| Organic materials with large conjugate"Ï€"bridge possess strong inner-molecule charge transfer under suitable condition, which showed strong two-photon absorption (TPA) properties.(1) Six new multi-branched compounds with large conjugate"Ï€"bridge have been synthesized, abbreviated as P-B1,P-B3,P-T1,P-T3,P-W1 and P-W3.The photoluminescence properties and two-photon fluorescence of these compounds in different solvents, absorption spectra, fluorescence spectra on one-photon- and two-photon-excitation in solution were comparatively investigated. The results have been shown as follows:a The chromophores with strong fluorescence emission properties, the maximum fluorescence wavelengths are red shift in the same solution with the conjugated degree increasing.b Multi-branched compound shows strong two-photon absorption (TPA) properties, implying that the increase of molecular branch numbers play a major role in enhancement the molecular two-photon absorption.(2) In this study, the optical limiting property of the seven compounds, abbreviated as G1-OH,G2-CHO,G2-X,ST-G1,ST-G1.5,ST-G2 and ST-G1' were compared and summarized. The conclusions have been obtained as follows:a Excited state fluorescence lifetime and the laser-pumped time at the same level, there will apparently be reabsorbed in excited state.b With the increase in the number of branches, limiting the light was remarkably enhanced. The multi-branched sample liquor of ST-G2 has an optical limiting efficiency of 86%.c Increasing the concentration of the sample and the optical length will improve the optical limiting efficiency.
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