Enhanced Circularly Polarized Green Luminescence Metrics from New Enantiopure Binary Tris-Pyrazolonate-Tb³⁺ Complexes

Abstract

Achieving superior circularly polarized luminescence brightness (B_CPL) is an important subject and continuous challenge for chiroptical materials. Herein, by applying a binary molecular design for the synthesis of chiral organo-Tb³⁺ molecules, a novel pair of mononuclear chiral tris-pyrazolate-Tb³⁺ enantiomers, [Tb(PMIP)₃(R,R-Ph-PyBox)] (2) and [Tb(PMIP)₃(S,S-Ph-PyBox)] (5), have been synthesized and characterized. The three 1-phenyl-3-methyl-4-(isobutyryl)-5-pyrazolone (HPMIP) ligands play the role of efficient luminescence sensitizers and strong light-harvesting antennas, while the enantiopure 2,6-bis(4-phenyl-2-oxazolin-2-yl) pyridine ligand (R,R/S,S-Ph-PyBox) is employed as the strong point-chiral inducer. With the proper combination of the HPMIP and Chiral-Ph-PyBox within the Tb³⁺ enantiomers, strong (PMIP)⁻-centered π-π^* electronic absorption (ε_{263 nm} = 38,400–39,500 M⁻¹ cm⁻¹) and brilliant high-purity ligand-sensitized Tb³⁺-centered green luminescence (Φ_PL = 47–48%) were observed. In addition, a clear circularly polarized luminescence (CPL) activity (|g_lum| = 0.096–0.103) was also observed, resulting in a strong B_CPL (610–623 M⁻¹ cm⁻¹) for the two Tb³⁺ enantiomers from the hypersensitive transitions. Our results offer an effective path to develop high-performance chiroptical organo-Tb³⁺ luminophores.

1. Introduction

Circularly polarized luminescence (CPL) refers to a chiroptical phenomenon in which excited chiral luminophores emit left- or right-circularly polarized emissions after excitation with unpolarized light at a specific wavelength [1]. The chiroptical property is of particular interest owing to its fascinating potential applications in advanced anti-counterfeiting inks [2], enhanced information encryption [3], as well as high-resolution circularly polarized OLEDs (CP-OLEDs) [4]. The comprehensive CPL properties are normally characterized by the CPL brightness (B_CPL; see Equation (1)) [5], and an ideal chiroptical luminophore should maximize four metrics as much as possible: the dissymmetry factor (g_lum), overall luminescent quantum efficiency (Φ_PL), molar extinction coefficients (ε_λ) at the excitation wavelength, and branching ratio (β_i; 0 ≤ β_i ≤ 1) of the considered emission peak. These metrics do not correlate, as they are governed by different selection rules [6]. Hence, it becomes a challenge to achieve a superior B_CPL value by maximizing all parameters for a specific CPL-active system.

$$B_{\mathrm{C}\mathrm{P}\mathrm{L}}={\beta }_{\mathrm{i}}\times {\epsilon }_{\mathsf{\lambda }}\times {\Phi }_{\mathrm{P}\mathrm{L}}\times {\displaystyle \frac{\left|g_{\mathrm{l}\mathrm{u}\mathrm{m}}\right|}{2}}$$

(1)

