Novel highly conjugated push–pull 4,5-diazafluoren-9-ylidene based efficient NLO chromophores as a springboard for coordination complexes with large second-order NLO properties

Two new ligands L n: N,N-dibutyl-(4,5-diazafluorenyl-9-ylidene- penta-1,3-dienyl)-amine (L 2) and 9-[(1-azulenyl)methylene]-4,5- diazafluorene (L 3), along with the related Zn(ii) complexes with ancillary ligands of different electron withdrawing strengths ([Zn(CH 3CO 2) 2L n], [Zn(CF 3CO 2) 2L n] and [Zn(CF 3SO 3) 2L n]) were prepared and characterized. Their remarkable second-order NLO properties were investigated using the EFISH technique. The μβ 1.91 value of [Zn(CF 3SO 3) 2L 2] is strongly dependent on concentration, reaching, to our knowledge, the highest value reported for a Zn(ii) complex.