Electronic And Nonlinear Optical Features of Inorganic Ga12N12 Nanocage Decorated With Alkali Metals (Li, Na and K)

The effect of alkali metals (Li, Na and K) interaction on the nonlinear optical response (NLO) of Ga12N12 nanocage has been performed using density functional theory (DFT) calculations. The results show that the exo-M@Ga12N12 structures are energetically favorable with negative interaction energies in the range of ‒1.50 to ‒2.28 eV. The electronic properties of decorated structures are strongly sensitive to interaction with the alkali metals. The HOMO-LUMO gap of Ga12N12 is reduced by about 70% due to the decoration with alkali metals. It is obtained that the adsorption of alkali metals over the tetragonal ring of Ga12N12 nanocage remarkably enhances the first hyperpolarizability up to 6.5×104 au. The results display that decorating Ga12N12 nanocage with alkali metals can be introduced it as a novel inorganic nanomaterial with significant NLO properties.

Exploration of Nonlinear Optical Enhancement and Interesting Optical Behavior with Pyrene Moiety as the Conjugated Donor and Efficient Modification in Acceptor Moieties

Herein, a series of new pyrene based hexylcyanoacetate derivatives (HPPC1-HPPC8) with A–π–D–π–D configuration were designed by end-capped modeling of non-fullerene acceptors on the structure of reference compound named dihexyl 3,3'-(pyrene-1,6-diylbis(4,1-phenylene))(2E,2'E)-bis(2-cyanoacrylate) HPPCR. Quantum chemical calculations of HPPCR and HPPC1-HPPC8 were accomplished at M06/6-31G(d, p) level. The stability of molecules due to the strongest hyper conjugative interactions in HPPCR and HPPC1-HPPC8 was estimated through NBO study. Interestingly, HOMO-LUMO band-gap of HPPC1-HPPC8 was found smaller than HPPCR which resulted in large NLO response. Among all the investigated compounds HPPC7 showed the larger NLO response due to the presence of four cyanide (CN) groups which strengthens the bridge conjugation, and its band gap was found to be 2.11eV, smaller as compared to band gap of HPPCR (3.225 eV). The absorption spectra of HPPC1-HPPC8 compounds showed maximum absorption wavelengths (483–707 nm) than HPPCR (471.764nm). The designed compounds showed high NLO response than HPPCR. Amazingly, highest amplitude of linear polarizability < α>, first hyperpolarizability (βtotal) and second hyperpolarizability < γ > for HPPC7 were achieved to be 1331.191, 200112.2 and 4.131 ×107 (a.u), respectively. NLO response showed that the HPPC1-HPPC8 might be potential candidates for NLO applications.

Density Functional Theory Study of Substitution Effects on the Second-Order Nonlinear Optical Properties of Lindquist-Type Organo-Imido Polyoxometalates

Density functional theory and time-dependent density functional theory have been enacted to investigate the effects of donor and acceptor on the first hyperpolarizability of Lindquist-type organo-imido polyoxometalates (POMs). These calculations employ a range-separated hybrid exchange-correlation functional (ωB97X-D), account for solvent effects using the implicit polarizable continuum model, and analyze the first hyperpolarizabilities by using the two-state approximation. They highlight the beneficial role of strong donors as well as of π-conjugated spacers (CH=CH rather than C≡C) on the first hyperpolarizabilities. Analysis based on the unit sphere representation confirms the one-dimensional push-pull π-conjugated character of the POMs substituted by donor groups and the corresponding value of the depolarization ratios close to 5. Furthermore, the use of the two-state approximation is demonstrated to be suitable for explaining the origin of the variations of the first hyperpolarizabilities as a function of the characteristics of a unique low-energy charge-transfer excited state and to attribute most of the first hyperpolarizability changes to the difference of dipole moment between the ground and that charge-transfer excited state.