An effective strategy to overcome this problem is to design chiral heteroleptic binary metal (transition/lanthanide) complexes [6,7,8], where two types of ligands with different functions can facilitate the synergistic optimization of each key metric simultaneously. The former often suffers from a relatively low degree of polarization (10⁻³ ≥ |g_lum| ≥ 10⁻⁵) due to the inherent strong electric dipole (ED) transition moment with a weak magnetic dipole (MD) transition moment [9]. In contrast, significant CPL activity (|g_lum| ≥ 10⁻²) can be observed in the latter with an allowed MD but forbidden ED character from the [Xe]4f⁶/4f⁸ electronic structure of most trivalent lanthanide ions (Ln³⁺ = Eu³⁺, Tb³⁺, Sm³⁺ and Dy³⁺, etc.) [10]. Meanwhile, the Ln³⁺-characteristic radiative transitions and light absorption capacity can be improved by the involvement of both singlet and triplet excitations simultaneously with a controllable antenna effect through the sensitizing ligands [11,12], achieving high Φ_PL and ε_λ values. Eu³⁺/Tb³⁺-based systems are regarded as some of the best candidates for achieving a large B_CPL value for circularly polarized monochromatic red/green luminescence due to their high intrinsic quantum efficiencies (Φ_Ln) [13]. A number of successful examples of CPL-active heteroleptic binary Eu³⁺-centered red-light complexes have been reported in recent years, in which relatively high B_CPL values (103.7–161.73 M⁻¹ cm⁻¹) at ⁵D₀→⁷F₁ transitions were obtained through the coupling of point-chiral N^N/N^N^N-donor ligands to the well-developed chromophoric [Eu(β-diketonate)₃(H₂O)_x] systems [14,15,16,17]. However, despite the concerted efforts in the synthesis of chiral Tb³⁺ complexes using a similar binary modular strategy, the relevant literature on heteroleptic binary Tb³⁺-based systems is very scarce and mainly limited to a few tris-β-diketonate-based and coumarin-based Tb³⁺ complexes [18,19,20,21,22] with point-chiral/planar-chiral auxiliary ligands with low B_CPL values (B_CPL ≤ 11.7 M⁻¹ cm⁻¹ at ⁵D₄→⁷F₅; see Table S1).

Herein, we have combined a strong point-chiral auxiliary ligand, such as the commercially available enantiopure 2,6-bis(4-phenyl-2-oxazolin-2-yl) pyridine (R,R/S,S-Ph-PyBox), with efficient sensitizing chromophores to increase the B_CPL of organo-Tb³⁺ molecules with a heteroleptic binary molecular design. We use pyrazolone 1-phenyl-3-methyl-4-(isobutyryl)-5-pyrazolone (HPMIP) as the chromophore, since it is one of the most widely used, highly efficient anionic organic antennae for sensitizing Tb³⁺-characteristic luminescence (generally, Φ_PL ≥ 30%) with strong π→π^* transitions located in the near-UV region [23,24,25]. The CPL properties of such a chiral pyrazolate-Tb³⁺ system have not been experimentally demonstrated yet. Here, we report the synthesis, characterization, photophysical properties, and theoretical calculations of a novel pair of mononuclear chiral nine-coordinate tris-pyrazolate-Tb³⁺ enantiomers, denoted as [Tb(PMIP)₃(R,R-Ph-PyBox)] (2) and [Tb(PMIP)₃(S,S-Ph-PyBox)] (5), respectively (see Scheme 1). In addition to the intense CPL activity (|g_lum| = 0.096–0.103) associated with the excited-state chiroptical properties of the Tb³⁺ enantiomers, significantly enhanced B_CPL values (610–623 M⁻¹ cm⁻¹ at ⁵D₄→⁷F₅) of the high-purity green luminescence were also achieved. The analogous La³⁺/Gd³⁺ enantiomers were also synthesized to establish the liquid-state structure and the lowest electronic state energy levels of the chiral Ln³⁺ assemblies.

2. Results and Discussion

2.1. Synthesis and Characterization

Using the traditional self-assembly procedure in a solution, a series of precursor complexes [Ln(PMIP)₃(H₂O)₂] (Ln = La, Tb, and Gd) were successfully prepared by the reaction of Lanthanide salts (LnCl₃·6H₂O) with HPMIP ligands in a 1:3 stoichiometry in the presence of NaOH. To introduce the optical and stereochemical chirality, the tridentate enantiopure bis(oxazoline) derivative R,R-Ph-PyBox or S,S-Ph-PyBox was introduced to fill the second coordination sphere of Ln³⁺ ions. The two series of compact saturated nine-coordinate chiral organo-Ln³⁺ complexes, [Ln(PMIP)₃(R,R-Ph-PyBox)] (Ln = La, 1; Tb, 2; Gd, 3) and [Ln(PMIP)₃(S,S-Ph-PyBox)] (Ln = La, 4; Tb, 5; Gd, 6), were obtained as colorless polycrystalline particles in high chemical yields (68–76%). The synthetic procedures of the pyrazolone ligand HPMIP, [Ln(PMIP)₃(H₂O)₂] precursors, and corresponding chiral Ln³⁺ complexes 1–6 are given in Scheme 1.

