Studies on Azo Compounds: Part V-Spectrophotometric Studies on Some Quinoline Azo Dyes

In continuation of our spectrophotometric studies on azo compounds I -6, the UV, visible and IR spectra of some new azo dyes containing a quinoline nucleus have been studied. The absorption spectra of azobenzene and its derivatives 7 -15 as well as those of azo dyes containing heterocyclic moieties 16 -18 have been studied by some other workers. The studies reveal that the absorption spectrum shows bands due to electronic transitions within the moieties attached to the azo group leading to absorption in the UV region and the bands corresponding to the electronic excitations of the nand n-electrons on the azo group. In the present investigation, two groups of disperse dyes I and II, prepared by the authors earlier2, were used. Melting points, analysis and light fastness of the compounds have been given. The UV and visible spectra of the dyes were taken on Pye Unicam Sp 800 and Sp 8000 spectrophotometers in different solvents purified by the recommended procedures. The IR spectra were obtained as KBr discs using Pye Unicam Sp 200 G and Sp 1000 spectrophotometers. The dyes are listed in Table I. due to a red shift of an essential quinoline band which lies beyond 200 nm. The band has shifted under the effect of the substituent on the quinoline ring. Thus, the band can be assigned to transition to the (IBa<-IJ stateI9.20. The second band at 250 nm is assigned to transition to the eBb <-!J state; it is akin to that observed in the spectra of quinoline in hexane or ethanol21 and of naphthalene derivatives22. It seems that this band is not sensitive to changes in the polarity of the solvent. The last band is broad and splits into two bands located at 335 and 352 nm in the case of ethanol. The band at 335 nm can be attributed to the transition to the ILa state, while that at 352 nm may be assigned to ILb state as well as a CT interaction from the amino group to the quinoline nucleus. The CT nature of the last band can be substantiated by broadet1ing the band and by varying its position on changing the polarity of the solvent. The ILa and ILb bands are also observed in the spectra of quinoline derivatives either overlapping each other or reversed in position 23,24.