The work presented in this thesis comprises the synthesis and examination of several series of azo dyes of general structure (I) where Y incorporates the terminal nitrogen atom in a five- or six-membered saturated heterocyclic ring system, and Ar is an aromatic carbocyclic or heterocyclic residue, often containing substituent groups. Results are\ud interpreted in terms of the effect of Ar and Y. (electronic and steric) on the conjugation of the lone pair of electrons of the terminal nitrogen atom with the rest of the system. Thus, -the pyrrolidinoazo dyes (Y=-CH2CH2-)\ud absorb at similar wavelengths to their NN-diethyl analogues whilst the corresponding piperidino dyes (Y=-CH2CH2CH2-) show hypsochromic shifts of ^max The presence, of a Y-heteroatom in a six-membered saturated ring increases this hypsochromic effect.\ud \ud \ud Absorption bands of the mono-protonated chromogens have also been examined; in the azobenzene series it is found that variation of the terminal amino group produces a change from almost exclusive protonation at the ß-azo nitrogen atom (azonium'ion) to nearly quantitative protonation at the terminal nitrogen atom (ammonium ion).\ud \ud \ud Trends in the p. m. r. spectra'of the dyes have been noted. Fastness properties of the dyes'on polyester are given. Light fastness ratings are generally low, although the presence of a Y-heteroatom in the six-membered terminal amino ring is advantageous, resulting in values approaching those of the NN-diethyl counterparts. The light fastness\ud properties of monoazo dyes are discussed generally
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