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Controlling chromophore chirality in three‐dimensional space is crucial for understanding the structure–chiroptical relationship. Such control enables the prediction of ideal materials for use in chiral photonic applications. In this study, optically active multipyrene systems are synthesized on peptoids. Pyrene‐based chiral submonomers, (S)‐ and (R)‐1‐pyrenylethylamine (s1pye and r1pye), are successfully incorporated into peptoids as the respective (S)‐ and (R)‐N‐(1‐pyrenylethyl)glycine (Ns1pye and Nr1pye) units. NMR spectroscopy revealed length‐ and N‐acetylation‐dependent conformational homogeneity enhancement in solution, stabilizing cis‐amides in Ns1pye‐containing peptoids. The X‐ray crystal structure of Ns1pye tetramer displayed a polyproline type‐I (PPI)‐like helix. All of the pyrene‐related absorptions are circular dichroism (CD) active, and the CD signal related to the long‐axis‐polarized transition increased with helical stabilization. Intramolecular excimer generation yielded significant circularly polarized luminescence (CPL) in the excimer emission region. Early‐stage peptoids emitted left‐handed CPL, but upon acquiring a PPI‐like helix character, CPL handedness became inverted. The CPL dissymmetry factor (glum) was comparable or superior (10−2) to that of chiral organic dyes (10−5–10−2). This new class of helical pyrene‐containing peptoids provides a CPL‐active intramolecular excimer, modulating optical activity through peptoid secondary structure homogeneity. [ABSTRACT FROM AUTHOR]

Despite advances of lanthanide-doped upconversion (UC) materials, the applications such as light-emitting diode and biological imaging are limited by low quantum efficiency. For this context, the understanding of unique interactions between the doped-lanthanides and the host crystals has attracted a huge amount of the researcher's interest. In particular, it was revealed that doping lanthanide ions in a non-centrosymmetric site of host lattice is the cause of relaxation of the Laporte selection rule in the 4f–4f transition of lanthanide ions. One of the layered perovskites CsBiNb2O7 is known to have non-centrosymmetric sites, which would lead to highly bright UC emission. Nevertheless, to our knowledge, there has been no research on the UC comparison between host materials of CsBiNb2O7 with other hosts. In this article, we present the UC intensity comparison of Yb3+–Er3+ ion doped CsBiNb2O7, NaYF4, BaTiO3, and SrTiO3 hosts (the UC in CsBiNb2O7:Er3+,Yb3+ was 2.4 times that of NaYF4:Er3+,Yb3+ and ∼70 times that of SrTiO3:Er3+,Yb3+). After that, we dig into UC, downshifting, and double beam system UC properties. The activator concentration was optimized by varying the doping ratio of Yb3+ and Er3+, and we found out the main reason for the concentration quenching behavior in Er3+ ion doped CsBiNb2O7 is dipole–dipole interaction. In addition, the double excitation experiment indicates that the absorption (4I15/2 → 4I13/2) factor is stronger than the stimulated emission (4I13/2 → 4I15/2) factor in CsBiNb2O7 under 1540 nm laser irradiation. [ABSTRACT FROM AUTHOR]

Most photophysical studies in the halide perovskite have focused on the characteristics of the surface. However, the photons generated at the surface would be absorbed by the same material (re-absorption), and the photophysics of re-absorbed photons are rarely studied. Herein, we present our recent observation of the re-emission (photoluminescence after re-absorption, IR) in Cs4PbBr6, which is temporally slower than the surface-emission (IS). We performed a characterization of Cs4PbBr6, a power dependence experiment, and a lifetime measurement to reveal the emitting properties of Cs4PbBr6. However, we characterized the first re-emission (re-emission after first re-absorption, IFR) of Cs4PbBr6. The analysis of IFR revealed that the energy intervals between IS and IFR and between IFR and final re-emission (IR) are close to integer multiples. Therefore, we suggested that the least number of repeated re-absorptions required for generating IR is three. [ABSTRACT FROM AUTHOR]