The resulting HPMIP ligand, [Ln(PMIP)₃(H₂O)₂] precursors, and chiral Ln³⁺ complexes 1–6 are fairly soluble in most common organic solvents (CH₃OH, CH₃CN, and CH₂Cl₂, etc.) and have been fully structurally characterized with a combination of EA, FTIR, ¹H NMR, and MS spectroscopy techniques. The MALDI-TOF MS in positive-ion mode shows a series of parent peak signals with mass-to-charge ratios (m/z) of 1237.356, 1257.425, 1256.562, 1237.612, 1257.258, and 1256.651, which can unambiguously be assigned to single-charged cations [Ln(PMIP)₃(Chiral-Ph-PyBox)]⁺ of 1–6, respectively, indicating that the series of chiral Ln³⁺ complex molecules is structurally stable in a CH₃CN solution. The ¹H NMR spectra (400 MHz, CDCl₃, 298 K) of the diamagnetic La³⁺ enantiomers and the associated free ligands are shown in Figure 1 and Figure S1. Relative to the free HPMIP (δ = 7.82–1.25 ppm) and Chiral-Ph-PyBox (δ = 8.34–4.41 ppm) ligands, the enantiopure La³⁺ assemblies exhibit a total of 12 significantly broadened resonances with moderate high-field shifts in the chemical shift range of 8.22–0.69 ppm. Additionally, the 3:1 integration ratio between the deprotonated (PMIP)⁻ anionic ligands and the chiral auxiliary R,R-Ph-PyBox or S,S-Ph-PyBox ligand is consistent with the stoichiometry of the binary tris-pyrazolate-Tb³⁺ compound, [Ln(PMIP)₃(Chiral-Ph-PyBox)], confirming the successful synthesis of the targeted Ln³⁺ molecule. Thermal analyses indicated that the two Tb³⁺ enantiomers have high decomposition temperatures (ΔT_5% = 272–274 °C; Figure S2), showing excellent thermal stability.

2.2. Ground-State Optical Properties

The UV−vis absorption and circular dichroism (CD) spectra of the free ligands and corresponding Tb³⁺/Gd³⁺ enantiomers were recorded in a chromatographic-grade CH₃CN solution (c = 1.0 × 10⁻⁵ mol/L) at room temperature. Identical near-UV absorption behaviors (Figure 2a and Figure S3) for each pair of enantiomers (Chiral-Ph-PyBox and Tb³⁺/Gd³⁺ enantiomers) were observed, indicating that the chirality of the stereogenic centers that are localized at the bis(oxazoline) moieties has little influence on their ground-state photophysical properties [26]. Compared to the near-UV absorption bands (λ_abs = 234 and 266 nm; Figure S3) of free HPMIP, the two Tb³⁺ enantiomers also display a pair of ligand-centered absorption bands at 235 and 263 nm. The stronger lower-energy absorption band at 263 nm (ε_{263 nm} = 38,400–39,500 M⁻¹ cm⁻¹; see

Table 1. Summary of the circularly polarized green luminescence metrics for 2 and 5.

Compound	λem (nm)	ε263 nm (M−1 cm−1)	ΦPL	Transition	|glum|	βi	BCPL (M−1 cm−1) a
2	490	38,400	47%	5D4→7F6	0.013	0.15	18
	545			5D4→7F5	0.103	0.67	623
5	490	39,500	48%	5D4→7F6	0.015	0.15	21
	545			5D4→7F5	0.096	0.67	610

^a Calculated using the following formula: B_CPL = β_i × ε_λ × Φ_PL × |g_lum|/2 (details of the β_i and ε_λ metrics are given in the Supplementary Materials).

