•PLY and its isomer 1 radicals can form stable hetero-dimers.•The effect of boron and nitrogen substitution induces intermolecular charge-transfer.•Larger intermolecular charge-transfer significantly enhance second-order NLO properties.•The first hyperpolarizability density study clearly substantiates the difference in their βzzz values.Recently, the structure-property relationships of an attractive isomeric radical 1 (Phys. Chem. Chem. Phys., 2016, 18, 29041–29044) with famous phenalenyl (PLY) was investigated. Can PLY and 1 form stable π-dimers? The single point energy scan result shows that the staggered π-dimer (2) has the lowest energy. In order to explore intermolecular charge-transfer and nonlinear optical property, two π-dimers (2a and 2b by boron and nitrogen atoms substituting the central carbon atoms of 2) are designed. 2 has smaller intermolecular charge-transfer (0.020) and the first hyperpolarizability (βtot, 3.18 × 102 au). However, boron and nitrogen substitution effect can greatly enhance intermolecular charge-transfer (0.215 for 2a and 0.181 for 2b) and the βtot values (6.32 × 103 for 2a and 6.80 × 103 for 2b). Interestingly, the βtot values of 2a and 2b are close to each other, but their βz components and the NBO charge analysis show that 2a and 2b have opposite direction of charge transfer, which can be well explained by the difference of the dipole moment component (Δμz) between the ground and the excited states. Further, the first hyperpolarizability density study clearly substantiates the difference in their βzzz values: negative contribution for 2a is much larger than positive contribution, while the first hyperpolarizability density for 2b shows much larger positive contribution. Thus, the primary component of βzzz is negative value for 2a and βzzz is positive value for 2b. Combining with the frontier molecular orbital (FMO) and the electron density difference map (EDDM), intermolecular charge-transfer transition from B substituted fragment to N substituted fragment for 2a and 2b is concluded. The significant structure-property relationships in present π-dimers are beneficial for further theoretical and experimental investigations of high-performance nonlinear optical materials.The effect of boron and nitrogen substitution induces intermolecular charge-transfer, which significantly enhance second-order NLO properties of hetero-dimers with the aid of the DFT calculations.Download high-res image (266KB)Download full-size image

Very recently, the investigation of an Li atom doped effect on the “through-space” electronic interaction (S) of a donor–S–acceptor (D–S–A, 1) shows that the Li-doping effect can modulate the first hyperpolarizability of 1 ( Dyes Pigm. 2014, 106, 7−13). Can we further enhance the first hyperpolarizability (βtot) of 1 by modulating the charge transfer of D–S–A molecules? The present work indicates that the βtot value can be successfully modulated by replacing the sp2-hybridized CH═CH moiety connected with substituted para-cyclophane (PCP). On the other hand, the NO2 contributes more than NH2 to the βtot value. The results of time-dependent density functional theory (TD-DFT) provide a good explanation for the variation in the βtot value. Interestingly, the βtot value of 3 (4.09 × 103 au) is larger than 1.52 × 103 au of 4, while the difference between the dipole moments (Δμ) of the ground state and the crucial excited state of 3 (2.93 D) is smaller than that of 4 (7.79 D). Further, the charge-transfer excitation length (DCT) of 3 (1.41 Å) is smaller than that of 4 (2.89 Å). Therefore, DCT is the major factor in determining the Δμ value.

Due to unpaired electrons, both radicals and superalkali are investigated widely. In this work, two interesting complexes (Li3O-PLY and Li3-PLY) were constructed by phenalenyl radical and superalkali atoms. Why are they interesting? Firstly, for Li3O-PLY and Li3-PLY, although the charge transfer between superalkali atoms and PLY is similar, the sandwich-like charge distribution for Li3O-PLY causes a smaller dipole moment than that of Li3-PLY. Secondly, their UV–vis absorption show that the maximum wavelengths for Li3O-PLY and Li3-PLY display a bathochromic shift compared to PLY. Moreover, Li3-PLY has two new peaks at 482 and 633 nm. Significantly, the β0 values of Li3-PLY (4943–5691 a.u.) are much larger than that of Li3O-PLY (225–347 a.u.). Further, the βHRS values of Li3O-PLY decrease slightly while βHRS of Li3-PLY increase dramatically with increasing frequency. It is our expectation that these results might provide beneficial information for theoretical and experimental studies on complexes with superalkali and PLY radicals.

