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Density functional studies of the dipole polarizabilities of the linear polyacenes benzene through nonacene

100%

Hinchliffe A. , Nikolaidi B. , Soscún Machado H.

Open Chemistry

2005

tom 3

nr 2

361-369

We report Ab Initio studies of the electric dipole polarizability of the linear polyacene series benzene through nonacene. A number of Ab Initio studies were done at different levels of theory for benzene, with all remaining Ab Initio calculations being at the B3LYP/6-311G(2d, 1p)//B3LYP/6-311+G(2d, 1p) level of theory. We find that the NN tensor component shows a constant increment of 20 atomic units per ring. AM1 and QSAR-quality empirical calculations show poor absolute agreement with the Ab Initio results but given excellent statistical correlation coefficients with the Ab Initio values. This implies that the results of such cheaper calculations can be suitably scaled for predictive purposes.

Enhancement of molecular polarizabilities by the push-pull mechanism; a DFT study of substituted benzene, furan, thiophene and related molecules

80%

Hinchliffe A. , Mkadmh A. , Nikolaidi B. , Soscún H. , Abu-Awwad F.

Open Chemistry

2006

tom 4

nr 4

743-759

We report Density Functional Theory (DFT) studies of the dipole polarizabilities of benzene, furan and thiophene together with a number of substituted and related systems. All geometries were optimized (and characterized) at the B3LYP/6-311g(2d,1p) level of theory and polarizabilities then calculated with B3LYP/6-311++G(2d,1p). For the R-ring systems we find group polarizabilities in the order R = NO2 ∼ OCH3 ∼ CN ∼ CHO > NH2 > OH > H = 0. For systems R-ring-R, 〈α〉 differs little from the additivity model, with small positive and negative increments. For systems D-ring-A (where D and A are deactivating and activating groups) we find a positive enhancement to 〈α〉 over and above the value expected on the basis of pure additivity for all pairs A and D studied. This enhancement can be increased greatly by extending the length of the conjugated chain to D-ring-CH=CH-ring-A and D-ring-N=N-ring-A systems. Empirical models of polarizability such as AM1 agree badly with the DFT calculations in an absolute sense but give excellent statistical correlation coefficients. Calculated 〈α〉’s also agree well in a statistical sense with the molecular volumes calculated from molecular mechanics force fields Analysis of the results in terms of the π electrons alone is not satisfactory.