) is attributed to the singlet−singlet π-π^* enol absorption of the β-diketonate moieties in the deprotonated (PMIP)⁻ ligands [27]. The blue shift (ca. 3 nm) of this band can be attributed to the decrease in the π-conjugation in the coupled (PMIP)⁻ due to the twisted complexation of (PMIP)⁻ to the Tb³⁺ ions [28]. As shown in Figure 2b, a pair of obvious mirror-imaged Cotton-effect bands ((+)-256 and (−)-286 nm for 2; (−)-257 and (+)-285 nm for 5) from the π-π^* electronic transitions of the achiral diketonate moieties of the (PMIP)⁻ ligands were also observed, suggesting that the chirality was successfully introduced in the ground-state of the (PMIP)⁻ ligands through the coordination of Chiral-Ph-PyBox to the achiral [Tb(PMIP)₃(H₂O)₂] moiety [29].

2.3. Excited-State Optical Properties

The photoluminescence (PL) and CPL spectra of the Tb³⁺/Gd³⁺ enantiomers were measured under identical conditions as that for the ground-state absorption measurements. The excitation spectra of the two Tb³⁺ enantiomers show absorption peaks at ca. 330 nm (Figure S4), assigned to the excitation of the pyrazolone antennae moieties. The corresponding PL and CPL spectra in Figure 3 were recorded at ca. 330 nm excitation from enantiomer pairs 2 and 5. The PL spectra (Figure 3a) clearly show a set of distinct Stark splitting narrow line-like bands at 490, 545, 585, and 621 nm, ascribed to the emissions from the ⁵D₄ emissive state to the low-lying ⁷F_J multiple states of Tb³⁺ ions with the corresponding J = 6–3, respectively. The absence of any residual ligand-based fluorescence emission in the expected energy range indicates a complete transfer of the absorbed energy from the excited π-states of the ligands ((PMIP)⁻ and Chiral-Ph-PyBox) to the Tb³⁺ ions [30]. This energy transfer (ET) mechanism will be discussed later. The emission peaks associated with ⁵D₄→⁷F_4,3 transitions offer relatively low intensities, as they are partially or fully forbidden both in the MD or ED transitions [30]. In contrast, the stronger emissions based on the ⁵D₄→⁷F₆ and ⁵D₄→⁷F₅ transitions are ED- and MD-allowed, respectively. The observed hypersensitive ⁵D₄→⁷F₅ transitions (β_i = 67%; see Table 1) dominate the entire PL spectra from the two Tb³⁺ enantiomers, offering a brilliant Tb³⁺-centered high-purity green luminescence with Commission Internationale de l’Eclairage (CIE) chromaticity coordinates (Figure 3b,c) of x = 0.310–0.311 and y = 0.608. This bright PL luminous behavior is reflected by their corresponding high overall quantum yields (Figures S5 and S6) of 47% for 2 and 48% for 5, which are almost comparable to the reported achiral tris-β-diketonate [31,32] and tris-pyrazolate Tb³⁺ complexes [23,24,25,33]. Significantly, they are much higher than any reported CPL-active heteroleptic Tb³⁺ emitter, with the exception of coumarin-based Tb³⁺ complexes (Φ_PL = 55%; Table S1) [22].

