High hyperpolarizabilities of donor-π-acceptor-functionalized calix[4]arene derivatives by pre-organization of chromophores

A systematic investigation of the concept of pre-organization of nonlinear optical (NLO) active chromophoric groups in calix[4]arene derivatives and the influence on the absolute second-order nonlinear optical coefficients is reported. Several calix[4]arenes were synthesized by modification of the electron-withdrawing groups at the upper rim of the aromatic and extension of the conjugated π system of the preorganized chromophoric groups. Electrical field induced second harmonic generation (EFISH) experiments showed high μβ(0) values up to 1165·10^-48 esu. Compared with the corresponding reference compounds, enhancements of the μβ(0) values varying up to 2.5 times per chromophore were observed which proves the benefit of pre-organization of NLO-active units in a multi-chromophoric system. Another important advantage is that the increase in NLO activity observed for these systems is not accompanied with a shift of the absorption band to longer wavelengths exceeding 20 nm. This makes these calix[4]arene derivatives promising building blocks for the development of stable, NLO-active materials that are suitable for frequency doubling.