A comprehensive theoretical study was carried out on a series of aryldimesityl borane (DMB) derivatives using Density Functional theory. Optimized geometries and electronic parameters like electron affinity, reorganization energy, frontiers molecular contours, polarizability and hyperpolarizability have been calculated by employing B3PW91/6-311++G (d, p) level of theory. Our results show that the Hammett function and geometrical parameters correlates well with the reorganization energies and hyperpolarizability for the series of DMB derivatives studied in this work. The orbital energy study reveals that the electron releasing substituents increase the LUMO energies and electron withdrawing substituents decrease the LUMO energies, reflecting the electron transport character of aryldimesityl borane derivatives. From frontier molecular orbitals diagram it is evident that mesityl rings act as the donor, while the phenylene and Boron atom appear as acceptors in these systems. The calculated hyperpolarizability of secondary amine derivative of DMB is 40 times higher than DMB (1). The electronic excitation contributions to the hyperpolarizability studied by using TDDFT calculation shows that hyperpolarizability correlates well with dipole moment in ground and excited state and excitation energy in terms of the two-level model. Thus the results of these calculations can be helpful in designing the DMB derivatives for efficient electron transport and nonlinear optical material by appropriate substitution with electron releasing or withdrawing substituents on phenyl ring of DMB system.

Calculations based on second-order Moller-Plesset and density functional theory (DFT) methods using different exchange and correlation functionals are performed on C 2 H 4 Nb organometallic complex for its hydrogen storage capacity. We found that this complex can store up to a maximum of 14 H 2 molecules using Becke-3 Lee-Yang-Parr (B3LYP)/LanL2DZ method, with a gravimetric H 2 uptake capacity of 18.92 wt% and average binding energy of 0.52 eV/H 2 . The evaluation of the temperature dependence of the Gibbs free energy change (DG) of H 2 adsorption process indicates that the adsorption of H 2 molecules is energetically favorable below 250 K using B3LYP (LanL2DZ) and PBEPBE (LanL2MB, LanL2DZ) level of theories. On the basis of the DFT descriptors, calculated at B3LYP (LanL2DZ) and B3PW91 (LanL2MB) level of theory, we found that the stability of the complex increases with increase in the number of H 2 molecules adsorbed by the complex.

This work involved the design of a new series of triarylaminehelicenes (TAH) with significant hole transport capacity and enhanced nonlinear optical response. The geometries, electronic properties and nonlinear response of TAH derivatives were studied using density functional theory at the B3PW91/6-311++G (2d, 2p) level. Charge transfer and nonlinear optical response were analyzed and correlated with modifications in geometry and energy levels. Calculations indicated that trivial changes in the torsional angle occur in TAH derivatives with electron-donating substituents as compared to those with electron-withdrawing substituents, resulting in lower reorganization energies for TAH derivatives 2-6. TAH derivatives with an -N(CH3)2 group have the greatest highest occupied molecular orbital (HOMO) level, and thus the least ionization potential, indicating significant hole transfer efficiency as compared to unsubstituted TAH. A decrease in the HOMO-LUMO gap occurs upon substitution with electron-releasing groups, whereas there is an increase in the case of -NO2, -COOH, and -CN TAH derivatives. Topological analysis of the HOMOs of the neutral molecules revealed that these orbitals are concentrated mainly in the helicene backbone, with an important contribution from fused phenyl rings, nitrogen atoms and carbonyl groups. However, the lowest unoccupied molecular orbitals (LUMO) are invariably constituted by fused phenyl rings without any contribution from the central nitrogen atom. Studying the effect of substitution on the nonlinear optical response of TAH derivatives, the calculated polarizability and hyperpolarizability at B3PW91/6-311++G (2d,2p) level of theory exhibited a prominent improvement as compared to unsubstituted TAH. Both electron-donating groups and electron-withdrawing groups result in a red shift in the electronic absorption bands of the substitution derivatives, in particular those with -N(CH3)2 and -NH2 groups.

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