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Theoretical investigation on redox-switchable second-order nonlinear optical responses of push-pull Cp*CoEt2C2B4H3-expanded (metallo)porphyrins.

The second‐order nonlinear optical (NLO) properties of the Cp*Co(C2H5)2C2B4H3‐expanded (metallo)porphyrins (Cp* = C5Me5) have been investigated by using ab inito RHF and density functional theory (DFT) methods. The investigation shows that the compound with expand porphyrin possesses remarkable large molecular hyperpolarizability βtot value, ∼414.1 × 10−30 esu (at LC‐ωPBE level), and might be an excellent second‐order NLO material. From the character of charge transfer (CT) transition, it indicates that the −Cp*Co(C2H5)2C2B4H3 acts as an electron donor in this kind of systems. As a result of the redox behavior on expanded (metallo)porphyrin, the redox switching character of the NLO responses for the systems 2a–4a has also been studied. The results show that the βtot values of reduced forms are larger than that of neutral ones. Furthermore, the time‐dependent DFT calculation illustrates that reduced forms have a significant difference on the CT patterns versus neutral ones. The present investigation provides insight into the comparison with DFT results on estimating first hyperpolarizability and the NLO properties of the series of push–pull compounds.

Strategy for enhancing second-order nonlinear optical properties of the Pt(II) dithienylethene complexes: substituent effect, π-conjugated influence, and photoisomerization switch.

The second-order nonlinear optical (NLO) properties of a series of Pt(II) dithienylethene (DTE) complexes possessing the reversible photochromic behavior have been investigated by density functional theory (DFT) combined with the analytic derivatives method. The results show that the calculated static first hyperpolarizabilities (βtot) of the open-ring and closed-ring systems significantly increase in the range of 2.1-4.5 times through strengthening of the electron-withdrawing ability of the substituent R (R = H, CF3, NO2) and an increase of the number of thiophene rings. Moreover, there is a large enhancement of the βtot values from the open-ring systems to the corresponding closed-ring systems. This efficient enhancement is attributed to the better delocalization of the π-electron system, the more obvious degree of charge transfer, and the larger f(os)/E(gm)(3) (f(os) is the oscillator strength, and E(gm) is the transition energy between the ground and the excited states) values in the closed forms according to the bond length alternation (BLA) and time-dependent density functional theory (TDDFT) calculations. In addition, the dispersion has less influence on the frequency-dependent first hyperpolarizabilities (βtot(ω)) of the studied systems at the low-frequency area ω (0.000-0.040 au). Our present work would be beneficial for further theoretical and experimental studies on large second-order NLO responses of metal complexes.

Theoretical investigation on electronic structure and second-order nonlinear optical properties of novel hexamolybdate-organoimido-(car)borane hybrid.

We report a theoretical study based on density functional theory (DFT) on the geometric and electronic structure, linear optical and second-order nonlinear optical properties of a series of new inorganic-organic hybrid hexamolybdate-organoimido-(car)boranes. By the incorporation of borane/carborane at the end of the phenyl ring of the organoimido segment, the studied systems show excellent nonlinear optical (NLO) response than the organoimido-substituted hexamolybdate. The computed static first hyperpolarizability β(vec) value of [Mo(6)O(18)(NC(8)H(8))(B(12)H(11))](4-) (II) is largest, -167.2 × 10(-30) esu, and a higher β(vec) value of [Mo(6)O(18)(NC(8)H(8))(C(2)B(10)H(11))](2-) (III-2p) is 58.6 × 10(-30) esu. Moreover, the time-dependent (TD)DFT calculation illustrates that the maximum absorption, which is helpful for the large NLO responses, is mainly assigned to the charge transfer (CT) from (car)borane and organoimido segment to the hexamolybdate cluster. The density of density (DOS) calculations further illustrate the excitation from valence orbitals of boron atoms to that of Mo and O atoms in hexamolybdate can be responsible for larger NLO responses. The linear and nonlinear optical properties of species III both vary with the position of the vertex on the carborane. Furthermore, the order of the β(vec) values is consistent with the bathochromic shift of the maximum absorption for our studied systems, and the studied systems show a wider transparency range extending into the entire visible and infrared (IR) region.

