  Small organic molecules with a {\pi}-conjugated system that consists of only
a few double or triple bonds can have significantly smaller optical excitation
energies when equipped with donor- and acceptor groups, which raises the
quantum limits to the molecular polarizabilities. As a consequence, third-order
nonlinear optical polarizabilities become orders of magnitude larger than those
of molecules of similar size without donor-acceptor substitution. This enables
strong third-order nonlinear optical effects (as high as 1000 times those of
silica glass) in dense, amorphous monolithic assemblies. These properties,
accompanied by the possibility of deposition from the vapor phase and of
electric-field poling at higher temperatures, make the resulting materials
competitive towards adding an active nonlinear optical or electro-optic
functionality to state-of-the-art integrated photonics platforms.
