Novel pyridinium inner salt dye and its complexes: synthesis, crystal structures and photophysical properties

Two novel metal complexes, namely [Tb2(L)6(H2O)4]·(NO3)6·L2·(H2O)18 (1) and [Hg(L)Cl2]n (2), were obtained by the reaction of D-π-A (D = donor, π = conjugated spacer, A = acceptor) type pyridinium inner salt dye, trans-4-[(p-N,N-dimethylamino)styryl]-N-(2-propanoic-acid) pyridinium (L) with corresponding metal salts. Single crystal X-ray diffraction analyses reveal that compound 1 possesses dinuclear motif in which two Tb(III) ions are linked by four carboxylate groups while complex 2 exhibits 1D chain structure based on Hg(II) ions bridged by carboxylate groups. The linear and non-linear optical properties of complexes 1 and 2 have been studied. Both 1 and 2 exhibit intense single-photon excited fluorescence (SPEF) and two-photon excited fluorescence (TPEF) in the red range. Results show that the replacement of central ions from Hg(2+) to Tb(3+) influence the two-photon absorption cross-section significantly through increasing the density of the chromophore. However, the peak positions of two-photon excited fluorescence are only slightly affected. Compared with L molecule, complex 1 shows enhanced two-photon absorption cross-section and decreased fluorescent lifetime.