The time-resolved emission profiles of the hypersensitive ⁵D₄→⁷F₅ transition were characterized for the two Tb³⁺ enantiomers in a chromatographic-grade CH₃CN solution (c = 1.0 × 10⁻⁵ mol/L) at room temperature. The decay curves were analyzed using a single exponential function, which gives the effective lifetime values of 798 and 795 μs for 2 and 5 (Figures S7 and S8). The excellent fitting with a single exponential decay function and μs lifetime indicates the involvement of one major monomeric configuration species in the solution with intrinsic long-lived phosphorescent properties [34,35]. The two Tb³⁺ enantiomers offer a pair of high-resolution quasi-mirror-imaged CPL profiles (Figure 3d) with positive–negative peaks related to the ⁵D₄→⁷F_J (J = 6–3) transitions, agreeing with the corresponding PL spectra. Both the electronic structure of the Ln³⁺ ion and the crystal field affect the CPL activity of the chiral Ln³⁺ compounds. The high g_lum values can usually be achieved for MD-allowed and ED-forbidden transitions [36]. The ⁵D₄→⁷F_6,4,3 transitions are expected to be less CPL-active, whereas the MD ⁵D₄→⁷F₅ transitions offer the most intense CPL bands, as confirmed from the CPL spectra in Figure 3d. This is also confirmed by the bisignate pattern of the g_lum values (Figure S9) of +0.103 and −0.096 for 2 and 5, respectively. Such high g_lum values are comparable to the chiral PyBox-based Ln³⁺ complexes [14,17,19,37], representing one of the best chiroptical performance metrics from the organo-Tb³⁺ complexes using chiral–auxiliary ligands [18,19,20,21,38,39,40]. The relatively high g_lum, combined with three other excellent optical metrics of β_i, ε_λ, and Φ_PL, yield strong B_CPL values (Table 1) for the ⁵D₄→⁷F₅ transitions, reaching 623 and 610 M⁻¹ cm⁻¹ for 2 and 5. To our knowledge, these B_CPL values represent the best performance for heteroleptic chiroptical Tb³⁺ emitters [13], as shown in Table S1.

It is well established that the energy match within the organo-Tb³⁺ complexes is the key factor affecting luminescence behaviors. To elucidate the ET mechanism of the effective sensitization in our Tb³⁺ complexes, the energy levels of the relevant lowest excited states should be evaluated. Since the emission level of Gd³⁺ ion is very high (32,000 cm⁻¹), the sensitization of the Gd³⁺ ion by an organic ligand is not possible. Therefore, the energy levels of the lowest triplet-excited state (³π-π^*) of the luminescent Ln³⁺ complexes can be determined from the shorter-wavelength emission peaks (λ_em = 429 and 431 nm, respectively; Figure S10) from the corresponding isostructural Gd³⁺ complexes recorded at 77 K [41]. The ³π-π^* energy levels of complexes 3 and 6 are determined to be 23,310 and 23,201 cm⁻¹, respectively, which are consistent with the theoretical calculation results (vide infra). The lowest singlet-excited state (¹π-π^*) energy levels of 28,818 cm⁻¹ for 2 and 5 were estimated from their UV−vis absorbance edges (λ_edge = 347 nm) [42]. The relevant ¹π-π^*/³π-π^* energy levels, along with a possible intramolecular Dexter ET mechanism, are presented in Figure 4. In light of Reinhoudt’ and Latva’s empirical rules [43,44], an effective singlet–triplet intersystem crossing (ISC) process can be achieved due to the energy gaps between the ¹π-π^* and ³π-π^*, ΔE¹ = E(¹π-π^*) − E(³π-π^*) = 5508 and 5617 cm⁻¹, for complexes 2 and 5, which are slightly greater than 5000 cm⁻¹. The energy differences between ³π-π^* and the first Tb³⁺ excited ⁵D₄-emitting state at 20,500 cm⁻¹, calculated from ΔE² = E(³π-π^*) − E(⁵D₄), are 2701 and 2810 cm⁻¹ for complexes 5 and 2, indicating that the ET process from ligand to Tb³⁺ (LMET; ³π-π^*→⁵D₄) is possible, while there is no reverse energy transfer (EBT; ⁵D₄→³π-π^*) from the ⁵D₄-emitting level to the ³π-π^*.

2.4. Theoretical Calculations of Electronic Structure

To establish the photophysical properties of the two chiral Tb³⁺ enantiomers, density functional theory (DFT) calculations of the diamagnetic La³⁺ enantiomers were carried out based on the Becke–Lee–Yang–Parr (B3LYP) hybrid function because of the presence of uncoupled f electrons for Tb³⁺ ions [45,46]. The resultant minimum-energy structures, along with their respective frontier molecular orbitals HOMOs and LUMOs’ energy levels and electron density distributions, are shown in Figure 5 and Table S2. Moreover, time-dependent DFT (TD-DFT) calculations of the DFT-optimized structures were also performed to simulate the UV-vis absorption behavior of the Ln³⁺ enantiomers. The calculated absorption wavelengths (λ/nm), oscillator strengths (f), electronic vertical excitation energies (E/eV), transition types, and property details were established by interfragment charge transfer (IFCT) analysis and are summarized in Table S3.

