Two-photon absorption (TPA) properties of 1,3,5-tricyano-2,4,6-tris(styryl)benzene derivatives have been investigated. Comparison of the absorption and fluorescence spectra reveals that these compounds show large Stokes shifts, which increase gradually as the conjugation length increases. One-photon absorption and excitation spectra are similar except that the latter exhibit several peaks near λmax. It is also found that the one- and two-photon-induced fluorescence excitation spectra are quite similar, which indicates that the one- and two-photon allowed-excited states are the same. The peak TPA cross section values (δmax) measured with nanosecond pulses by the two-photon-induced fluorescence method are in the range (50-2620) × 10-50 cm4 s/photon. The δmax value increases as the donor strength and conjugation length increase. A linear relationship is observed between δmax and β, and this δ-β relationship is found to serve as a useful synthetic strategy for the design of novel TPA dyes with the octupolar structure.
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