Biomimetic non-classical crystallization induced hierarchically structured ecient circularly polarized phosphors

Hierarchically structured chiral luminescent materials hold promise for achieving ecient circularly polarized luminescence. However, a feasible chemical route to fabricate hierarchically structured chiral luminescent polycrystals is still elusive because of their complex structures and complicated formation process. We here report a biomimetic non-classical crystallization (BNCC) strategy for preparing ecient hierarchically structured chiral luminescent polycrystals using well-designed highly luminescent homochiral copper(I)-iodide hybrid clusters as basic units for biomimetic crystallization. By monitoring the crystallization process, we unravel the BNCC mechanism, which involves crystal nucleation, nanoparticles aggregation, oriented attachment, and mesoscopic transformation processes. We nally obtain the circularly polarized phosphors with both high luminescent eciency (32%) and high luminescent dissymmetry factor (1.5 × 10 -2 ), achieving the rst demonstration of a circularly polarized phosphor converted light emitting diode with a polarization degree of 1.84% at room temperature. Our designed BNCC strategy provides a simple, reliable and large-scale synthetic route for preparing bright circularly polarized phosphors. absorption Powder X-ray diffraction

g lum = 2 × I L -I R I L + I R (1) where I L and I R are intensities of left-and right-handed circularly polarized emissions. The maximum value of g lum is ±2, which implies the ideal left-or right-handed circularly polarized luminescence.
However, because of the inter-restriction of magnetic dipole transition and electric dipole transition, traditional CPL-active materials, such as chiral luminescent organic molecules and coordination compounds, are di cult to obtain both high photoluminescence e ciency and large g lum values. 6,7 The hierarchical con guration of chiroptical units are promising to enhance CPL performance via the novel structural chirality ampli cation through multiscale levels. 8,9 However, the well-developed hierarchical construction of chiral unit assemblies for e cient CPL is still lack on account of the structural diversity and multi-size dispersity of the conventional chiral units. 10 In addition, understanding the mechanism of structure-function relationship of chiral unit assemblies is highly dependent on the structure of basic chiral units. Therefore, an advanced strategy to conduct hierarchically structured assemblies of well-de ned chiral luminescent units across multiscale levels towards e cient CPL is urgently desirable. 8, 11,12 In natural biomaterials, hierarchical structures regulated by chiral molecules across multiple scale for chirality ampli cation is considerably ubiquitous. As the building blocks of lives on the earth, chiral sugars and amino acids endow the biomacromolecules such as nucleic acids and proteins with stable helical structures. 13 These macromolecules like proteins serve as organic matrix, which induce and regulate the stereoselective non-classical crystallization of calcium carbonate at room temperature to form the macroscale chiral-shaped biominerals, 14,15 e.g., helical textures on seashells. 16 This implies that the hierarchically structured chiral polycrystals can be synthesized for chirality ampli cation through a feasible biomimetic non-classical crystallization (BNCC) process at room temperature based on the wellde ned homochiral units. 17 Nevertheless, using the mild BNCC strategy to construct arti cial hierarchically structured polycrystals with high performance CPL has never been achieved due to the absence of homochiral luminescent units.
An appropriate homochiral unit to construct hierarchical CPL-active assemblies via BNCC should be structurally robust and highly luminescent. Here, we turn our attention to copper(I)-iodide (Cu-I) hybrid clusters owing to their highly luminescent e ciency characteristics, as well as structural identity and robustness for the rational design of homochiral units. [18][19][20][21][22][23][24] We consider that the chiral Cu-I hybrid clusters are potential homochiral units to fabricate hierarchically structured CPL-active materials through the feasible and mild BNCC route.
