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

Controlling the sign of Excimer‐Origin Circularly Polarised Luminescence by Balancing Hydrophilicity/Hydrophobicity in Bipyrenyl Arginine Peptides

“…[8] LL-1 exhibited strong excimer CPL with a j g CPL j of ~5.3 × 10 À 3 (Figure 1(a); upper). [6] In a similar manner LL-2À LL-4 mainly exhibited strong excimer CPL bands, while weak monomer CPL signals were observed (λ CPL = ~397 nm), as shown in the upper spectra in Figures 1(b)-(d). The j g CPL j values for these excimers were a factor of ~10 À 3 lower than that of LL-1 (Table 1).…”

“…We used the dimensionless Kuhn's anisotropy factor, g CPL , to quantify the chirality of the photoexcited state [8] . LL‐1 exhibited strong excimer CPL with a | g CPL | of ∼5.3×10 −3 (Figure 1(a); upper) [6] . In a similar manner LL‐2−LL‐4 mainly exhibited strong excimer CPL bands, while weak monomer CPL signals were observed ( λ CPL =∼397 nm), as shown in the upper spectra in Figures 1(b)–(d).…”

“…Chiral bipyrenyl arginine oligopeptides LL‐1−LL‐12 were prepared from Fmoc−Arg(Pbf)−OH, Fmoc−Ala(1‐Pyr)−OH, and Fmoc‐Gly−OH, using standard solid‐phase peptide methods (Scheme 1 and SI) [4,6] …”

“…Chiral bipyrenyl arginine oligopeptides LL-1À LL-12 were prepared from FmocÀ Arg(Pbf)À OH, FmocÀ Ala(1-Pyr)À OH, and Fmoc-GlyÀ OH, using standard solid-phase peptide methods (Scheme 1 and SI). [4,6] First, the steady-state unpolarised photoluminescence (PL) and CPL spectra of dilute aqueous LL-1À LL-4 (5.0 × 10 À 5 M) were compared as functions of X and Y to clarify their photoexcited-state properties. Although quenching through aggregation is the most serious problem for a luminophore, [7] LL-1À LL-4 clearly exhibited PL arising from its pyrenyl moieties in water (Figures 1(a)-(d), lower spectra).…”

Excimers in Multichromophoric Assemblies: Boon or Bane?

“…reported an antihelical effect, in handed polymer helix induced a left-handed CPL, An interesting odd-even effect on the handedness of excimer CPL was reported in a series of chiral oligopeptides decorated with a pair of pyrene units. 28 Pyrene units separated by an even number of intervening atoms gave rise to a negative CPL signal, and conversely for an odd number of atoms, the CPL signal turned positive in water. The dependence of the handedness of CPL emission on the arrangement of chromophores in the excimeric state opens up an avenue for the development of stimuli-responsive CPL dyes.…”