First hyperpolarizability orientation in [70]PCBM isomers: A DFT study

Hyperpolarizability properties of [6,6]-phenyl C71 butyric acid methyl esters ([70]PCBM) isomers have been investigated, using full geometry optimization at B3LYP/6-311G(d,p) level of theory. Time-Dependent Density Functional Theory (TDDFT) calculations have been carried out to calculate the difference of dipole moment between the ground state and the excited state (Δμge) and the transition energies ΔE, and examine the nature of the electronic transitions. The two-state approximation employed to estimate the first hyperpolarizability. The dipole moment (μ), average polarizability (α), polarizability anisotropy (Δα), hyperpolarizability aligned along the direction of the dipole moment (βμ), and first hyperpolarizability (β) values of the isomers have been reported. Orientation of main direction of the first hyperpolarizability has been determined by calculation of the angle θ(μ,β) between the directions of the first hyperpolarizabilities and the permanent dipole moment of [70]PCBM isomers. First hyperpolarizability of chiral isomer was found to be 9.7 times the corresponding value for urea. Results indicate the potency of chiral [70]PCBM isomer for second-order nonlinear optical devices.