Theoretical exploration to second-order nonlinear optical properties of new hybrid complexes via coordination interaction between (metallo)porphyrin and [MSiW11O39]3− (M = NbV or VV) polyoxometalates

The second-order nonlinear optical (NLO) properties of hybrid complexes via coordination interaction between porphyrin and Keggin-type polyoxometalates (POMs) α-[MSiW11O39](3-) (M=Nb(V) or V(V)) are investigated by time-dependent density functional theory (TDDFT). The calculated results show that this kind of organic-inorganic hybrid complexes possesses remarkably large molecular second-order NLO polarizability, especially for the ZnP3P-C≡C-4-Py-[VSiW11O39](3-) (complex 4), which has a computed β0 value of 261,410 a.u. and might be an excellent second-order NLO material. The effects of substituted metal atom (M), metalloporphyrin, and π-conjugation on NLO response are analyzed, the substituted metal atom (M) with a large electronegativity, the metalloporphyrin, and the lengthening of π-conjugation are helpful in enhancing the optical nonlinearity of these systems, which reveal the general rules to design the complexes with large optical nonlinearities. Furthermore, the solvent effect largely affects the first-order hyperpolarizability of the complex, it implies that the second-order polarizabilities increased with the increase of the solvent in polarity.

Enhancement of second-order nonlinear optical response in boron nitride nanocone: Li-doped effect.

The unusual properties of Li-doped boron nitride nanomaterials have been paid further attention due to their wide applications in many promising fields. Here, density functional theory (DFT) calculations have been carried out to investigate the second-order nonlinear optical (NLO) properties of boron nitride nanocone (BNNC) and its Li-doped BNNC derivatives. The natural bond orbital charge, electron location function, localized orbital locator and frontier molecular orbital analysis offer further insights into the electron density of the Li-doped BNNC derivatives. The electron density is effectively bounded by the Li atom and its neighboring B atoms. The Li-doped BNNC molecules exhibit large static first hyperpolarizabilities (β(tot)) up to 1.19×10³ a.u. for Li@2N-BNNC, 5.05×10³ a.u. for Li@2B-BNNC, and 1.08×10³ a.u. for Li@BN-BNNC, which are significantly larger than that of the non-doped BNNC (1.07×10² a.u.). The further investigations show that there are clearly dependencies of the first hyperpolarizabilities on the transition energies and oscillator strengths. Moreover, time-dependent DFT results show that the charge transfer from BNNC to Li atom becomes more pronounced as doping the Li atom to BNNC. It is also found that the frequency-dependent effect on the first hyperpolarizabilities is weak, which may be beneficial to experimentalists for designing Li-doped BNNC molecules with large NLO responses.

Theoretical insights into [PMo12O40](3-) grafted on single-walled carbon nanotubes.

Nano-hybrid materials based on a combination of polyoxometalate (POM) clusters and single-walled carbon nanotubes (SWNT) exhibit a great interesting application in molecular cluster batteries. The interactions between POM and SWNT and their detailed electronic properties have been investigated by employing first-principles calculations. Various models were constructed to study the geometries, interactions (binding sites and energies), and charge transfer behavior. Analysis of charge distributions reveals two different charge transfer characteristic depending on the type of POM interaction with SWNT. The simulation provides insight into the optimal structures in lieu of interfacial stability. Finally, the implications of these results for understanding the properties of molecular cluster batteries are discussed.

TDDFT studies on the determination of the absolute configurations and chiroptical properties of Strandberg-type polyoxometalates.

The electronic circular dichroism (ECD) and UV-visible absorption (UV-vis) spectra of Strandberg-type polyoxometalates (POMs) (R, R)-[(R*PO3)2M5O15](2-) (R* = CH3CH(NH3), (M = Mo, W)) have been explored using the time-dependent density functional theory (TDDFT) method. It demonstrates that the absolute configurations of chiral systems can be determined by chiroptical spectroscopic methods combined with DFT calculations. The calculated ECD spectra of the Strandberg-type molybdate were produced over the range of 3.3-6.5 eV, which are generally in agreement with the experimental spectra. In addition, the ECD spectra of (R, R)-[(R*PO3)2W5O15](2-) (R* = CH3CH(NH3)) were produced over the range of 4.5-8.5 eV. The Beckes half-and-half hybrid exchange-correlation functional (BHandHLYP) with the HF exchange fraction to 55% hybrid functional was found to well predict the excitation energies of studied systems. The origins of the ECD bands of two systems are mainly ascribed to charge-transfer (CT) transitions from oxygen atoms to metal atoms in polyanion. The results suggest that the polyanion are chiroptical chromophores. The polyanion plays a role as an optically active chromophore and contribute to the absorptions of ECD spectra. The difference of the UV-vis/ECD spectra between two systems shows that the transition metal atom significantly influences on the chiroptical properties of the studied Strandberg-type POMs.

