Theoretical study of the second-order nonlinear optical properties of [N]helicenes and [N]phenylenes

The second-order nonlinear optical properties of helicenes and phenylenes were investigated at the time-dependent Hartee-Fock level using the Austin model 1 (AM1) semiempirical Hamiltonian. Antisymmetric isotropic component of the first hyperpolarizability and its projection on the dipole moment were determined for large helical systems and for their analogs substituted by donor/acceptor pairs. It was found that hyperpolarizability increases monotonically with the size of the system. It was shown that the large differences in the second-order NLO responses exhibit helical systems as a function of the chemical nature of the unit cell, the size of the helix and the position and nature of donor/acceptor substituents.