Chiral transition metal complexes not only have large nonlinear optical (NLO) response but also meet the non-centrosymmetric requirement of second-order NLO materials. Therefore, chiral transition metal complexes become very active in the NLO area. Recently, the second-order NLO response of chiral dinuclear Re(I) complex 2 has been found to be 1.5 times larger than that of KH2PO4 (KDP) based on experimental measurement. However, its NLO origin has not been determined and a structure–property relationship has not been established at the microscopic level, which are very important to further improve the performance. It is found that charge transfer from metal to ligand is mainly responsible for its NLO origin. Based on complex 2, the designed complexes have remarkably large second-order NLO activity. For instance, the designed complex 9 has a very large second-order NLO response value (115.81 × 10−30 esu), which is about 668 times larger than the organic molecule urea. Moreover, time-dependent density functional theory (TDDFT) calculations have been used to investigate their UV-Vis/CD spectra. The simulated circular dichroism (CD) spectra of the complex 2 are in good agreement with the experimental ones, which can be used to assign the absolute configurations (ACs) of chiral dinuclear Re(I) complexes with high confidence. The electronic absorption wavelengths, electron transition properties, and the second-order NLO responses strongly depend on the nature of substituent, different ligands (pyridine and isoquinoline) and their combinations. Based on NBO analysis, the interactions between [Re(CO)3Cl] fragments and ligands are of n → σ* character.

Chiral transition metal complexes not only have large nonlinear optical (NLO) response but also meet the non-centrosymmetric requirement of second-order NLO materials. Therefore, chiral transition metal complexes become very active in the NLO area. Recently, the second-order NLO response of chiral dinuclear Re(I) complex 2 has been found to be 1.5 times larger than that of KH2PO4 (KDP) based on experimental measurement. However, its NLO origin has not been determined and a structure–property relationship has not been established at the microscopic level, which are very important to further improve the performance. It is found that charge transfer from metal to ligand is mainly responsible for its NLO origin. Based on complex 2, the designed complexes have remarkably large second-order NLO activity. For instance, the designed complex 9 has a very large second-order NLO response value (115.81 × 10−30 esu), which is about 668 times larger than the organic molecule urea. Moreover, time-dependent density functional theory (TDDFT) calculations have been used to investigate their UV-Vis/CD spectra. The simulated circular dichroism (CD) spectra of the complex 2 are in good agreement with the experimental ones, which can be used to assign the absolute configurations (ACs) of chiral dinuclear Re(I) complexes with high confidence. The electronic absorption wavelengths, electron transition properties, and the second-order NLO responses strongly depend on the nature of substituent, different ligands (pyridine and isoquinoline) and their combinations. Based on NBO analysis, the interactions between [Re(CO)3Cl] fragments and ligands are of n → σ* character.

Chiral transition metal complexes not only have large nonlinear optical (NLO) response but also meet the non-centrosymmetric requirement of second-order NLO materials. Therefore, chiral transition metal complexes become very active in the NLO area. Recently, the second-order NLO response of chiral dinuclear Re(I) complex 2 has been found to be 1.5 times larger than that of KH2PO4 (KDP) based on experimental measurement. However, its NLO origin has not been determined and a structure–property relationship has not been established at the microscopic level, which are very important to further improve the performance. It is found that charge transfer from metal to ligand is mainly responsible for its NLO origin. Based on complex 2, the designed complexes have remarkably large second-order NLO activity. For instance, the designed complex 9 has a very large second-order NLO response value (115.81 × 10−30 esu), which is about 668 times larger than the organic molecule urea. Moreover, time-dependent density functional theory (TDDFT) calculations have been used to investigate their UV-Vis/CD spectra. The simulated circular dichroism (CD) spectra of the complex 2 are in good agreement with the experimental ones, which can be used to assign the absolute configurations (ACs) of chiral dinuclear Re(I) complexes with high confidence. The electronic absorption wavelengths, electron transition properties, and the second-order NLO responses strongly depend on the nature of substituent, different ligands (pyridine and isoquinoline) and their combinations. Based on NBO analysis, the interactions between [Re(CO)3Cl] fragments and ligands are of n → σ* character.

Chiral transition metal complexes not only have large nonlinear optical (NLO) response but also meet the non-centrosymmetric requirement of second-order NLO materials. Therefore, chiral transition metal complexes become very active in the NLO area. Recently, the second-order NLO response of chiral dinuclear Re(I) complex 2 has been found to be 1.5 times larger than that of KH2PO4 (KDP) based on experimental measurement. However, its NLO origin has not been determined and a structure–property relationship has not been established at the microscopic level, which are very important to further improve the performance. It is found that charge transfer from metal to ligand is mainly responsible for its NLO origin. Based on complex 2, the designed complexes have remarkably large second-order NLO activity. For instance, the designed complex 9 has a very large second-order NLO response value (115.81 × 10−30 esu), which is about 668 times larger than the organic molecule urea. Moreover, time-dependent density functional theory (TDDFT) calculations have been used to investigate their UV-Vis/CD spectra. The simulated circular dichroism (CD) spectra of the complex 2 are in good agreement with the experimental ones, which can be used to assign the absolute configurations (ACs) of chiral dinuclear Re(I) complexes with high confidence. The electronic absorption wavelengths, electron transition properties, and the second-order NLO responses strongly depend on the nature of substituent, different ligands (pyridine and isoquinoline) and their combinations. Based on NBO analysis, the interactions between [Re(CO)3Cl] fragments and ligands are of n → σ* character.