Herein, we report a BNCC route to synthesize hierarchical structure induced chirality ampli ed CPL-active materials as e cient circularly polarized phosphors endowing light emitting diodes (LEDs) bright circularly polarized emissions. Our strategy is featured by the multiscale design and assembly process that mimicking the formation of chiral biominerals. We design and synthesize a series of chiral Cu-I hybrid clusters as highly luminescent homochiral units. Thereafter, to amplify the chirality for e cient CPL, we conduct the assemblies of Cu-I hybrid clusters at nano-and micro-scales to yield hierarchically structured CPL polycrystals via the BNCC. Compared to directly precipitated powders without hierarchical chiral structures, our hierarchical assemblies of chiral Cu-I hybrid clusters exhibit much higher g lum value of 1.5 × 10 −2 , as well as maintaining high photoluminescence quantum yield (32%). Using obtained polycrystals as phosphors, for the rst time, we present a CPL-active light emitting diode device with a polarization degree of 1.84% at room temperature.

Results And Discussion
Homochiral luminescent cluster design and synthesis. Aiming to the rational design of reliable basic units, we select chiral modi ed triethylenediamine (ted) as chiral ligands to construct robust and luminescent homochiral Cu-I hybrid clusters for the rst time. Synthetic procedures of these four chiral ligands are described in Fig. 1a. To study the effects of chiral center position and chain length of ligands on the BNCC assembly, four chiral ligands with different alkyl chain lengths and chiral center positions are designed (Fig. 1b, left column). Four different chiral iodohydrocarbons are synthesized from corresponding chiral alcohol molecules by nucleophilic substitution (detail phase see Methods). 25 Then, such chiral alkyl chains are introduced into ted to form chiral quaternary ammonium salts, which serve as ligands combined with Cu-I inorganic modules by means of all-in-one typed coordinate bonds and ionic bonds together to construct chiral hybrid clusters. 22 All the synthetic organic compounds can be con rmed by 1 Fig. 1-8).

H NMR analysis (Supplementary
As shown by uorescence microscopy images ( Supplementary Fig. 9), high quality single crystals of chiral clusters were obtained by the slow diffusion method. 22,23,26 All chiral cluster structures in the obtained single crystals can be determined by single-crystal X-ray diffraction (SCXRD). As shown in middle column of Fig. 1b, the obtained chiral clusters from L 2 to L 4 have the same Cu-I nucleus, and the corresponding formulas can be illustrated as Cu 5 I 7 (L 2 ) 2 , Cu 5 I 7 (L 3 ) 2 and Cu 5 I 7 (L 4 ) 2 , respectively.
Differently, the crystal obtained by L 1 is constructed by Cu 4 I 4 (L 1 ) 4 4+ as cationic clusters and one  Fig. 11-14). Additionally, circularly dichroism (CD) signals of these isotropic powders measured by diffuse re ectance are clearly distinct ( Supplementary  Fig. 15), implying that the chirality were successfully introduced into novel Cu-I hybrid clusters on the molecular scale.
Optical properties of chiral cluster based single crystal powders. To explore optical properties of the synthesized Cu-I hybrid chiral clusters, a series of characterizations on these synthesized single crystal powders were carried out. Fig. 2a shows steady photoluminescent (PL) spectra and UV-vis absorption spectra of these crystal powders. The PL peaks of four crystal powders shift from green (540 nm) to orange red (650 nm) with the chiral ligand employed from L 1 to L 4 . Alkyl chain lengths show an obvious in uence on the luminescent e ciency as that PLQYs increase with shortening the chain length (50%, 65%, 10%, 7% for Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− , Cu 5 I 7 (L 2 ) 2 , Cu 5 I 7 (L 3 ) 2 , Cu 5 I 7 (L 4 ) 2 , respectively). It is probably because the shorter alkyl chains have less rotations and wiggles in the crystal lattice to enhance the aggregation induced light emission. 27,28 UV-vis absorption spectra show that all these clusters have strong absorptions of light at the wavelength lower than 400 nm, implying their potentials as e cient phosphors due to large Stokes shifts induced weak self-absorption. Thermogravimetric analyses (TGA) further indicate that the obtained hybrid clusters have excellent thermal stabilities with average thermal decomposition temperatures higher than 200°C (Fig. 2b). In addition, PL lifetimes decay curves of Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− and Cu 5 I 7 (L 2 ) 2 show best t with single ( rst-order) exponential decay functions ( Fig. 2c), and the PL lifetime decay constant (τ) is 7.2 and 3.4 µs respectively, identifying that their emission behaviors belong to phosphorescence (Fig. 2d). In addition, these isotropic crystal powders behave CPL, but their g lum values were still low on the order of 10 −4 magnitude ( Supplementary Fig. 16).
