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Anion-responsive sign inversion of circularly polarized luminescence (CPL) was successfully achieved by N

Porphyrin ion pairs, the charge of which is delocalized in core units, form tightly associated structures via i π- i π interactions. 5,10,15-Triphenyl-substituted porphyrin-AuIII complex, which is favorable for forming stacked structures in the form of a stable ion, was synthesized. Ion-pair metathesis based on the HSAB theory enabled combination with porphyrin anions possessing electronic states controlled by electron-donating and electron-withdrawing groups. Transient absorption spectroscopy suggested that the lifetimes of the radical pairs generated by photoinduced electron transfer of the ion pairs could be controlled by a judicious combination of the anions and cations.

Nine nona-coordinated Eu(III) complexes (1-9) studied here have three unsymmetric β-diketonate ligands and one chiral Ph-Pybox ligand, which can produce eight possible coordination isomers, depending on the position of the three unsymmetric β-diketonate ligands. Substituents on the β-diketonate ligands cause a rational structural rearrangement upon crystallization. Substituents with higher polarity, including -CN, -F, -Cl, -Br, -OMe, and -OEt, employ intercomplex hydrogen bonding to generate an association complex through structural rearrangement upon crystallization. Substituents with lower polarity, including -CF3, -SMe, and -Me, cause the most energetically favorable isomer to crystallize directly from solution. These two crystal structures exhibit well-resolved f-f emission lines with characteristic Stark splitting structures. This work revealed that the configuration of the Eu(III) complexes in solution can be determined by systematic comparison of their Stark splitting structures to those obtained from the solid phase using density functional theory (DFT)-based predictions combined with circular dichroism data.

Long-wavelength light penetrates deeply in a variety of substances and can induce selective excitation in condensed phases. Therefore, photofunctional materials that are responsive to long-wavelength light are essential. Ag2S nanocrystals (NCs), which are near-infrared-light (NIR)-responsive materials, have applications as NIR phosphors and photosensitizers. However, the excited-state dynamics of Ag2S NCs combined with aromatic molecules have not been elucidated to date. In this study, we synthesized perylene bisimide-coordinated Ag2S nanocrystals (PBI-Ag2S) and investigated the excited-state dynamics by subpicosecond-to-nanosecond transient absorption spectroscopy. When PBI-Ag2S is excited using a 530 nm light, where the excited-state dynamics of the PBI moiety is mainly probed, PBI radical anions are instantaneously produced by ultrafast hole transfer from PBI to Ag2S NCs. Moreover, PBI radical anions are formed even upon excitation with a 720-nm light, where only Ag2S NCs are selectively excited. This study is important for developing novel organic-inorganic nanohybrid photofunctional materials that utilize low-energy light efficiently for applications in photoredox catalysts, optoelectronic devices, and solar cells.

Nine nona-coordinated Eu(III) complexes (1–9) studied here have three unsymmetric β-diketonate ligands and one chiral Ph-Pybox ligand, which can produce eight possible coordination isomers, depending on the position of the three unsymmetric β-diketonate ligands. Substituents on the β-diketonate ligands cause a rational structural rearrangement upon crystallization. Substituents with higher polarity, including −CN, −F, −Cl, −Br, −OMe, and −OEt, employ intercomplex hydrogen bonding to generate an association complex through structural rearrangement upon crystallization. Substituents with lower polarity, including −CF3, −SMe, and −Me, cause the most energetically favorable isomer to crystallize directly from solution. These two crystal structures exhibit well-resolved f–f emission lines with characteristic Stark splitting structures. This work revealed that the configuration of the Eu(III) complexes in solution can be determined by systematic comparison of their Stark splitting structures to those obtained from the solid phase using density functional theory (DFT)-based predictions combined with circular dichroism data.

Long-range chirality recognition between the two chiral guest ligands can be tuned based on the helix distances (dLn–Ln = 11.5 and 14.0 Å) of bis-diketonate bridged dinuclear lanthanide complexes (2Th and 3Th, respectively) used as mediators. Both 2Th and 3Th form one-dimensional (1D) helical structures upon terminal binding of two chiral guest co-ligands (LR or LS). Long-range chiral self-recognition is achieved in self-assembly of 2Th with LR and LS to preferentially form homochiral assemblies, 2Th-LR·LR and 2Th-LS·LS, whereas there is no direct molecular interaction between the two guest ligands at the terminal edges. X-ray crystal structure analysis and density functional theory studies reveal that long-range chiral recognition is achieved by terminal ligand-to-ligand interactions between the bis-diketonate ligands and chiral guest co-ligands. Conversely, in self-assembly of 3Th with a longer helix length, statistical binding of LR and LS occurs, forming heterochiral (3Th-LR·LS) and homochiral (3Th-LR·LR and 3Th-LS·LS) assemblies in an almost 1 : 1 ratio. When phenyl side arms of the chiral guest co-ligands are replaced by isopropyl groups (L′R and L′S), chiral self-recognition is also achieved in the self-assembly process of 3Th with the longer helix length to generate homochiral (3Th-L′R·L′R and 3Th-L′S·L′S) assemblies as the favored products. Thus, subtle modification of the chiral guests is capable of achieving over 1.4 nm-range chirality recognition., Long-range chirality recognition between the two chiral guest ligands can be tuned based on the helix distances (dLn–Ln = 11.5 and 14.0 Å) of bis-diketonate bridged dinuclear lanthanide complexes (2Th and 3Th, respectively).

