We report on the design, synthesis and optical properties of new two-photon absorbing multi-branched chromophores, based on a pyridine core. Measurements of TPA using the two-photon fluorescence method in the fs regime indicate that these chromophores exhibit two-photon absorption. We show that a change of the substitution of the electron-acceptor core influences significantly the TPA cross sections. Moreover, upon protonation, the TPA properties are greatly enhanced in the 700-900 nm range. Thus, these molecules can be used as pH-sensitive TPA dyes. Preliminary results related to biological applications will be presented as well.