Giant values obtained for first hyperpolarizabilities of methyl orange: a DFT investigation

Advances in photonics and optoelectronics depend on proposing new materials with well-defined nonlinear optics properties. Based on the foundations of density functional theory, this work presents a systematic investigation of linear and nonlinear optical properties of methyl orange, a well-known azo dye. Structural changes from alkaline to acidic structures drastically boost all investigated properties. For instance, the material dipole polarizability starts from an isotropic condition ( α iso > Δ α ) to an anisotropic behavior ( α iso < Δ α ). The first hyperpolarizabilities are also strongly tuned varying from 18.9 × 10 - 30 to 171.7 × 10 - 30 esu. A careful analysis of frontier molecular orbitals indicates proper wide-bandgap semiconductor energy gap (3.22 eV) and associates the highest hyperpolarizabilities to the lowest energy gap, which means semiconductor molecules with intense nonlinear optical activity.