Probing the REDOX effect of helical tetraspirobenzene on nonlinear optical properties

The helical structure is a classical framework to design high-performance organic electro-optical materials. In this work, the structure-property’s relationships of helical tetraspirobenzene (1) and its oxidation (12+) and reduction (12–) products are explored. The results show that the redox brings some distinctive changes in their geometric structure and electronic property, which regulate the first hyperpolarisability (βtot). Among these structures, the 12– has the largest βtot value of 4.2 × 104, which is greatly larger than 2.0 × 102 a.u. of. 12+. Therefore, the reduction effect is more obvious than the oxidation effect. Furthermore, the UV-Vis absorption spectrum also proves this phenomenon: the oxidation product has a new red-shifted absorption peak (571 nm) and the reduction product has two new red-shifted absorption peaks (577 and 797 nm). We hope the present work can provide theoretical guidance for the search for high-performance nonlinear optical materials by using the redox effect.</p

Reply to “Comment on ‘How the Number and Location of Lithium Atoms Affect the First Hyperpolarizability of Graphene’”

Reply to “Comment on ‘How the Number and Location of Lithium Atoms Affect the First Hyperpolarizability of Graphene’

Pyramid-Like Au₂‑CNC under an External Electric Field: Charge Transfer, UV–Vis Absorption Spectra, and Nonlinear Optical Property

Due to the novel π-conjugated structure, carbon nanocone (CNC) has aroused the interest of the chemists. In the present work, we found that the replacement of two terminal carbon atoms by two gold atoms led to the obvious red shift of the absorption peak of Au2-CNC. Significantly, the latitudinal (y-axis) external electric field (EEF) can regulate the absorption peak, which is related to the second-order nonlinear optical response (βtot). The corresponding results are as follows: i. The intensity of the shoulder peak at about 300 nm increased mildly when EEF changed from 0 to −50 × 10–4 a.u., which caused the βtot values to decrease gradually. ii. A new broad absorption peak appeared at about 550 nm when EEF changed from 0 to 50 × 10–4 a.u., which generated increased βtot values. We hope that the present work can provide a fresh strategy to regulate and control the nonlinear optical property

Probing the Structure–Property Relationships of Na⁺···Cl^–@C₅₀N₅H₅ under the External Electric Field

Endohedral open-cage fullerenes are one of the attractive types of fullerenes due to their interesting electronic properties which make it potentially promising for applications in molecular electronics. In this paper, a novel structure of Na+···Cl–@C50N5H5 with Na+ inside the cavity and Cl– at the opening of the open-cage fullerene is designed to explore the chemical bonding and interaction between the open-cage fullerene system C50N5H5 and NaCl salt. Further, the directional migration of Na+ was achieved by applying an external electric field (EEF) along the X-axis. Notably, when the EEF ranges from −85 to −86 × 10–4 au, Na+ sharply approaches Cl– to regain its ionic bonding character. In addition, the Wiberg bond index, electron localization function topological analysis, and interaction energy (Eint) of the structure under the effect of the EEF also experienced a series of interesting changes. We hope that this work will provide a new strategy for the design of innovative materials for molecular electronics

Widening or Lengthening? Enhancing the First Hyperpolarizability of Tubiform Multilithium Salts

Very recently, tubiform multilithium salts have been investigated as new candidates for high-performance nonlinear optical (NLO) materials because of their large static first hyperpolarizability (β0) (J. Phys. Chem. C 2009, 113, 4984−4986). The interesting question of how to further enhance the β0 value of the multilithium salt, by widening or lengthening the tubiform cyclacene, is studied in this work. On one hand, the effect of widening on the β0 value of tubiform multilithium salts is investigated using Lin-[n]cyclacene (n = 5–8). We found that the β0 value (15497 au) of Li8-[8]cyclacene is 3 times larger than the 5028 au value of the Li5-[5]cyclacene, with the total number of carbon atoms increasing from 20 to 32. On the other hand, lengthening Li5-[5]cyclacene to form Li5–CNT (5,0) results in the dramatically enhanced β0 value of 146642 au, which is 29 times larger than the value for the Li5-[5]cyclacene, even though the total number of carbon atoms is increased only from 20 to 30. Further, the second harmonic generation (SHG) β(−2ω;ω,ω) and the electro-optical Pockels effect (EOPE) β(−ω;ω,0) increase with an increase in frequency (ω) from 0.0000 to 0.0200 au. Because cyclacenes have been proposed to be super-short single-walled carbon nanotubes, it is our expectation that this work could provide more useful information for the development of nonlinear optical nanomaterials

Phenalenyl π‑Dimer under the External Electric Field: Two-Electron/12-Center Bonding Breaking and Emergence of Electrostatic Interaction