Using the enantiomeric bis-bidentate bridging ligands (+)/(−)-2,5-bis(4,5-pinene-2-pyridyl)pyrazine (LS/LR) and depending on the ratio control of reactants, two mono- and dinuclear Eu(III)-based enantiomeric pairs with the formulae Eu(dbm)3LR/S·2H2O (LR in R-1, LS in S-1 and dbm = dibenzoylmethanato) and Eu2(dbm)6LR/S·H2O (LR in R-2 and LS in S-2) have been stereoselectively synthesized and structurally characterized. The circular dichroic (CD) spectra confirmed their chiroptical activities and enantiomeric natures. The homochiral dinuclear species represents the first example of a polynuclear lanthanide β-diketonate complexes with circular dichroic and crystallographic evidences. The photoluminescent properties studies revealed that both mono- and dinuclear Eu(III) complexes exhibited the characteristic red emissions of Eu(III) ions in the solid state (at 77 K and 300 K) and CH2Cl2 solution. Notably, the photophysical properties of the mononuclear enantiomers were superior to the dinuclear species. Interestingly, R-2 displayed a ferroelectric property at room temperature, which was not observed for R-1 due to the lack of crystalline polarity. R/S-2 are the first examples of homochiral polynuclear lanthanide complexes with luminescence and ferroelectric properties, being potential multifunctional materials.

Using the enantiomeric bis-bidentate bridging ligands (+)/(−)-2,5-bis(4,5-pinene-2-pyridyl)pyrazine (LS/LR) and depending on the ratio control of reactants, two mono- and dinuclear Eu(III)-based enantiomeric pairs with the formulae Eu(dbm)3LR/S·2H2O (LR in R-1, LS in S-1 and dbm = dibenzoylmethanato) and Eu2(dbm)6LR/S·H2O (LR in R-2 and LS in S-2) have been stereoselectively synthesized and structurally characterized. The circular dichroic (CD) spectra confirmed their chiroptical activities and enantiomeric natures. The homochiral dinuclear species represents the first example of a polynuclear lanthanide β-diketonate complexes with circular dichroic and crystallographic evidences. The photoluminescent properties studies revealed that both mono- and dinuclear Eu(III) complexes exhibited the characteristic red emissions of Eu(III) ions in the solid state (at 77 K and 300 K) and CH2Cl2 solution. Notably, the photophysical properties of the mononuclear enantiomers were superior to the dinuclear species. Interestingly, R-2 displayed a ferroelectric property at room temperature, which was not observed for R-1 due to the lack of crystalline polarity. R/S-2 are the first examples of homochiral polynuclear lanthanide complexes with luminescence and ferroelectric properties, being potential multifunctional materials.

The reaction of enantiomeric bis-bidentate bridging ligands (+)/(−)-2,5-bis(4,5-pinene-2-pyridyl)pyrazine (LS/LR) with [Re(CO)5Cl] yielded a pair of dinuclear Re(I) enantiomers formulated as [Re2(LS/LR)(CO)6Cl2]·4CH2Cl2 (R-1 and S-1, the isomers containing the respective LR and LS ligands). They were characterized by elemental analyses, IR spectra and X-ray crystallography. Circular dichroism spectra verified their chiroptical activities and enantiomeric nature. The measurements of second harmonic generation (SHG) and ferroelectric properties showed that R-1 displays a nonlinear optical (NLO) activity and ferroelectricity with a remnant polarization (Pr) of 1.6 μC cm−2 under an applied field of 7.3 kV cm−1 at room temperature. R-1 and S-1 represent the first example of polynuclear Re(I) complexes with ferroelectric properties. Notably, the Pr value is much larger than that of the reported mononuclear chiral Re(I) analogue. In particular, unlike mononuclear Re(I) complexes of the type [Re(CO)3(N^N)(X)] (N^N = diimine and X = halide), which usually exhibit an intense emission in the visible range, R-1 and S-1 do not show any detectable emission at any temperature range and the reason for the nonluminescence of R-1 and S-1 was further elucidated in this work. Moreover, our research results also elucidated that Re nuclearity has a great influence on not only the emitting properties but also on ferroelectric behavior.

The reaction of enantiomeric bis-bidentate bridging ligands (+)/(−)-2,5-bis(4,5-pinene-2-pyridyl)pyrazine (LS/LR) with [Re(CO)5Cl] yielded a pair of dinuclear Re(I) enantiomers formulated as [Re2(LS/LR)(CO)6Cl2]·4CH2Cl2 (R-1 and S-1, the isomers containing the respective LR and LS ligands). They were characterized by elemental analyses, IR spectra and X-ray crystallography. Circular dichroism spectra verified their chiroptical activities and enantiomeric nature. The measurements of second harmonic generation (SHG) and ferroelectric properties showed that R-1 displays a nonlinear optical (NLO) activity and ferroelectricity with a remnant polarization (Pr) of 1.6 μC cm−2 under an applied field of 7.3 kV cm−1 at room temperature. R-1 and S-1 represent the first example of polynuclear Re(I) complexes with ferroelectric properties. Notably, the Pr value is much larger than that of the reported mononuclear chiral Re(I) analogue. In particular, unlike mononuclear Re(I) complexes of the type [Re(CO)3(N^N)(X)] (N^N = diimine and X = halide), which usually exhibit an intense emission in the visible range, R-1 and S-1 do not show any detectable emission at any temperature range and the reason for the nonluminescence of R-1 and S-1 was further elucidated in this work. Moreover, our research results also elucidated that Re nuclearity has a great influence on not only the emitting properties but also on ferroelectric behavior.