It can be clearly seen that the orbital density distributions of the HOMOs and LUMOs in two chiral La³⁺ enantiomers are not affected by the participation of enantiopure R,R-Ph-PyBox, or S,S-Ph-PyBox ligands with nearly identical distribution patterns (see Figure 5 and Table S2). The LUMO distributions for 1 (98.09%) and 4 (98.05%) are almost exclusively localized on the Chiral-Ph-PyBox ligands. The corresponding HOMO distributions of complexes 1 and 4 are localized at the (PMIP)⁻-1 ligand with ca. 44.03 and 45.02%, respectively. Meanwhile, the (PMIP)⁻-2 constitutes 53.41 and 53.23% of complexes 1 and 4, respectively. The theoretical HOMO and LUMO energy levels are in good agreement with the experimentally determined energy levels (E_HOMO = −5.44/−5.43 eV; E_LUMO = −1.87/−1.86 eV) that were estimated from the optical HOMO-LUMO gap values (E_g^opt = 3.57 eV) and the oxidation potentials (E_ox^onset = 1.15–1.16 V) from the cyclic voltammogram (versus an Fc/Fc⁺ couple; Figure S11 and Table S4). According to the TD-DFT calculations of the S₀→S₁ excitation (Table S3), the lowest-energy absorption bands in the UV-vis spectra of complexes 1–6 can be attributed to the singlet ligand-to-ligand charge transfer (¹LLCT) with a dominant HOMO→LUMO (97.47% for 1 and 96.38% for 4), mainly involving (PMIP)⁻-1→Chiral-Ph-PyBox and (PMIP)⁻-2→Chiral-Ph-PyBox mixed-transition contributions. In the calculated lowest-energy vertical S₀→T₁ transitions, two theoretical lowest triplet-excited state energy levels of 22,779 cm⁻¹ for 1 and 22,831 cm⁻¹ for 4 were calculated, which are close to the experimental values (23,201 and 23,310 cm⁻¹) that were estimated from corresponding phosphorescence spectra of Gd³⁺ enantiomers, measured at 77 K.

3. Materials and Methods

3.1. General Information and Synthesis of Intermediates

Analytically pure and chromatographic-grade solvents were used for synthesis and spectral measurements, respectively. All solvents were purchased from Tianjin Fuyu Fine Chemical Co. (Tianjin, China). 1-phenyl-3-methyl-5-pyrazolone (PMP), isobutyryl chloride, R,R-Ph-PyBox, S,S-Ph-PyBox, and trivalent Lanthanide chloride hexahydrate salts (99.99% for LaCl₃·6H₂O, TbCl₃·6H₂O, and GdCl₃·6H₂O) were purchased from Aladdin (Shanghai, China). NaOH, Ca(OH)₂, and concentrated hydrochloric acid (HCl, 37%) were supplied by Tianjin Damao Chemical Reagent Factory (Tianjin, China). The pyrazolone HPMIP ligand was synthesized by nucleophilic substitution of PMP with isobutyryl chloride in excess Ca(OH)₂, according to our previous report [47,48]. The Ln³⁺ dihydrate complex precursors [Ln(PMIP)₃(H₂O)₂] (Ln = La, Tb, and Gd) were synthesized using a traditional solution-phase self-assembly procedure [49,50]. Additional details about the synthetic procedures and the characterization of the intermediates (HPMIP and Ln³⁺ precursors) and spectroscopic measurement details are provided in the Supplementary Materials.

3.2. Synthetic Procedures and Characterizations of the Chiral Organo-Ln³⁺ Complexes 1–6

The equimolar amounts of the precursors [Ln(PMIP)₃(H₂O)₂] (0.3 mmol; Ln = La, 0.271 g; Tb, 0.277 g; Gd, 0.277 g) and enantiopure tridentate N^N^N-donor R,R-Ph-PyBox (0.111 g, 0.3 mmol) or S,S-Ph-PyBox (0.111 g, 0.3 mmol) ligand were dissolved in CH₃OH (30 mL) in a reaction flask. Each reaction mixture was stirred at 95 °C for 12 h. The resulting solution was left at an ambient temperature for crystallization, and the colorless polycrystalline products of 1–6 were obtained after the solution had evaporated for 3–4 days.