BNCC of hierarchically organized chiral polycrystals. As shown in above results, CD and CPL signals of single crystal powders are relatively weak. Aiming to largely improve chiroptical properties, we attempt to magnify the chirality of the well-designed chiral clusters via the BNCC induced hierarchically structural assemblies (Fig. 3a). We rst used polyvinyl pyrrolidone (PVP, K88-96), a kind of amphiphilic polymer, to con ne Cu-I ionic chains in the micelle, which formed a homogeneous colloidal solution according to our previous work. 29 Then, the synthesized chiral ligands were added into the colloidal solution system, in which the coordinative and electrostatic interactions make these primary liquid precursors combine together to form the designed chiral clusters. Under the regulation of PVP and excess chiral ligands, the aggregation of chiral clusters gradually transformed into hierarchically structured polycrystals through the BNCC process.
We monitored the crystallization process of Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− and Cu 5 I 7 (L 3 ) 2 hierarchical polycrystals at different crystal formation state by scanning electron microscopy (SEM). Impressively, the crystallization process can be well described by BNCC, which is classi ed in the following four stages. Waals forces can further induce these aggregated nanoparticles to arrange with a speci c orientation. At this stage, excess chiral ligands, regarded as a kind of amphipathic surfactants, were partially and dynamically absorbed on the nanoparticle surfaces to "code" their alignment. 30 More importantly, excess chiral ligands in the colloidal solution created a chiral microenvironment, inducing the helical oriented attachment of nanoparticles and spontaneously forming highly ordered mesocrystals with primary helical morphology ( Fig. 3d and Fig. 3h). (4) Mesoscopic transformation into polycrystals: at this stage, mesocrystals have already exhibited crystallographic register because of highly ordered arrangement of nanoparticles. However, they behave transient features due to the high driving force of the fusion of crystal boundaries. 30 To be speci c, although nanoparticles align to each other with high orientation, some gaps are still preserved among them. Enough rotational freedom was still existed so that particles can rotate and wiggle to correct positions. 31 At one certain point, crystal faces are driven to mutually align and fuse by large thermodynamic driving force. 32,33 Eventually, mesocrystals evolved to the nal hierarchically organized chiral polycrystals with high thermodynamic stability ( Fig. 3e and Fig. 3i).
We further con rm the driving forces of chiral crystallization through the high resolution transmission electron microscopy (HRTEM). As shown in Fig. 3j, the lattice fringe spacing is 3.7 Å and 7.8 Å, corresponding to the interplanar spacing (600) and (220) planes of the assembled Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− polycrystals, respectively. Meanwhile, a selected area electron diffraction (SAED) pattern shows the electron diffraction spots of (400) and (440) planes (inset in Fig. 3j). These results reveal that the exposed crystal planes in the obtained polycystals is the (002) plane dominantly, which further indicates that the helical arrangements of assembly units depend on a speci c steric con guration caused by the Van der Waals forces among chiral ligands extended out of the (002) planes between two surfaces of the assembly units of Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− polycrystals (Fig. 3k).
Similarly, such BNCC process can be also observed in the formation of Cu 5 I 7 (L 2 ) 2 polycrystals (Supplementary Fig. 17b) with drop-shaped micromorphology ( Supplementary Fig. 18a-d). Nonetheless, hierarchical crystallization process of Cu 5 I 7 (L 4 ) 2 is unique in comparison to other three polycrystals, which went through microstructures of conglobate particles, nanosheets and helical nanobelts, respectively (see Supplementary text 1).
