The β and γ nonlinear optical coefficients of substituted oligoacenes (1–10 rings) with the donors (D) groups –CH3, –CH2CH3, –CH2CH2CH3, –CH2CH2CH2CH3, –C(CH3)3, –CH3CHN(CH3)2, –N(CH3)2, –OCH3, –OCH2CH3, –OCH2CH2CH3, –OCH2CH2CH2CH3, –OC(CH3)3, and –OCHCH3N(CH3)2 and the acceptor (R) group –CHC(CN)2 is calculated by the AM1/TDHF method. A partial least squares regression analysis of electronic and structural parameters is performed to investigate their correlation with β and γ hyperpolarizabilities. It is found that the dipole moment, the HOMO–LUMO energy gap, the ionization potential, the number of π-electrons, and the number of rings in the bridge are parameters that significantly affect β and γ magnitudes. The dipole moment and the number of π-electrons are positively correlated with β values, while the HOMO–LUMO energy gap and the ionization potential are negatively correlated. Calculations indicate that the hyperpolarizabilities increase with the number of rings in the bridge and that the dimethylamine/dicyanoethenyl pair leads to the highest hyperpolarizabilities values. Optimization of β and γ is obtained through several substitution patterns of the oligoacenes. The present methodology shows that more extended systems containing two D/R pairs have high values of β and γ coefficients, which indicates that these systems can be employed in manufacturing nonlinear optics devices.
Marconi B. S. Costa, Ana E. de A. Machado, Antonio C. Pavão
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