The analysis data for 1 are as follows: Yield = 0.260 g, 70%. Anal. Calcd. for C₆₅H₆₄N₉O₈La: C, 63.05; H, 5.21; N, 10.18%. Found: C, 63.11; H, 5.17; N, 10.26%. FTIR (KBr, cm⁻¹): 3439 (w), 2961 (w), 2920 (w), 2859 (w), 1619 (vs), 1587 (m), 1533 (w), 1493 (s), 1443 (m), 1365 (m), 1317 (w), 1267 (w), 1236 (w), 1183 (w), 1138 (w), 1089 (w), 1064 (w), 1024 (w), 980 (m), 920 (m), 830 (w), 755 (m), 695 (w), 650 (m), 614 (w), 545 (w), 507 (w), 429 (w). ¹H NMR (CDCl₃, 400 MHz, 298 K): δ (ppm) 8.22 (m, 2H, -Py), 8.21 (t, 1H, -Py), 7.80 (s, 6H, -Ph), 7.09 (s, 7H, -Ph), 6.96 (t, 5H, -Ph), 6.82 (d, 7H, -Ph), 5.32 (d, 2H, -H^j), 4.72 (t, 2H, -CH₂ of -H^k), 4.21 (s, 2H, -CH₂ of -H^k), 2.80 (s, 3H, -H^d), 2.27 (s, 9H, -H^e), 0.69 (s, 18H, -H^f). MALDI-TOF MS: m/z 1237.356 (100%), [M-H]⁺.

The analysis data for 2 are as follows: Yield = 0.276 g, 73%. Anal. Calcd. for C₆₅H₆₄N₉O₈Tb: C, 62.05; H, 5.13; N, 10.02%. Found: C, 62.12; H, 5.17; N, 9.97%. FTIR (KBr, cm⁻¹): 3446 (w), 2964 (w), 2921 (w), 2860 (w), 1619 (vs), 1586 (m), 1532 (w), 1491 (s), 1444 (m), 1364 (m), 1318 (w), 1267 (w), 1237 (w), 1183 (w), 1138 (w), 1089 (w), 1064 (w), 1022 (w), 979 (m), 919 (m), 830 (w), 754 (m), 695 (w), 651 (m), 614 (w), 546 (w), 506 (w), 428 (w). MALDI-TOF MS: m/z 1257.425 (100%), [M-H]⁺.

The analysis data for 3 are as follows: Yield = 0.278 g, 74%. Anal. Calcd. for C₆₅H₆₄N₉O₈Gd: C, 62.13; H, 5.13; N, 10.03%. Found: C, 62.18; H, 5.01; N, 10.08%. FTIR (KBr, cm⁻¹): 3441 (w), 2960 (w), 2921 (w), 2858 (w), 1619 (vs), 1588 (m), 1534 (w), 1492 (s), 1443 (m), 1365 (m), 1318 (w), 1268 (w), 1235 (w), 1182 (w), 1139 (w), 1090 (w), 1063 (w), 1025 (w), 980 (m), 919 (m), 828 (w), 755 (m), 696 (w), 649 (m), 614 (w), 546 (w), 507 (w), 427 (w). MALDI-TOF MS: m/z 1256.562 (100%), [M-H]⁺.

