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Electron transport and nonlinear optical properties of substituted aryldimesityl boranes: a DFT study.

Pandith AH, Islam N - PLoS ONE (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Kashmir, Srinagar, Kashmir, India.

ABSTRACT
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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Calculated HOMO energies, LUMO energies of DMB derivatives (a) electron releasing substituents, (b) electron withdrawing substituents, together with the LUMO-HOMO gap at DFT/B3PW91/6-311++G (d,p) level of theory.
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pone-0114125-g005: Calculated HOMO energies, LUMO energies of DMB derivatives (a) electron releasing substituents, (b) electron withdrawing substituents, together with the LUMO-HOMO gap at DFT/B3PW91/6-311++G (d,p) level of theory.

Mentions: Electrical properties of molecular systems depend on the energies of levels allowed for electrons/holes and energy gap between these levels. The energies of the HOMO and LUMO levels used for the calculation of the energy gap were calculated using DFT employing B3PW91/6-311++G(d, p) level performed for isolated molecules (Table 3). It is clear from Table 3 that the electron releasing substituents(2–7) increase the LUMO energy of the DMB with increasing order of their electron donating behavior and, therefore, electron affinity of these DMB derivatives decreases in that order (Figure 5(a)). Whereas, the electron withdrawing groups (8–13) decrease the LUMO energy of the DMB with increasing order of their electron withdrawing character and, as a consequence, electron affinity of these DMB derivatives increases with increase in the electron withdrawing character of the substituents (Figure 5(b)). A similar trend is observed for the HOMO energies and ionization potential. Simply this behavior is explained by build of enhanced effect of π-conjugation due to electron-releasing environment created by electron rich substituents and decrease of electron densities by electron withdrawing substituents. However, it is observed that with electron releasing groups as substituents (2–7), the changes in the HOMO energies are larger than those of LUMO energies, whereas with electron withdrawing groups as substituents, the changes in LUMO energies are greater than HOMO energies. One important observation is that the HOMO-LUMO gap, ΔE(H-L), of the studied compounds decrease as compared to un-substituted DMB and this gap goes on decreasing with increase in the electron donating as well as electron withdrawing character of the substituents. Therefore, it is possible to tailor the HOMO-LUMO gap in such electron transport materials by rational variation of substitutions on the basis their position on the Hammett parameter (σ) scale. It was not possible to compare the calculated IP and EA with the experimental values due to lack of experimental data, however the plot of IP and EA correlated quite well with σ, which points out an obvious substitution effect on energy levels in the studied systems (Figure 6). The frontier molecular orbitals (FMOs) of all the systems are shown in Figure 7. It was observed that the highest occupied molecular orbitals (HOMOs) of the neutral molecules delocalize primarily over the two mesityl rings, whereas the lowest unoccupied molecular orbitals (LUMOs) localize largely on the Boron (B) atom and the phenylene of the DMB moiety, with a small contribution from electron releasing or withdrawing substituent. Thus, mesityl rings constitute the donor state, while the phenylene and B atom as the acceptors state in these systems. Compared to Alq3 [51] the LUMO is more delocalized than HOMO in case of DMB derivatives, indicating that the electron can easily move among the DMB molecule which will facilities enhanced electron transportation, particular in case of DMB derivatives with electron donating substituents. The HOMO-LUMO electronic transitions can be attributed to charge transfer from the two mesityl rings to the phenylene and the vacant pz of Boron atom. Thus, the minimization of the barrier for electron injection and transport can be achieved by proper adjustment of EA of given derivative.


Electron transport and nonlinear optical properties of substituted aryldimesityl boranes: a DFT study.

Pandith AH, Islam N - PLoS ONE (2014)

Calculated HOMO energies, LUMO energies of DMB derivatives (a) electron releasing substituents, (b) electron withdrawing substituents, together with the LUMO-HOMO gap at DFT/B3PW91/6-311++G (d,p) level of theory.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4257584&req=5

pone-0114125-g005: Calculated HOMO energies, LUMO energies of DMB derivatives (a) electron releasing substituents, (b) electron withdrawing substituents, together with the LUMO-HOMO gap at DFT/B3PW91/6-311++G (d,p) level of theory.
Mentions: Electrical properties of molecular systems depend on the energies of levels allowed for electrons/holes and energy gap between these levels. The energies of the HOMO and LUMO levels used for the calculation of the energy gap were calculated using DFT employing B3PW91/6-311++G(d, p) level performed for isolated molecules (Table 3). It is clear from Table 3 that the electron releasing substituents(2–7) increase the LUMO energy of the DMB with increasing order of their electron donating behavior and, therefore, electron affinity of these DMB derivatives decreases in that order (Figure 5(a)). Whereas, the electron withdrawing groups (8–13) decrease the LUMO energy of the DMB with increasing order of their electron withdrawing character and, as a consequence, electron affinity of these DMB derivatives increases with increase in the electron withdrawing character of the substituents (Figure 5(b)). A similar trend is observed for the HOMO energies and ionization potential. Simply this behavior is explained by build of enhanced effect of π-conjugation due to electron-releasing environment created by electron rich substituents and decrease of electron densities by electron withdrawing substituents. However, it is observed that with electron releasing groups as substituents (2–7), the changes in the HOMO energies are larger than those of LUMO energies, whereas with electron withdrawing groups as substituents, the changes in LUMO energies are greater than HOMO energies. One important observation is that the HOMO-LUMO gap, ΔE(H-L), of the studied compounds decrease as compared to un-substituted DMB and this gap goes on decreasing with increase in the electron donating as well as electron withdrawing character of the substituents. Therefore, it is possible to tailor the HOMO-LUMO gap in such electron transport materials by rational variation of substitutions on the basis their position on the Hammett parameter (σ) scale. It was not possible to compare the calculated IP and EA with the experimental values due to lack of experimental data, however the plot of IP and EA correlated quite well with σ, which points out an obvious substitution effect on energy levels in the studied systems (Figure 6). The frontier molecular orbitals (FMOs) of all the systems are shown in Figure 7. It was observed that the highest occupied molecular orbitals (HOMOs) of the neutral molecules delocalize primarily over the two mesityl rings, whereas the lowest unoccupied molecular orbitals (LUMOs) localize largely on the Boron (B) atom and the phenylene of the DMB moiety, with a small contribution from electron releasing or withdrawing substituent. Thus, mesityl rings constitute the donor state, while the phenylene and B atom as the acceptors state in these systems. Compared to Alq3 [51] the LUMO is more delocalized than HOMO in case of DMB derivatives, indicating that the electron can easily move among the DMB molecule which will facilities enhanced electron transportation, particular in case of DMB derivatives with electron donating substituents. The HOMO-LUMO electronic transitions can be attributed to charge transfer from the two mesityl rings to the phenylene and the vacant pz of Boron atom. Thus, the minimization of the barrier for electron injection and transport can be achieved by proper adjustment of EA of given derivative.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Kashmir, Srinagar, Kashmir, India.

ABSTRACT
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.

Show MeSH