The crystallization monitoring also revealed that different crystallization rate induced by ligands correspondingly in uenced hierarchical features of the obtained polycrystals. The short alkyl chain ligands would lead to more rapid formation of nanoparticles than that for ligands with long chains. To be speci c, PXRD patterns indicated that the crystalline phases of Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− and Cu 5 I 7 (L 2 ) 2 have already formed at 20 and 3 minutes, respectively. In contrast, the crystalline phase of Cu 5 I 7 (L 3 ) 2 did not form entirely in the initial reaction of 2 hours. For Cu 5 I 7 (L 4 ) 2 , the nal nanobelts need longer time (7 ~ 12 hours) to crystallize (Supplementary Fig. 17d and 18g, h). These are the fact that short alkyl chains absorbed on the assembly units lead to less repulsive forces than long alkyl chains ( Supplementary Fig.  20). For the same reason, ligands with short terminal chains, such as L 1 and L 2 , tend to induce assembly units to arrange more compactly ( Fig. 3e and Supplementary Fig. 18d). Oppositely, L 3 and L 4 prefer to induce assembly in a sparser way derive from the relative independence of assembly units ( Fig. 3i and Supplementary Fig. 18h).
Hierarchical structure ampli ed chiroptical properties of polycrystals. We measured the solid state CD spectra of the obtained polycrystals via diffuse re ectance method to compare with that of single crystal powders without hierarchical structure features (Supplementary Fig. 15 and Supplementary Fig. 21). The results suggested that CD signals displayed an order of magnitude improvement by this BNCC process, demonstrating the effective magni cation of chirality via the hierarchical organization of chiral clusters. In addition, we prepared polycrystals based on the racemic L 1 ligands through the same BNCC process.
The obtained polycrystals present bundle structures that consisted of gathered parallel nanorods ( Supplementary Fig. 22a) rather than helical structures of polycrystals induced by homochiral ligands. No corresponding CD and CPL signals were obtained for these racemic polycrystals ( Supplementary Fig.  22b-d), which con rmed that the chirality of hierarchical polycrystals is indeed derived from homochiral hybrid clusters, implying the importance of homochiral clusters for stereoselectivity of hierarchical crystallization.
To further amplify the chirality by structural regulation, we explored the relationship between hierarchical features and chiroptical properties through changing the concentration of chiral ligands in the reaction solutions. The polycrystals obtained at different concentration of ligands are all crystalline phases ( Supplementary Fig. 23). Fig. 4a-p and Supplementary Fig. 24a-p provide SEM images with high and low magni cation, respectively. For Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− , when the concentration of L 1 is low, the obtained polycrystals are rod-like morphology ( Fig. 4a and Supplementary Fig. 24a), showing weak signals of CD (80 mdeg) and CPL (g lum = 9.6 × 10 −3 ) (Supplementary Fig. 25). With the increase of the concentration of L 1 , excess chiral ligands absorbed on nanoparticle surfaces and existed in the solution make nanoparticles favor to attach mutually and twist via helical pattern, forming the hierarchically structured chiral polycrystals (Fig. 4b and Supplementary Fig. 24b). The helical degree is maximum when the concentration of L 1 reaches to 6 mM ( Fig. 4c and Supplementary Fig. 24c). Simultaneously, at this concentration, chiroptical properties of the obtained polycrystals are strongest correspondingly. CD spectrum shows a positive Cotton effect and the CD signal reaches to 260 mdeg. The CPL signal is also strongest with the highest g lum value of 1.5 × 10 −2 ( Supplementary Fig. 25). However, a greater amount of L 1 did not lead to the stronger chiral bias. On the contrary, when concentration of L 1 is higher than 7 mM, weaker CD signals and CPL emissions are observed. This is understandable because reaction rate is accelerated with the increase of the L 1 concentration so that the crystallization is completed more rapidly than the process of chiral regulation. Thus, a plenty of monomer particles aggregated more closely and attempted to form radially oriented nanorods converging to the center point without chiral structural features ( Fig. 4d and Supplementary Fig. 24d).
For Cu 5 I 7 (L 2 ) 2 polycrystals, the bent garlic clove-liked shapes were observed when the concentration of L 2 is low ( Fig. 4e and Supplementary Fig. 24e). This bent hierarchical structures do not exhibit strong CD and CPL due to their bent directions are random when they are dispersed in solvent, leading to the same contribution of left-handed and right-handed CD or CPL signals ( Supplementary Fig. 26). As the concentration of L 2 increased, the degree of bending reduced and polycrystals tended to display dropliked shapes (Fig. 4f, g and Supplementary Fig. 24f, g). Meanwhile, CD spectra showed positive Cotton effects and these drop-liked polycrystals exhibited the strongest CD and CPL with a g lum value of 4.0 × 10 −3 (Supplementary Fig. 26). When the concentration of L 2 increased to 30 mM, nanoparticles aggregated into glomerate structures, assimilating with that of Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− (Fig. 4h and Supplementary Fig. 24h), which presented weak CD and CPL ( Supplementary Fig. 26).