The analysis data for 4 are as follows: Yield = 0.252 g, 68%. Anal. Calcd. for C₆₅H₆₄N₉O₈La: C, 63.05; H, 5.21; N, 10.18%. Found: C, 63.13; H, 5.27; N, 10.12%. FTIR (KBr, cm⁻¹): 3442 (w), 2959 (w), 2920 (w), 2859 (w), 1618 (vs), 1586 (m), 1532 (w), 1494 (s), 1444 (m), 1367 (m), 1317 (w), 1267 (w), 1236 (w), 1182 (w), 1138 (w), 1089 (w), 1064 (w), 1023 (w), 979 (m), 918 (m), 830 (w), 755 (m), 695 (w), 649 (m), 615 (w), 546 (w), 506 (w), 428 (w). ¹H NMR (CDCl₃, 400 MHz, 298 K): δ (ppm) 8.22 (m, 2H, -Py), 8.20 (t, 1H, -Py), 7.80 (s, 6H, -Ph), 7.10 (s, 7H, -Ph), 6.96 (t, 5H, -Ph), 6.82 (d, 7H, -Ph), 5.32 (d, 2H, -H^j), 4.72 (t, 2H, -CH₂ of -H^k), 4.21 (s, 2H, -CH₂ of -H^k), 2.80 (s, 3H, -H^d), 2.28 (s, 9H, -H^e), 0.69 (s, 18H, -H^f). MALDI-TOF MS: m/z 1237.612 (100%), [M-H]⁺.

The analysis data for 5 are as follows: Yield = 0.286 g, 76%. Anal. Calcd. for C₆₅H₆₄N₉O₈Tb: C, 62.05; H, 5.13; N, 10.02%. Found: C, 62.14; H, 5.15; N, 9.95%. FTIR (KBr, cm⁻¹): 3445 (w), 2963 (w), 2919 (w), 2860 (w), 1618 (vs), 1587 (m), 1533 (w), 1494 (s), 1443 (m), 1364 (m), 1317 (w), 1267 (w), 1237 (w), 1183 (w), 1138 (w), 1089 (w), 1064 (w), 1025 (w), 981 (m), 919 (m), 829 (w), 754 (m), 695 (w), 650 (m), 614 (w), 546 (w), 508 (w), 427 (w). MALDI-TOF MS: m/z 1257.258 (100%), [M-H]⁺.

The analysis data for 6 are as follows: Yield = 0.271 g, 72%. Anal. Calcd. for C₆₅H₆₄N₉O₈Gd: C, 62.13; H, 5.13; N, 10.03%. Found: C, 62.16; H, 5.02; N, 10.11%. FTIR (KBr, cm⁻¹): 3440 (w), 2960 (w), 2919 (w), 2859 (w), 1620 (vs), 1586 (m), 1533 (w), 1492 (s), 1444 (m), 1364 (m), 1316 (w), 1267 (w), 1236 (w), 1183 (w), 1139 (w), 1089 (w), 1064 (w), 1024 (w), 981 (m), 920 (m), 831 (w), 756 (m), 694 (w), 649 (m), 614 (w), 544 (w), 507 (w), 429 (w). MALDI-TOF MS: m/z 1256.651 (100%), [M-H]⁺.

4. Conclusions

In conclusion, the coupling of an enantiopure bis(oxazoline) derivative (R,R-Ph-PyBox or S,S-Ph-PyBox) successfully induced CD and CPL properties in well-developed chromophoric [Tb(PMIP)₃(H₂O)₂] systems. This led to the design and synthesis of the first example of CPL-active pyrazolonate-Tb³⁺ molecules with bright Tb³⁺-centered high-purity green emission (Φ_PL = 47–48%) and intense excited-state chiroptical activity (|g_lum| = 0.096–0.103). The diastereopurity of the complexes (2 or 5) in a solution was confirmed through various techniques, including the chiroptical spectra, single exponential decay responses, and hydrogen proton resonance distribution. Optical characterizations and theoretical calculations highlighted that coordinating two types of ligands with distinct functions to the Tb³⁺ ions enhances the antenna-centered light absorption in the π-π^* electronic transition range and conveys a one-way complete energy to the central Tb³⁺ ions. By balancing key metrics (β_i, ε_λ, Φ_PL and g_lum), the highest B_CPL (up to 623 M⁻¹ cm⁻¹ for 2) was achieved for the CPL-active heteroleptic Tb³⁺ emitters. This promising outcome suggests that further structural optimization of heteroleptic binary Ln³⁺ molecules could further enhance their CPL properties, delivering a higher B_CPL value for circularly polarized monochromatic green luminescence.