Maximized circularly polarized luminescence from metal clusters accelerates chiral photopolymerization

Abstract

The practical application of the circularly polarized luminescence (CPL) emitted from chiral substances faces significant hurdles, primarily due to the small luminescence dissymmetry factor (g_lum) and low photoluminescence quantum yield (PLQY). Herein, we demonstrate a hierarchical system in which metal clusters exhibit excellent CPL performance, with both excellent g_lum factors and high PLQYs, thereby triggering enantioselective photopolymerization. Their CPL activities are sequentially amplified in different assembly forms induced by liquid crystals (LCs), and the maximum g_lum factor is increased by 1240 times, reaching a value of 1.24. The PLQYs of the metal clusters in different assembled states are sharply enhanced compared to that in the discrete state. Benefiting from the CPL performance of the metal clusters, their CPL was used to remotely regulate enantioselective polymerization, thus realizing light-to-matter chirality transfer. Impressively, upon incorporation of achiral luminophores, the polymer system is endowed with CPL through sequential chirality transfer. These innovative achievements open new avenues for the design and cutting-edge application of CPL-active metal clusters.

Fig. 1. Illustration of improvement of the optical activity from atomically precise metal clusters.

A Design concept based on strong interactions between the CPL in metal clusters and CLCs. B Experimental methods (stages II, III, and IV) for improving the CPL performance. C Comparisons of g_lum factors and PLQYs between this work (stages II, III, and IV) and other reported coinage metal clusters. Inset, SCLC device in stage IV under NL and UV irradiation. NL, natural light; UV, ultraviolet.

Fig. 2. Structure and optical analysis of enantiomeric silver clusters (stage I).

A Synthetic illustration of the desired Ag₆ clusters. Colour codes: S, orange; Ag, blue; N, blue; and C, grey. H atoms are omitted for clarity. B Positive mode ESI‒MS spectra of S-Ag₆ dissolved in DMF. Insets: Enlarged portion of the ESI‒MS exhibiting the measured (green line) and simulated (red line) isotopic distribution patterns in the m/z range of 1100–2500 with a charge state of + 1. The dominant peak for S-Ag₆ can be assigned to [S-Ag₆(S₂C₆H₁₀N)₅]⁺ (m/z = 1448.6220). C Normalised absorption and emission spectra of S-Ag₆ (λ_ex = 370 nm) in DCM solution. (Inset: image of S-Ag₆ under UV light in DCM at room temperature). D PXRD patterns of simulated and as-prepared crystals of S-Ag₆. E CD spectra of (S/R)-Ag₆ in DCM solution. F CPL spectra of (S/R)-Ag₆ in DCM solution (λ_ex = 370 nm). G g_lum curves of (S/R)-Ag₆ in DCM solution.

Fig. 3. Chiroptical properties of (S/R)-Ag₆ in stage II.

A Schematic illustration of the formation of the LC assemblies. B Normalised excitation and emission spectra of R-Ag₆-based LC assemblies. C CD spectra of the LC assemblies showing mirror-image signals. The weight ratio of (R/S)-Ag₆/SLC1717 was 1 wt%. D CPL spectra of the LC assemblies. The weight ratio of (R/S)-Ag₆/SLC1717 was 1 wt%, and the excitation wavelength was 370 nm.

Fig. 4. Chiroptical properties of (S/R)-Ag₆ in stage III.

A Reflection spectra of R811/SLC1717 at different weight ratios from 20 wt% to 32 wt%. Inset: Corresponding images under NL. B CD spectra of S811/SLC1717 and R811/SLC1717 at different weight ratios from 20 wt% to 32 wt%. C Schematic illustration of the formation of the ternary G-CLCs. D CD spectra of the ternary-component G-CLCs. E Change in the CD intensity from S811/SLC1717 to the ternary-component CLC assemblies. F Schematic illustration of the deformation of the helical arrangement after the introduction of (S/R)-Ag₆. G Overlap of the reflection spectra and PL spectra of R-Ag₆. H CPL spectra of the ternary G-CLCs (R-Ag₆/R811/SLC1717 and R-Ag₆/S811/SLC1717); the excitation wavelength is 370 nm. I CPL spectra of the ternary G-CLCs (S-Ag₆/R811/SLC1717 and S-Ag₆/S811/SLC1717); the excitation wavelength is 370 nm. J Schematic illustration of the chiral amplification principle in the systems, i.e., the sergeants-and-soldiers rule. Sergeant 1, (S/R)-Ag₆; sergeant 2, R811/S811; solider, nematic LC. K Illustration of an enantioselective effect in the ternary assemblies (both sergeants 1 and 2).

Fig. 5. CPL behaviour of (S/R)-Ag₆ in stage IV.

A Schematic fabrication of the SCLC devices used in this work. B Illustration of the purified CPL activity of silver clusters in the SCLC device. The excitation light first excited an SCLC device, and the CPL from silver clusters entered the detector. C CPL spectra of the SCLC devices (λ_ex = 370 nm). D g_lum curves of the SCLC devices. E Luminescent images of the SCLC devices, which were captured without a circular polariser (left column) and through a right-handed circular polariser (middle column), and a left-handed circular polariser (right column).

Fig. 6. Enantioselective photopolymerization.

A Schematic representation of the experimental setup for the photoinduced polymerisation of DPAMOC. B Schematic illustration of the production of an optically active polymer from racemic monomers (DPAMOC) through the asymmetric thiol–ene polymerisation process triggered by the yellow CPL from silver clusters and UV irradiation at 365 nm. C C D spectra of the resultant chiral polymers prepared by photopolymerization triggered by CPL and normal UV light. Chirality transfer from CPL to the chiral polymer. D FTIR spectra of the resulting linear polymer and polymer monomer. E CD spectra of the resulting host‒guest systems prepared by photopolymerization with the addition of the dye molecule R6G. Chirality transfer from CPL to the chiral polymer to R6G. F Normalised excitation and emission spectra of the chiral polymer‒R6G host‒guest system. G CPL spectra of the resulting host‒guest systems (chiral polymer and R6G).