Synthesis, two-photon absorption and optical limiting properties of multi-branched styryl derivatives based on...

Five new multi-branched two-photon absorption triazine chromophores (T1-T5) with different donor strength, conjugation length, and direction of charge transfer have been designed and synthesized. The one-photon fluorescence, fluorescence quantum yields, and two-photon properties have been investigated. The two-photon absorption (2PA) cross sections measured by the open aperture Z-scan technique were determined to be 447, 854, 1023, 603, and 766 GM for T1, T2, T3, T4, and T5, respectively. This result indicates that their 2PA cross section values (σ) increase with increasing electron-donating strength of the end group, extending the conjugation length of the system, and introducing electron-withdrawing perfluoroalkyl as side groups to the end donor. In addition, the σ value of T5 is also larger than that of T1, which provides evidence that the σ value is relative to the direction of charge transfer (from the ends to the center of the molecule or from the center to the ends). Moreover, significant enhancement of the two-photon absorption cross section was achieved by introducing a thiophene moiety to a conjugated C==C bond. At the same time, the optical limiting behavior for these chromophores was studied by using a focused 800 nm laser beam with pulses of 140 fs duration. It was found that these molecules also exhibit good optical limiting properties. These initial results clearly demonstrate that multi-branched triazine chromophores are a highly suitable class of two-photon absorbing materials.