This work reports on the structural and photophysical characterization of D4-symmetrical octanuclear circular LnIII helicates, [(R)- or (S)-iPr-Pybox]8(LnIII)8(THP)8 (where Ln = Eu and Tb, THP = trianionic tris-β-diketonate, and iPr-Pybox = chiral bis(4-isopropyl-2-oxazolinyl)pyridine). X-ray crystallographic analysis revealed that the octanuclear circular helicate possesses square antiprism architecture and consists of four [(R)- or (S)-iPr-Pybox]2LnIII2(THP)2 asymmetric units arranged in a closed ring form. Ligand-to-ligand interactions between the THP and the iPr-Pybox ligands have successfully directed formation of enantiopure, homoconfigurational (Δ,Δ,Δ,Δ,Δ,Δ,Δ,Δ)-R and (Λ,Λ,Λ,Λ,Λ,Λ,Λ,Λ)-S isomers. All of the nonacoordinated LnIII ions are identical and exhibit a distorted capped square antiprism (CSAP) geometry. Upon excitation of the ligand absorption band (λ = 360 nm), the circular helicates display characteristic EuIII (red, 5D0 → 7FJ, J = 0-4) or TbIII (green, 5D4 → 7FJ, J = 6-3) core f-f luminescence. The overall emission quantum yields of the circular EuIII and TbIII helicates are 0.145 and 0.0013, respectively, in chloroform. The EuIII and TbIII complexes exhibit remarkable circularly polarized luminescence (CPL) activity at their magnetic dipole transition with observed luminescence dissymmetry factors |glum| of 1.25 (5D0 → 7F1, λ = 592 nm) and 0.25 (5D4 → 7F5, λ = 541 nm), respectively. Exceptional |glum| values of the circular EuIII helicates highlight the visible intensity difference between left and right circularly polarized emissions of R and S isomers in chloroform and PMMA thin film.

We report on the design and synthesis of triscyclometalated iridium (Ir) complexes that contain aryloxy groups at the end of diamino linkers, which exhibit an extraordinarily long-emission lifetime, and were prepared by regioselective substitution reactions of

A homoleptic zinc(II) helicate organized by a pair of achiral dipyrromethene ligands through zinc(II) coordination was synthesized to evaluate the chiroptical properties. This zinc complex showed strong exciton-coupled chiroptical responses from the helical configuration with a large absorption dissymmetry factor |gabs | (up to 0.20). More importantly, intense polarized luminescence in the far-red region (700-850 nm) with a fluorescence quantum yield ΦFL of 0.23 was observed for this helicate with a dissymmetry factor |glum | of 0.022, the largest value among rare-earth- and precious-metal-free small molecules. These unprecedentedly large g values were supported by theoretical calculations.

This work demonstrates a methodology for the evaluation of circularly polarized luminescence of a chiral europium(III) (EuIII) complex species in an ensemble system. The chiral EuIII complex species consists of chiral bis(oxazolinyl)pyridine [(R)- or (S)-iPr-Pybox] and β-diketonate ligands with a pendant nitro group (DK-NO2). The pendant NO2 group in [iPr-Pybox](EuIII)(DK-NO2)3 (monometallic EuIII species) coordinates to the EuIII center of another EuIII complex, giving rise to the generation of a chiral EuIII ensemble consisting of mono-, di-, and the other oligomeric EuIII species, {[iPr-Pybox](EuIII)(DK-NO2)3}n. The luminescence dissymmetry factors (glum) of the chiral EuIII ensemble have been successfully determined by using a commercially available fluorescence spectrophotometer attached with a rotatable λ/4 filter and a fixed linearly polarized plate. This study suggests that the chiral EuIII ensemble in solution displays a large circularly polarized luminescence (|glum| = 0.19) as compared to that of a reference monometallic complex [iPr-Pybox](EuIII)(DK-CN)3 (|glum| = 0.11–13). The larger glum is primarily attributed to the contribution of the dimetallic EuIII species exhibiting a high degree of circular polarization in luminescence (glum2 = 0.27) in the ensemble. Conversely, a large linearly polarized component was observed in luminescence from the chiral EuIII ensemble in the solid state (KBr pellet).

This work demonstrated that the ligand symmetry of europium(III) complexes controls the ratiometric luminescence characteristics of lanthanides. Nona-coordinated europium(III) complexes having unsymmetrical β-diketonate ligands (Cs) exhibit distinctive ratiometric spectral variations in the extremely narrow f–f transition bands over the temperature range from 253 to 323 K. In contrast, no such ratiometric change can be observed in a series of nona-coordinated europium(III) complexes containing symmetrical β-diketonate ligands (C2v). The remarkable difference depending on the ligand symmetry (Csvs. C2v) suggests that the coordination rearrangement of β-diketonate in the complex causes ratiometric spectral variations in extremely narrow f–f transition bands, where two europium(III) complex isomers exist in the solution equilibrium. A self-calibration method using dual iso-emissive points is reported, where self-calibration using the two emission intensities at the iso-emissive points reduces the coefficient of variation in luminescence thermometry.

2021