Acyclic donor–acceptor–donor chromophores for large enhancement of two-photon absorption cross-section in the presence of Mg(II), Ca(II) or Zn(II) ions

Two new chromophores in the format, donor–acceptor–donor, have been synthesized in high yields from easily available starting materials. These compounds do not show any two-photon absorption (TPA) cross-section in the wavelength range, 780–900 nm when probed by the Z-scan technique with a femtosecond laser. However, in presence of Zn(II), Ca(II) or Mg(II) ion, each compound gives exceptionally large TPA cross-section in the same wavelength range.