (CPL) properties of peptides with pyrene in water is described. To consider new ways to control CPL in water, we synthesized a chiral LL‐oligopeptide luminophores with two fluorescent pyrenyl and some hydrophilic arginine units. CPL from a transparent pyrenyl excimer was shown at 480 to 510 nm in water. Their CPL signs can be adjusted by changing the number and position of arginine units at the ends of the chiral peptide backbone. More information can be found in the Communication by Mizuki Kitamatsu, Yoshitane Imai et al.
It is important to optimize the photoexcited-state conformation of chiral luminescent molecules to enhance the intensity of circularly polarized luminescence (CPL) and control the direction of CPL rotation. In pyrenyl peptide luminophores, the intensity and sign of CPL is determined by the solvent and intramolecular distance between pyrenyl units in addition to peptide chirality. However, the control of CPL properties in water is difficult, and new methods to control CPL in water are required. In this study, we achieved amplification and control of the sign of excimer-origin CPL by adding γ-cyclodextrin to a flexible bipyrenyl peptide luminophore with two arginine groups in water.
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