Recently, the crystal structures and electrochemical properties of the isomers (Sc2S “trapped” in C82) have been reported, in which the Sc2S is located inside the different positions of the C82 cage. In the present work, three isomers of endohedral metallofullerenes Sc2S@C3v(8)-C82 (A, B, and C) have been designed to explore the effect of the position of Sc2S on their interaction energies and nonlinear optical properties. Among three isomers, the Sc2S is located in different positions of the C82 cage: the angles of Sc–S–Sc in A, B, and C are 104.9, 114.8, and 115.7°, respectively. Furthermore, the analysis of natural bond orbital (NBO) charge indicates that the electron-transfer is from the Sc2S to the adjacent carbon atoms of the C82 cage. The interaction energy of B is the smallest among three isomers which is −226.2 kcal mol-1. It was worth mentioning that their first hyperpolarizabilities (βtot) were studied, we found that their βtot values were related to the positions of Sc2S: C (2100) > B (1191) > A (947 au). We hope that the present work can provide a new strategy to promote the nonlinear optical properties of endohedral metallofullerenes by changing the positions of the encapsulated molecular.

Recently, two isomeric thiophene-fused benzocarborane derivatives Tb1 and Tb2 with different locations of sulfur atoms, labeled as 1, 4 and 6, 9 of the thiophene were synthesized by Morisaki (Chem.–Eur. J., 2012, 18, 11251–11257) and Barrere (Macromolecules, 2009, 42, 2981–2987), respectively. In the present work, natural bond orbital (NBO) analysis shows that after doping one lithium atom into the isomeric structures Tb1 and Tb2, the electrons transfer to different regions in Tb1 and Tb2. For Tb1-Li, the transferred electrons mainly locate at S1, C2, C3, and S4, but for Tb2-Li, the transferred electrons mainly locate at C2, C3, C7, and C8. Significantly, the charge distribution is a crucial factor influencing the static first hyperpolarizabilities for Tb1-Li and Tb2-Li. Furthermore, the βtot value of Tb1-Li is 6222 au, which is about 160 times larger than that of Tb1 (39 au). However, the βtot value of Tb2-Li (498 au) is only about 5 times larger than that of the corresponding Tb2 (91 au). It is our expectation that this work could provide useful information for the development of nonlinear optical materials based on carboranes.

•Three complexes were designed by doping Li atom into D-S-A(1) for the first time.•In 1-Li-Mid, intermediate cavity hinders the polarization of Li atom.•The most negative NICS value of 1-Li-Mid is −52.0 ppm.•The direction of crucial transition is the important factor for βtot value.•Resonances in Li-doped D-S-A molecules resulting in huge βHRS(−2ω;ω,ω) value.In the present work, three complexes(1-Li–NO2, 1-Li-Mid and 1-Li–NH2) were designed by doping Li atom into the different location(above, middle and below) of the novel noncovalent “through-space” electronic interaction (S) of Donor-S-Acceptor (1) to explore their structure-property relationships. The results show that doping Li atom can obviously enhance the first hyperpolarizability (βtot) of 1. Interestingly, the crucial transition direction of 1-Li–NH2 is from donor group to acceptor group, which is opposite to those of 1-Li–NO2 and 1-Li-Mid. The highest occupied molecular orbital (HOMO) of 1-Li–NH2 shows that doping one Li atom enhances the π–π interaction resulting in the largest βtot value (1.50 × 105) which is about 16 times larger than that of 1(9.13 × 103) and is also obviously larger than those of 1-Li-Mid(5.81 × 104) and 1-Li–NO2(6.45 × 104 au). The results indicate that 1-Li–NH2 can be considered as a novel high-performance NLO material and the location of Li atom can modulate NLO response.In the present work, three complexes (1-Li–NO2, 1-Li-Mid and 1-Li–NH2) were designed by doping Li atom into the location (above, middle and below) of the S of 1 to explore their structures, aromaticities and nonlinear optical properties.

