Electron transport and nonlinear optical properties of substituted aryldimesityl boranes: a DFT study.
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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.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.
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Affiliation: Department of Chemistry, University of Kashmir, Srinagar, Kashmir, India.
ABSTRACT
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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. |
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Mentions: We compare the selected geometry parameters with values of Î² of DMB derivatives. In molecules, with the releasing groups, the B-C18 bond length was observed to be minimum for dimethylamine derivative and maximum for ethyl derivative and follows the order 2<3<4â€Š=â€Š5<6<7, and the B-C2 and B-C10 bond length slightly decrease from dimethylamine derivative to ethyl derivative. In case of electron withdrawing groups, all the three B-C18, B-C2 and B-C10 bond lengths decreases but the maximum decreases appears in B-C18 bond [8â€Š=â€Š9>10>11â€Š=â€Š12>13], as substituted phenlyene ring is linked to boron through B-C18 bond. Probable reason may be extended- Ï€ conjugation improved by electron releasing groups. The well-known resonance and inductive effect [58], [59] may appropriately explain the relationship between donor-acceptor groups and the geometry. The increase in Ï€- conjugation due to +I (inductive) effect of electron releasing groups cause enhance in extent of resonance, results in geometrical modification of derivative on account of attachment of electron releasing substituent. The Hammett constant were correlated with hyperpolarizability. The plots of the Î² of DMB derivatives verses Ïƒ in figure 9 reveals that hyperpolarizability of DMB derivatives with electron releasing group decrease with increasing Ïƒ value. While as, in case of DMB derivatives with electron withdrawing groups, the Î² value increase with increase in Hammett value. The results fit a straight line with a correlation coefficient of 0.92 (or higher) for electron releasing groups, the other one has a correlation coefficient of 0.81 (or lower) for electron withdrawing groups. According to Ulman, inductive and resonance effects have contribution in Hammett substituent constant and both the effects are important to the molecules [58]. The donor group will easily push electrons towards the boron and remain itself slightly electron deficient. This situation affects the magnitude of dipole moments as well as hyperpolarizability. Thus, due to the presence of variety of functional groups (either having electron releasing or electron withdrawing abilities) affect the magnitude of static hyperpolarizability of DMBs. |
View Article: PubMed Central - PubMed
Affiliation: Department of Chemistry, University of Kashmir, Srinagar, Kashmir, India.