Interlayer charge-transfer in impacting the second hyperpolarizabilities: Radical and cation species of hexathiophenalenylium and its nitro dimers

Hexathiophenalenylium (HTPLY) has gained increasing attention for its interesting and potentially useful optical properties as a result of the enhancement in spin delocalization and charge-transfer of phenalenyl radicals, occasioned by the attachment of successive three disulfide linkages. Herein, we performed density functional theory to calculate the binding interactions, electronic absorption spectra and the second hyperpolarizabilities of cation and radical dimers of HTPLY and its nitro derivatives. It is found that the equilibrium structures of the π dimers at fully staggered position are most stable. Among these π dimers, radical dimers exhibit stronger binding interactions with respect to cation dimers. In addition, obvious red shifts in electronic spectra of radical dimers are dependent on the large interlayer charge-transfers. More importantly, radical dimers [4]dim3 and [5]dim1 exhibit a significant increase in the second hyperpolarizabilities as compared to cation dimers, which is due to lower excitation energies and larger interlayer charge-transfers. We believe that the results presented in this article shall provide important evidence for the large interlayer charge-transfers in enhancing the NLO properties of the π dimers.

Theoretical investigation on switchable second-order nonlinear optical (NLO) properties of novel cyclopentadienylcobalt linear [4]phenylene complexes

AbstractAs a kind of novel organometallic complexes, the cyclopentadienylcobalt (CpCo) linear [4]phenylene complexes (4 = number of benzene rings) display efficient switchable nonlinear optical (NLO) response when CpCo reversibly migrates along the linear [4]phenylene triggered by heating or lighting. In this paper, the second-order NLO properties for CpCo linear [4]phenylene complexes were calculated by using the density functional theory (DFT) methods with four functionals. All of the functionals yield the same order of βtot values: 1<2<4<3. The effect of solvent on second-order NLO properties has been studied using polarized continuum model (PCM) in the tetrahydrofuran (THF) solution. The solvent leads to a slight enhancement of the NLO responses for the studied complexes relevant to their NLO responses in vacuo. The electronic absorption spectra were investigated by the TDDFT methods. The TDDFT calculations indicate that the maximum absorption peaks of complexes 2–4 in the near-infrared spectrum area show the bathochromic shift together with a decreasing intensity compared to complex 1. We have also found that the cobalt (Co) atom acts as a donor in all the organometallic complexes and the d → π* and π → π* charge transfer (CT) transitions contribute to the enhancement of second-order NLO response. Furthermore, two experimentally existing complexes 1 and 3 are found to have a large difference in βtot values. It is our expectation that this difference may stimulate the search for a new type of switchable NLO material based on CpCo linear [4]phenylene complexes. FigureThe second-order NLO properties of the cyclopentadienylcobalt (CpCo) linear [4]phenylene complexes were investigated by density functional theory (DFT) method, and complexes 1 and 3 display switchable NLO responses.

Theoretical studies on the photoisomerization-switchable second-order nonlinear optical responses of DTE-linked polyoxometalate derivatives.

The switchable second-order nonlinear optical (NLO) responses of the photoisomerized chromophore dithienylperfluorocyclopentene (DTE) derivatives, organic-inorganic systems of Lindqvist-type [Mo₆O₁₉]²⁻, have been investigated by tuning open-ring and the closed-ring form. In the present paper, we performed density functional theory (DFT) combined with finite field (FF) methods to calculate the second-order NLO coefficients for these organic-inorganic compounds. The calculations with three functionals (B3LYP/CAM-B3LYP/LC-BLYP) confirm the switching behavior on NLO properties by the photoisomerization reaction. The β(tot) value of system 2c (closed-ring form) is 10 times larger than that of its open-ring form (system 2o). And the other two pairs of systems also show good tuning properties. The ampliative ratio on second-order NLO coefficients between systems 2o and 2c (β(2c)/β(2o)) is 13 times as large as that of DTE (β(DTEc)/β(DTEo)). It suggests that introduction of [Mo₆O₁₉]²⁻ and organic groups to the DTE monomer effectively improve the conversion ratio of second-order NLO coefficients between the open-ring and closed-ring forms.