Confined Lewis Pairs: Investigation of the X- →Si20 Interaction in Halogen-Encapsulating Silafulleranes

A joint theoretical and experimental study on 32 endohedral silafullerane derivatives [X@Si20 Y20 ]- (X=F-I; Y=F-I, H, Me, Et) andT h ${T_h }$ -[Cl@Si20 H12 Y8 ]- (Y=F-I) is presented. First, we evaluated the structure-determining template effect of Cl- in a systematic series of concave silapolyquinane model systems. Second, we investigated the X- →Si20 interaction energy (E int ${E_{{\rm{int}}} }$ ) as a function of X- and Y and found the largestE int ${E_{{\rm{int}}} }$ values for electron-withdrawing exohedral substituents Y. Given that X- ions can be considered as Lewis bases and empty Si20 Y20 clusters as Lewis acids, we classify our inseparable host-guest complexes [X@Si20 Y20 ]- as "confined Lewis pairs". Third, 35 Cl NMR spectroscopy proved to be highly diagnostic for an experimental assessment of the Cl- →Si20 interaction as the paramagnetic shielding and, in turn, δ ${\delta }$ (35 Cl) of the endohedral Cl- ion correlate inversely withE int ${E_{{\rm{int}}} }$ . Finally, we disclose the synthesis of [PPN][Cl@Si20 Y20 ] (Y=Me, Et, Br) and provide a thorough characterization of these new silafulleranes.

Designing Excess Electron Compounds by Substituting Alkali Metals to a Small and Versatile Tetracyclic Framework: A Theoretical Perspective

Organic compound-based nonlinear optical (NLO) materials have sparked a lot of attention due to their multitude of applications and shorter optical response times than those of inorganic NLO materials. In the present investigation, we designed exo-exo-tetracyclo[6.2.1.1^3,6.0^2,7]dodecane (TCD) derivatives, which were obtained by replacing H atoms of methylene bridge carbon with alkali metals (Li, Na, and K). It was observed that upon the substitution of alkali metals at bridging CH₂ carbon, absorption within the visible region occurred. Moving from 1 to 7 derivatives, the maximum absorption wavelength of the complexes exhibited a red shift. The designed molecules showed a high degree of intramolecular charge transfer (ICT) and excess electrons in nature, which were responsible for rapid optical response time and significant large molecular (hyper)polarizability. Calculated trends also inferred that the crucial transition energy decreased in order that also played a key role in the higher nonlinear optical response. Furthermore, to examine the effect of the structure/property relationship on the nonlinear optical properties of these investigated compounds (1-7), we calculated the density of state (DOS), transition density matrix (TDM), and frontier molecular orbitals (FMOs). The largest first static hyperpolarizability (β_tot) of TCD derivative 7 was 72059 au, which was 43 times greater than that of the prototype p-nitroaniline (β_tot = 1675 au).

Designing of gigantic first-order hyperpolarizability molecules via joining the promising organic fragments: a DFT study

A suitable substitution of carbazole with a π-spacer group like cyanoethynylethene offers exciting future opportunities in terms of smart nonlinear optical material. In the quest of better organic nonlinear optical material, we have designed a series of derivatives based on carbazole and cyanoethynylethene fragment combinations in a unique fashion by employing the density functional (DFT) methods. The calculated time-dependent density functional theory (TD-DFT) calculations infer that the gigantic first static hyperpolarizability (β_tot) values are due to a lower energy gap and higher transition dipole moment for the crucial electronic transition. Furthermore, to see the in-depth execution for enhanced second-order nonlinear optics and the structure property relationship on nonlinear optics (NLO) behavior, we have performed frontier molecular orbitals (FMO), density of state (DOS), and transition density matrix (TDM). Furthermore, CAM-B3LYP functional-based calculated results infer that the designed molecule 10 show the first static hyperpolarizability is 923.93 × 10^-30 esu which is 69 times larger than that of p-nitroaniline.

Ab initio study of medium sized boron-doped silicon clusters SinBm, n = 11-13, m = 1-3

The ground state and energetically low structures of neutral SinBm clusters, of medium size with n = 11-13, m = 1-3, are identified, presented and rationalized. Structures of the nanoclusters are predicted using density functional theory (DFT) and employing the HSE06 range-separated hybrid exchange-correlation functional. For these systems the functional is shown to offer systematic performance when benchmarked against high accuracy coupled-cluster CCSD(T) and compared to well known functionals used in the literature. Discrepancies for small size systems present in the literature are addressed and resolved. The structural evolution patterns of the clusters are discussed and common structural features (substructures) are identified. Cluster geometries are extensively searched via a particle swarm optimization algorithm alongside more traditional methodologies. In addition to the binding energies (that include zero-point energy corrections) of the structures, the optical gaps and UV/visible absorption spectra are reported, employing the CAM-B3LYP functional that was benchmarked against the high level EOM-CCSD level of theory. The computed infrared spectra are provided and discussed in length with respect to structural details. Their effectiveness as charge transfer units is examined. Optical gaps range between 1.4-2.5 eV, and are adjustable through the boron and silicon content of the clusters, which, along with the increased structural stability, offers promise for applications in optoelectronics.

Successive lithiation of acetylene, ethylene and benzene: a comprehensive computational study of large static second hyperpolarizability

This work is a revisit of the study of the electron correlation effect of lithium substitution on the second hyperpolarizability (10⁶ a.u.) of acetylene, ethylene and benzene. The large quenching of mean second hyperpolarizability has been addressed by CCSD calculations. The inclusion of triple excitation in the MP4 method generally overestimates second hyperpolarizability in comparison to the MP4SDQ method. The present CCSD γ_av value of C₆Li₆: 405 × 10⁴ a.u. obtained with a relatively larger basis set established the earlier prediction of Sadlej et al. [Phys. Chem. Phys. Chem., 2000, 2, 3393-3399] where degenerate non-dipolar transitions in low lying excited states play the crucial role. The successive lithiation results in gradual red shifting of transition energy leading to significant enhancement of second hyperpolarizability. Most of the chosen DFT functionals predict the correct qualitative trend of second hyperpolarizability. The quantitatively different results may be attributed to the case when the ground state wave function cannot be approximated by a single SD.

Static second hyperpolarizability of Λ shaped alkaline earth metal complexes

A number of Λ shaped complexes of alkaline earth metals Be , Mg and Ca with varying terminal groups have been considered for the theoretical study of their second hyperpolarizability. The chosen complexes are found to be sufficiently stable and for a chosen ligand the stability decreases in the order: Be -complex > Ca -complex > Mg -complex. The calculated results of second hyperpolarizability obtained at different DFT functionals for the 6-311++G(d,p) basis set are found to be fairly consistent. The Λ shaped ligands upon complex formation with metals lead to strong enhancement of second hyperpolarizability. The highest magnitude of cubic polarizability has been predicted for the metal complex having > C ( C 2 H 5)2 group. For a chosen ligand, the magnitude of second hyperpolarizability increases in the order Be -complex < Mg -complex < Ca -complex which is the order of increasing size and electropositive character of the metal. The variation of second hyperpolarizability among the investigated metal complexes has been explained in terms of the transition energy and transition moment associated with the most intense electronic transition.