Exploring Li4N and Li4O superalkalis as efficient dopants for the Al12N12 nanocage to design high performance nonlinear optical materials with high thermodynamic stability

Theoretically designed M@diaza[2.2.2]cryptand complexes: the role of non-covalent interactions in promoting NLO properties of organic electrides

Organic excess electron compounds with significant nonlinear optical (NLO) properties are widely employed in optoelectronic applications. Herein, single-alkali metals with diaza[2.2.2] cryptand (M@crypt,M=Li, Na, and K) are investigated for optoelectronic and NLO properties by using the density functional theory. Thermodynamic and kinetic stabilities of present complexes are computed through interaction energy (Eint) and ab-initio molecular dynamic (AIMD) simulations. M@crypt complexes carry excess electrons and mimic molecular electrides. Quantum theory of atoms in molecules (QTAIM) analysis and reduced density gradient (RDG) spectra demonstrate the roles of the weak van der Waals (vdW) interactions between metal and complexant. The remarkable hyperpolarizability (βo) value up to 1.41 × 106 au may be credited to the presence of loosely bound excess electrons. The hyper Rayleigh scattering hyperpolarizability (βHRS) is recorded up to 1.31 × 106 au for the K@crypt. Furthermore, frequency-dependent first-order and second-order hyperpolarizability is more prominent at the applied frequency of ω = 0.042823 au. The electron localizing function (ELF) and localized orbital locator (LOL) analysis further disclose the nature of interaction between alkali metal and complexant. The TD-DFT method is adopted to get excited state parameters and absorbance properties. An electron density difference map (EDDM) is exploited to evaluate the orbital contributions in excited states. Hence, the studied electride may become a promising candidate for NLO materials. We anticipate that the present work will provide insight into further development of molecular electride for optoelectronic applications.

Enhancing NLO performance by utilizing tyrian purple dye as donor moiety in organic DSSCs with end capped acceptors: A theoretical study

A series of new organic dyes (T1-T6) with nonfullerene acceptors have been theoretically designed around the chemical structure of tyrian purple (T) natural dye. For their ground state energy parameters, all the molecular geometries of those dyes were optimized by density functional theory (DFT) at its Becke, 3-parameter, Lee-Yang-Parr (B3LYP) level of theory with 6-31G+(d,p) basis sets. When benchmarking against several long range and range separated levels of theory, the Coulomb attenuated B3LYP (CAM-B3LYP) produced most accurate absorption maxima (λmax) value to that of T so it was further employed for further Time dependent DFT (TD-DFT) calculations. Frontier molecular orbitals (FMOs) with natural bond orbital (NBO) studies were used to study their intra molecular charge transfer (ICT). All of the dyes had their energy gaps (Eg) values between their FMOs to range around 0.96-3.39 eV, whereas the starting reference dye had an Eg of 1.30 eV. Their ionization potential (IP) values were ranged to be 3.07-7.25 eV which indicated their nature to loss electrons. The λ max in chloroform was marginally red-shifted with a value 600-625 from T (580 nm). The dye T6 showed its highest linear polarizability (<α>), and first and second order hyperpolarizabilities (β and γ). The synthetic experts can find the present research to design finest NLO materials for current and future uses.

Mixed superalkalis are a better choice than pure superalkalis for B12N12 nanocages to design high-performance nonlinear optical materials

Mixed superalkali clusters are a source of excess electrons, as their vertical ionization energies (2.81-3.36 eV) are much lower than those of alkali metals (even cesium (∼3.85 eV)) and the superalkali Li₃O (3.42 eV). In the present work, the geometric, electronic, and nonlinear optical (NLO) properties of mixed superalkali cluster-doped B₁₂N₁₂ nanocages are studied theoretically. All complexes, A-G, have very high interaction energies (-98.02 to -123.13 kcal mol^-1) and are thermodynamically stable when compared to previously reported Li₃O@B₁₂N₁₂ (-92.71 kcal mol^-1). The designed complexes have smaller HOMO-LUMO energy gaps (3.36-4.27 eV) than pristine B₁₂N₁₂ (11.13 eV). Charge transfer in the complexes is studied through natural population analysis and non-bonding interactions are evaluated through quantum theory of atoms in molecules (QTAIM) and non-covalent interaction analyses. These complexes have absorption maxima (1076-1486 nm) in the near-infrared region (NIR) and they are transparent in the UV region. The first hyperpolarizability of complex C is 1.7 × 10⁷ au, which is much higher than the value of 3.7 × 10⁴ au for a pure Li₃O superalkali-doped B₁₂N₁₂ complex calculated at the same level of theory, as reported by Sun et al. (Dalton Trans., 2016, 45, 7500-7509). The large second hyperpolarizability values also reflect the enhanced nonlinear optical response. The best computed values for the electro-optical Pockels effect, second harmonic generation, and hyper-Rayleigh scattering are 3.29 × 10¹⁰ au, 1.17 × 10¹⁰ au, and 6.71 × 10⁶ au, respectively. Furthermore, the electro-optic dc-Kerr effect and electric-field-induced second harmonic generation have maximum values of 3.96 × 10¹¹ au and 3.46 × 10¹⁰ au at 1064 nm. There are enhancements in the quadratic nonlinear refractive index (n₂) values for complexes A-G, with a highest n₂ value of 3.35 × 10^-8 cm² W^-1 at 1064 nm. These results suggest that mixed-superalkali-doped B₁₂N₁₂ nanoclusters are potential candidates when designing high-performance NLO materials.

Demonstrating the Potential of Alkali Metal-Doped Cyclic C6O6Li6 Organometallics as Electrides and High-Performance NLO Materials

In this report, the geometric and electronic properties and static and dynamic hyperpolarizabilities of alkali metal-doped C6O6Li6 organometallics are analyzed via density functional theory methods. The thermal stability of the considered complexes is examined through interaction energy (E int) calculations. Doping of alkali metal derives diffuse excess electrons, which generate the electride characteristics in the respective systems (electrons@complexant, e-@M@C6O6Li6, M = Li, Na, and K). The electronic density shifting is also supported by natural bond orbital charge analysis. These electrides are further investigated for their nonlinear optical (NLO) responses through static and dynamic hyperpolarizability analyses. The potassium-doped C6O6Li6 (K@C6O6Li6) complex has high values of second- (βtot = 2.9 × 105 au) and third-order NLO responses (γtot = 1.6 × 108 au) along with a high refractive index at 1064 nm, indicating that the NLO response of the corresponding complex increases at a higher wavelength. UV-vis absorption analysis is used to confirm the electronic excitations, which occur from the metal toward C6O6Li6. We assume that these newly designed organometallic electrides can be used in optical and optoelectronic fields for achieving better second-harmonic-generation-based NLO materials.