Theoretical assessment of the nonlinear optical properties of substituted oligoacenes

Abstract

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.