Exploration of Nonlinear Optical Properties of Triphenylamine-Dicyanovinylene Coexisting Donor-π-Acceptor Architecture by the Modification of π-Conjugated Linker

High-tech electronic, optics, and storage devices require organic compounds with nonlinear optical (NLO) properties. This study designed D-π-A based dyes with donor triphenylamine (TPA) and acceptor dicyanovinylene (DCV) species by structurally modifying π-conjugated linkers. Our density functional theory (DFT) computations analyzed the impact of structural variations on the nonlinear optical (NLO) response of newly designed dyes. The B3LYP/6-31G(d,p) level determined the quantic chemical insights: frontier molecular orbital (FMOs), natural bond orbitals (NBOs), and nonlinear optical (NLO) properties of the designed dyes (DPTM-1 to DPTM-12). UV-Vis analysis based on the TD-DFT/CAM-B3LYP/6-311+G(d,p) level explored the optoelectronic properties. DPTM-1 and DPTM-5 showed the highest red-shifted absorption band at 519 and 506 nm. NBO analysis shows that DPTM-1 to DPTM-12 dyes have positive values for all donors (D) and π-spacers but negative values for acceptors (A). The π-spacers act as a conveyer between donor and acceptor moieties; thus, electrons were transferred smoothly from D to A units, which resulted in a charge separation state. Our calculations show the extent of NLO response in terms of electronic transitions, polarizability &lt;α&gt;, and first hyperpolarizability (β) values. The highest value of βtotal was 110,509.23 a.u. manifested in DPTM-6 due to 2,5-dimethyloxazole as a second π-linker, twice that of R (66,275.95 a.u.). Also, DPTM-6 and DPTM-8 exhibit the lowest energy band gap of 2.06 and 2.04 eV, respectively. In short, all DPTM-1 to DPTM-12 dyes manifested maximum absorption, lowest energy band gap, greater charge transfer from donor to the acceptor, and better first hyperpolarizability values as compared to the R and showed good NLO response. The present work represents new compounds with remarkable NLO properties and their applications in modern high-tech devices.

Hyperpolarizability of Water at the Air-Vapor Interface: Numerical Modeling Questions Standard Experimental Approximations

<div>In this article, we investigate the molecular first hyperpolarizability of water molecules nearby the liquid-vapor interface. The hyperpolarizability of each molecule is calculated at the quantum level within an explicit, inhomogeneous electrostatic embedding. We report that the average molecular first hyperpolarizability tensor depends on the distance relative to the interface, but it practically respects the Kleinman symmetry everywhere in the liquid. </div><div>Within this numerical approach, based on the dipolar approximation, the water layer contributing to the Surface Second Harmonic Generation (S-SHG) intensity is less than a nanometer. We show that within this interfacial layer, the common assumption considering a single, constant hyperpolarizability for all water molecules is not supported by our data: hyperpolarizability fluctuations are expected to impact the S-SHG intensity. These results represent a step forward the molecular interpretation of experimental S-SHG signal of aqueous interfaces. </div>

Hyperpolarizability of Water at the Air-Vapor Interface: Numerical Modeling Questions Standard Experimental Approximations

<div>In this article, we investigate the molecular first hyperpolarizability of water molecules nearby the liquid-vapor interface. The hyperpolarizability of each molecule is calculated at the quantum level within an explicit, inhomogeneous electrostatic embedding. We report that the average molecular first hyperpolarizability tensor depends on the distance relative to the interface, but it practically respects the Kleinman symmetry everywhere in the liquid. </div><div>Within this numerical approach, based on the dipolar approximation, the water layer contributing to the Surface Second Harmonic Generation (S-SHG) intensity is less than a nanometer. We show that within this interfacial layer, the common assumption considering a single, constant hyperpolarizability for all water molecules is not supported by our data: hyperpolarizability fluctuations are expected to impact the S-SHG intensity. These results represent a step forward the molecular interpretation of experimental S-SHG signal of aqueous interfaces. </div>