Synthesis and Characterization of Novel Carbazole Based Dyes

Abstract

In this work, 9H-carbazole acted as precursor to synthesize a new organic dye, which involved the alkylation of carbazole with butyl bromide in the presence of phase transfer catalyst tetrabutylammonium bromide (TBAB) to give BC (9-butyl-9H-carbazole) followed by the formylation with hexamethylenetetramine (HMTA) in the presence of trifluoroacetic acid (TFA) and tetrahydrofuran (THF). Formyl groups at 3- and 3,6-positions afforded CC (9-butyl-9H-carbazole-3-carbaldehyde) and CD (9-butyl-9H-carbazole-3,6-dicarbaldehye), respectively. The formylation reaction with HMTA suffered with low yield, therefore another methodology was adopted for the formylation of BC with POCl₃ in the presence of dry DMF to afford CC and CD. Then condensation reaction was carried out CC and CD with cyanoacetic acid in the presence of ammonium acetate as catalyst. This reaction resulted in formation of CA (3-(9-butyl-9H-carbazol-3-yl)-2-cyanoacrylic acid) and DA (3,6-(9-butyl-9H-carbazol-3-yl)-2,2'-cyanoacrylic acid. All the synthesized compounds were characterized by FTIR, GC-MS, MS and UV-visible methods. The UV-Visible absorption spectra of CA was observed at 239 nm while the absorption region is from 190 nm to 340 nm and DA shows the absorption peak at 320 nm while the absorption region is from 290 to 440 nm. The energy band gaps for CA and DA were found to be 5.2 eV and 3.6 eV, respectively.