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: The calculated reorganization energies for electron transport λ1, λ2 and λi are shown in Table 2 From Table 2, it is clear that the value of λi decrease both for DMB derivatives with electron releasing (2–7) and electron withdrawing (7–13) substituents as compared to non-substituted DMB (1), with exception of compound 8 and 9, where it slightly increases. The calculated values of inner sphere reorganization parameter (λi)for different derivatives largely correlates well with the order of structural changes from neutral to anionic species, reflected by the change in C18-B bond length, upon electron injection. The order of change in reorganization energy is much more uniform in case of electron releasing substituents, as compared to electron withdrawing substituents. In case of electron withdrawing group the reorganization energies follow the trend: _CN <_NO2<_Br <_COOH <_Cl <_F, with maximum for fluorine (0.214 eV) derivative which is, however, lower than to Alq3 (0.276 eV) [35], [51]. The smaller reorganisation energy value of DMB derivatives as compared Alq3 will benefit the charge carrier transport. For the DMB with the electron releasing group, the reorganization energies has the following order: _CH3> _C2H5>_OH>_OCH3>_NH2> _N(CH3)2. The Figure 4 shows a correlation of reorganization energies λ with Hammett parameter. In case of electron withdrawing groups the trend is irregular, floro shows large geometrical changes as compared to strong electron withdrawing substituents, such as _NO2, _COOH, and _CN comparable to those of un-substituted DMB(1), whereas electron releasing substituents show clear trend; the stronger (_NH2<_N(CH3)2) cause the DMB derivatives to undergo lesser geometry changes compared to weak electron releasing substituents. |
View Article: PubMed Central - PubMed
Affiliation: Department of Chemistry, University of Kashmir, Srinagar, Kashmir, India.