We found that helical structures always existed regardless of the concentration of L 3 . When the concentration of L 3 was low, plenty of lamellar units twined densely and terminals of unit stretched out of the side so that the chiral scattering on helical structure is not very obvious ( Fig. 4i and Supplementary  Fig. 24i), resulting in the relatively weak CD and CPL (Supplementary Fig. 27). However, the higher concentration of L 3 caused sparser units to twine together (Fig. 4j, k and Supplementary Fig. 24j, k), which is because the higher dense of ligands on surfaces of lamellar units induced the helical assembly. Furthermore, with the increase of the concentration of L 3 , the helicity of polycrystals became stronger and then prolonged ( Fig. 4l and Supplementary Fig. 24l). As a consequence, the variation tendency of CD and CPL are much the same as that of helicity change of hierarchical structures, both of which are enhanced with the increase of the concentration of L 3 (Supplementary Fig. 27).
With respect to Cu 5 I 7 (L 4 ) 2 polycrystals, as the concentration of L 4 increased, the variation tendency of hierarchical structures was similar to the structure change with the prolongation of the reaction time, which experienced through the conglobate particles, nanosheets and helical nanobelts (Fig. 4m-p,  Supplementary Fig. 24m-p). The chiroptical properties of these polycrystals is not strictly related to the microstructure variation because of their different crystal phases. The nanosheets with no helical structures can yield stronger CPL with a g lum value of 6.0 ×10 −3 and weaker CD than helical nanobelts ( Supplementary Fig. 28).
Circularly polarized phosphor performance for the application in LED device. As a result of our above exploratory experiments on the regulation of ligand variety and concentration, we state that these two factors both play important roles in obtaining outstanding CPL-active polycrystals. As shown in Fig. 5a, on the one hand, ligands with long alkyl chains at molecular terminals, such as L 3 and L 4 , may cause low luminescent e ciency (PLQYs ~ 7% and 6%), owing to the irregular vibration of alkyl chains in crystal lattices render the energy dissipation as heat. On the other hand, despite short alkyl chains contribute a lot on PLQYs (50% for Cu 5 I 7 (L 2 ) 2 ), they may probably lead to weak chiral induction of ligands in the BNCC and then impede the formation of hierarchical structures without obvious chiral features (Fig. 4e-h). Additionally, positions of chiral center are away from terminals of alkyl chain, such as L 2 and L 3 , which may adversely impact on chiroptical properties owing to the inadequate interactions among chiral groups in the hierarchically structured polycrystals. As shown in Fig. 5b Table   2).
These hierarchically structured chiral polycrystals present similar thermal stabilities to single crystals with the average thermal decomposition temperature higher than 200°C (Supplementary Fig. 29), implying that they are suitable as phosphors for LED coating. To validate the feasibility of chiral polycrystals application in circularly polarized LED, we dispersed Cu 4 I 4 (L 1 ) 4 4+ Cu 8 I 12 4− polycrystals in the dichloromethane (CH 2 Cl 2 ) solution of polymethyl methacrylate (PMMA) and coated them on the LED lamp. A uniform composite lm of PMMA/chiral polycrystals was formed after solidi cation when CH 2 Cl 2 evaporated. As shown in Fig. 5e, the fabricated LED device successfully realized bright green light emission with the chromaticity coordinate at (0.350, 0.571). We measured the circularly polarized light emitted by the fabricated LED device (details in Supplementary Fig. 30). There is a marked difference between the left-and right-handed light emission intensities, revealing the obvious circularly polarized light emitted by the fabricated LED device (Fig. 5f). The polarized degree (P) was calculated by P = I L -I R I L + I R × 100% (2) Where I L and I R are emission intensities of left-and right-handed components of the circularly polarized LED device, respectively. The LED device exhibited polarization degree of 1.84% in the wavelength range of 500 to 600 nm at room temperature (Fig. 5g), which is the rst demonstration of bright circularly polarized phosphor converted LED. In contrast, the LED device coated with racemic polycrystals did not exhibit any circularly polarized light emission ( Supplementary Fig. 31).