Assembly with large nonlinear optical response of the novel sandwich-like supermolecules CpLi-C60 (Cp = cyclopentadienide) has been investigated for two pathways. First, the half-sandwich Li salt CpLi is formed, and then the sandwich-like supermolecules CpLi-C60(trans) and CpLi-C60(cis) are obtained by affixing the C60 to CpLi. The results indicate that the βtot values of CpLi-C60(trans) (14 093 au) and CpLi-C60(cis) (15 560 au) increase sharply to about 22 times and 25 times greater than that of CpLi (624 au), respectively. This shows that the whole supermolecule is lighted by C60. Second, a Li atom is added to C60 to form the half-sandwich-like Li-C60, and then we attach the Cp to Li-C60 to form CpLi-C60(trans) and CpLi-C60(cis). The results indicate that the βtot values of CpLi-C60(trans) and CpLi-C60(cis) increase sharply to about 10 times and 11 times greater than that of Li-C60 (1387 au), respectively. Then, the two supermolecule Li salts are expected to be molecular switches by rotation of Cp. Notably, the interaction energies (Eint) of CpLi-C60(trans) and CpLi-C60(cis) are about −101 and −100 kcal/mol, which implies that they are more stable than Li-C60 (−38 kcal/mol). The present work proposes a new strategy for designing high-performance nonlinear optical materials and provides a new way to assemble sandwich supermolecule salts.

Density functional theory (DFT) B3LYP method was employed to calculate electron properties and the second-order nonlinear optical (NLO) responses of the derivatives which were formed by (C5H5)Co(C2B4H6) and CHCHC6H4NO2, CHCHC6H4NH2. The results show: when H atom of (C5H5)Co(C2B4H6) is substituted by CHCHC6H4NO2, the βtot values of isomers are all slightly smaller than that of ferrocene (Fc) derivative (FcCHCHC6H4NO2). However, when H atom of (C5H5)Co(C2B4H6) is substituted by CHCHC6H4NH2, the βtot values of isomers are close to that of ferrocene (Fc) derivative (FcCHCHC6H4NH2). It indicates that (C5H5)Co(C2B4H6) can be either a donator or an acceptor.

Recently, two isomeric thiophene-fused benzocarborane derivatives Tb1 and Tb2 with different locations of sulfur atoms, labeled as 1, 4 and 6, 9 of the thiophene were synthesized by Morisaki (Chem.–Eur. J., 2012, 18, 11251–11257) and Barrere (Macromolecules, 2009, 42, 2981–2987), respectively. In the present work, natural bond orbital (NBO) analysis shows that after doping one lithium atom into the isomeric structures Tb1 and Tb2, the electrons transfer to different regions in Tb1 and Tb2. For Tb1-Li, the transferred electrons mainly locate at S1, C2, C3, and S4, but for Tb2-Li, the transferred electrons mainly locate at C2, C3, C7, and C8. Significantly, the charge distribution is a crucial factor influencing the static first hyperpolarizabilities for Tb1-Li and Tb2-Li. Furthermore, the βtot value of Tb1-Li is 6222 au, which is about 160 times larger than that of Tb1 (39 au). However, the βtot value of Tb2-Li (498 au) is only about 5 times larger than that of the corresponding Tb2 (91 au). It is our expectation that this work could provide useful information for the development of nonlinear optical materials based on carboranes.