Theoretical survey on the electronic, linear and nonlinear optical properties of substituted benzenes and polycondensed π -systems. A density functional theory study

Herein dipole moments, static and dynamic (hyper)polarizabilities, delocalization energies, distortions of the phenyl rings of the substituted benzenes are computed using density functional theory procedure. It is revealed that the biphenyl molecule exhibits the largest frequency-dependent second order hyperpolarizabilities. Furthermore, the application of an external electric field along the direction parallel to the molecular plane induces a considerable decrease in the energy of the unoccupied orbitals of biphenyl, resulting in more red- shifted virtual orbitals compared with benzene and the highest static second-order hyperpolarizability for the molecule. It is also found that when the two adjacent rings share only one carbon atom, high sigma and pi-electronic contributions to the second-order hyperpolarizabilities are expected. Interactions of the type pi* ->pi* with high delocalization energies are predicted for pyridine, nitrobenzene, chlorobenzene, bromobenzene, phenol, and benzoic acid. The quantum-mechanical calculations of the present work may provide theoretical insights into designing high (hyper)polarizability materials.