Synthesis and Z-scan measurements of third-order optical nonlinearity in push–pull molecules with dihydroxylethyl amino donor and nitro acceptor

Novel azo diol chromophores were synthesized through multi-step azo-coupling reaction and characterized by NMR, IR, and UV. The third-order NLO properties of the chromophores were investigated. The measurements of second hyperpolarizabilities were performed using single-beam Z-scan technique with picosecond laser pulses at 1064 nm in DMF solutions. Our results indicate that larger second hyperpolarizabilities γ can be readily obtained in such chromophores because of increase of molecular conjugation length and donor–acceptor conjugation path. Further enhancement of γ has been achieved via replacement of phenyl rings in the conjugated backbone by heteroaromatic spacers such as benzothiazole and pyrimidine rings. Therefore, it is very probable that the increase in the obtained γ values considerably arises from the conjugation path of the delocalized electrons for large third-order nonlinear optical effects.