The synthetic route of the dyes is shown in Scheme 1. Intermediate 1 was prepared from arylamine via alkylation reaction
with dibromoalkane or 1-bromoalkane in the presence of KOH in
DMSO, respectively. The intermediates1were then converted to
the corresponding dialdehydes 2by VilsmeiereHaack reaction in
the presence of DMF and POCl3. Finally, the dialdehydes 2were
condensed with cyanoacetic acid to give the target dyes (SDD1e4
andRD)by the Knoevenagel condensation reaction in the presence
of piperidine. All the intermediates and target dyes were confirmed
by standard spectroscopic methods