Conclusion
In summary, we proposed BNCC strategy to synthesized a series of hierarchically structured polycrystals with e cient CPL on the basis of rationally designed chiral clusters. We demonstrate that the obtained polycrystals can realize the magni cation of chirality via the multiscale levels from molecular to nanoand then to mesoscopic scale. Furthermore, we unravel the non-classical crystallization of chiral clusters -mimicking biomineralization eld -to demonstrate the formation process of these polycrystals that can be expanded to other chiral luminescent material systems. Eventually, a LED device with circularly polarized light emission of a polarization degree of 1.84% at room temperature was demonstrated for the rst time, which provides a new strategy to fabricate an e cient circularly polarized lightsource. Preparation of (S)-1-iodo-2-methylbutane. Iodine (3.8 g, 15 mmols, 1.5 equiv.) was added into a solution of triphenylphosphine (3.93 g, 15 mmols, 1.5 equiv.) in CH 2 Cl 2 (100mL) at room temperature. The solution was allowed to stir for 10 minutes. Imidazole (1.7 g, 25 mmols, 2.5 equiv.) was subsequently added into the mixture above. After 10 minutes, chiral alcohol (S)-2-methylbutan-1-ol (0.88 g, 10 mmols, 1.0 equiv.) was dropped into the solution and the reaction system was stirred for 3 hours. Then, the reaction mixture was quenched by the addition of the saturated aqueous solution of Na 2 S 2 O 3 (50 mL).

Methods
Organic and aqueous layers were separated and the aqueous phase was extracted with CH 2 Cl 2 (3×100 mL). The combined organic layers were dried with Na 2 SO 4 (anhydrous). The mixture was ltered and the ltrate was concentrated to give crude product. The residue was puri ed by silica gel column chromatography with hexane to get the colorless oily product (1.69 g, 85.3% yield).
(S)-1-iodo-2-methylbutane (1.60 g, 8 mmol, 1.0 equiv.) was added dropwise into ethyl acetate (60 mL) containing ted (1.35 g, 12 mmol, 1.5 equiv.) under magnetic stirring. The mixture was allowed to stir at room temperature and white solid precipitated out in one day. After this time, the generated precipitates were collected by centrifuged, washed with ethyl acetate, and dried under vacuum to give the pure product (1.56 g, 62.9% yield). The yield is 89.9%.
Growth of single crystals of chiral hybrid clusters. In a 5 mL vial, CuI (190 mg, 1 mmol) was dissolved in KI saturated solution (2 mL). Acetonitrile (1 mL) was added slowly along the inner wall into the bottom layer. Then, 0.5 M ethanol solution of L 1 (0.8 mL) (2 mL for L 2 -L 4 ) was added slowly along the inner wall in to the vial. Transparent single crystals formed overnight and were collected by ltration.
Synthesis of hierarchically structured polycrystals. In a 30 mL vial, 200 mg of polyvinylpyrrolidone (PVP K88-96) was added into 20 mL of ethanol under vigorous magnetic stirring. After PVP K88-96 was fully dissolved, KI saturated solution (0.4 mL) containing CuI (38 mg, 0.2 mmol) was added into the PVP/ethanol solution above. Then, a certain volume of ligands/ethanol solution (0.5 M) was added in. The mixture was allowed to vigorously stir for 12h and then left standing overnight. The resulting white precipitation was collected by centrifugation at 6000 r/min for 3 min, washed with deionized water and ethanol respectively. The obtained polycrystal powders were dispersed in ethanol for storing.
Circularly polarized phosphor coating on LED lamp. In a 5 mL vial, 1 g of PMMA was dissolved in 2 mL of CH 2       Supplementary Files