Nonlinear optical and two-photon absorption properties of 1,3,5-tricyano-2,4,6-tris(styryl)benzene-containing octupolar oligomers

Octupolar oligomers containing 2-12 molecules of 1,3,5-tricyano- 2,4,6-tris(styryl)benzene derivatives have been synthesized and their nonlinear optical and two-photon absorption (TPA) properties were determined. The β(0) values are in the range of (85- 1219) × 10^-30 esu and increase monotonically with the increasing number of the octupolar units within the molecule. The two-photon-induced fluorescence excitation spectra are quite similar to the single-photon absorption spectra except that the wavelength is doubled, indicating that the one- and two-photon allowed excited states are the same. The peak TPA cross-section values (δ_max) measured with nanosecond pulses by the two-photon-induced fluorescence method are in the range (3010-62930) × 10^-50 cm⁴s photon^-1. The δ_max increases as the number of the octupolar units in the molecules increases. A linear relationship is observed between δ_max and β, and this δ-β relationship serves as a useful design strategy for the synthesis of novel octupolar oligomers and polymers with large TPA and β.