Phenalenyl π-dimer (<b>PLY</b>_<b>2</b>) has recently attracted intensive research interest due to its unique structure and binding characteristics (two-electron<b>/</b>12-center bonding). The directional transfer of electron or electron pair under the external electric field can produce a new structure with interesting properties. In the present work, we investigate for the first time the effect of the external electric field along the main molecule axis on <b>PLY</b>_<b>2</b>. Two unpaired electrons between two layers are gradually shifted to the upper layer with increasing of the external electric field strength (<i>F</i>_ext): the weaker the two-electron<b>/</b>12-center bonding, the stronger the electrostatic interaction between two layers. Significantly, a small increment of <i>F</i>_ext makes a big difference: the interlayer distance in the <b>PLY</b>_<b>2</b> is sharply elongated from 3.241 Å (<i>F</i>_ext = 203 × 10^–4 au) to 3.485 Å (<i>F</i>_ext = 204 × 10^–4 au), which leads to the two-electron<b>/</b>12-center bonding breaking at 204 × 10^–4 au. Therefore, the <i>F</i>_ext = 204 × 10^–4 au is regarded as the critical electric field. In this case, the interaction between two layers in <b>PLY</b>_<b>2</b> is exclusively governed by the electrostatic interaction. Besides this, the effect of the external electric field brings some distinctive changes in its diradical character (<i>y</i>₀), the Wiberg bond index (WBI), the interaction energy (<i>E</i>_int), and the frontier molecular orbital (FMO) that can be used to explore the conversion between bonding and electrostatic interactions. This study can deepen the understanding for the effect of the external electric field on structures and electric properties for molecule and be an open a door for the discovery and development of new switching devices

Quantum Chemical Research on Structures, Linear and Nonlinear Optical Properties of the Li@<i>n</i>-Acenes Salt (<i>n</i> = 1, 2, 3, and 4)

On the basis of the n-acenes (n = 1, 2, 3 and 4), the α-Li@n-acenes and β-Li@n-acenes salts were selected to investigate how increasing the number n of conjugated benzenoid rings affects the linear and nonlinear optical responses. The α-Li@n-acenes and β-Li@n-acenes salts are obtained by a lithium atom substituting the α-H and β-H, respectively. In the present work, both ab initio (HF and MP2) and DFT (B3LYP, BhandHLYP, M05-2X, and CAM-B3LYP) methods are adopted to calculate the polarizability (α0) and first hyperpolarizability (βtot) of the α-Li@n-acenes and β-Li@n-acenes salts. MP2 results show that the α0 values of both classes of lithium salts increase with increasing number n of conjugated benzenoid rings. Interestingly, we found that the βtot values of α-Li@n-acenes and β-Li@n-acenes salts take on opposite trends: the βtot values of α-Li@n-acenes are decreasing slowly (2187 for α-Li@benzene > 1978 for α-Li@naphthalene > 1898 for α-Li@anthrecene > 1830 au for α-Li@tetracene) and inceasing remarkably (2738 for β-Li@naphthalene n-acenes. Furthermore, we found that the βtot values (2738−3314 au) of the β-Li@n-acenes are larger than those of the α-Li@n-acenes (1830−2187 au). On the other hand, comparing the results of different methods, the βtot values obtained by the M05-2X and CAM-B3LYP methods reproduce the polarizability and first hyperpolarizability of the α-Li@n-acenes and β-Li@n-acenes salts well, which test and verify the results of the MP2 method. Our present work may be beneficial to development of high-performance organic NLO optical materials

How the Number and Location of Lithium Atoms Affect the First Hyperpolarizability of Graphene

How do the number and location of lithium atoms affect the first hyperpolarizability (βtot) of graphene? In this paper, based on pentacene, a series of graphene (multi)lithium salts Lin@pentacene (n = 1, 2, 3, 4, 5, and 6) have been designed to answer this question. βtot obviously increases stepwise with an increase in the number of lithium atoms: 1369−1843 for Li@pentacence 2@pentacence 3@pentacence 4@pentacence 5@pentacence, which are much larger than pentacence. This pattern suggests that the lithium salt effect on the first hyperpolarizability is very large. Unexpectedly, when an additional lithium atom is doped into the graphene multilithium salt Li5@pentacence, which leads to Li6@pentacence, the βtot value dramatically increases to a value of 4 501 764 au with a remarkable increase of 302-fold in contrast to Li5@pentacence. On the other hand, when the number of lithium atoms is equal, the location of lithium atoms also affects the βtot value: the closer the lithium atoms are clustered, the larger the βtot value: for Li3@pentacence, 6933 au of system 10 E) are also obtained. The results show that ΔE decreases stepwise with an increase in the number of the lithium atoms, and ΔE of Li6@pentacence sharply decreases to 0.299 eV, which may explain the huge βtot value. This study may stimulate the search for new types of graphene NLO materials based on alkali metals for NLO application

Modulating the Charge Transfer of D–S–A Molecules: Structures and NLO Properties

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