Synthesis and spectroscopic properties of symmetrically substituted two-photon absorbing molecules with rigid elongated π-conjugation

A series of symmetrical molecules with substituted acetylene as central rigid elongated conjugation have been designed and synthesized. These molecules consist of a typical D-π-D structure, where N,N-dihexylamino and substituted acetylene are employed as donor (D) and π-conjugated center (π), respectively. Single and two-photon spectroscopic properties of these molecules were investigated systematically. One derivative with great enhancement on the two-photon absorption cross-section in 820 nm, which is among the best output wavelength range of a typical Ti:Sapphire femtosecond laser, could be obtained by inserting an anthracene ring into the rigid elongated π-conjugation. Such kind of structure modification is expected to be helpful in designing better organic nonlinear optical materials for biological imaging.