Charge transfer interactions of some aza and styryl analogues of cyanine dyes with thymine, cytosine, adenine, thymidine, uridine and adenosine: Structure:-activity relationship studies

Abstract

UV-visible spectrophotometric studies on the interaction of 2-(4-dimethylaminophenyl)azomethine-1- ethylquinolinium iodide (<strong>I</strong>),4-(4-dimethylaminophenyl)azomethine-l-ethylquinolinium iodide (<strong>II</strong>), 2-(4-dimethylaminostyryl)quinolinium-l-ethyl iodide (<strong>III</strong>) 4-(4-dimethylaminostyryl)quinolinium-l-ethyl iodide (<strong>IV</strong>) with thymine (<strong>V</strong>) in aqueous solutions at 30ᵒC demonstrate the formation of weakly bonded charge transfer (CT) complexes. The absorption bands in the visible region of the CT-complexes are located at longer wavelengths than those of the pure reactants. The amount of the induced red shift depends on the thymine concentration and the type of cyanine dye used. The spectra exhibit isosbestic points. The stability constants (<em>K</em><img src="http://www.niscair.res.in/jinfo/equation99.gif" alt="" border="0" />) and the molar absorptivities of the complexes formed have been calculated assuming the formation of 1:1 complexes. The abilities of the dyes (<strong>I-IV</strong>) to form <strong>CT</strong>-complexes with thymine follow the order: I > II > III > IV. The abilities of thymine (<strong>V</strong>), cytosine (<strong>VI</strong>), adenine (<strong>VII</strong>), thymidine (<strong>VIII</strong>), uridine (<strong>IX</strong>) and adenosine (<strong>X</strong>) to form CT-complexes with azacyanine dye (<strong>I</strong>) follow the order: <strong>X</strong> > <strong>VIII</strong> > <strong>VII</strong> > <strong>V</strong> > <strong>VI</strong> > <strong>IX</strong>. The experimental results have been interpreted in terms of the molecular structure of the interacting molecules and the nature of complexes formed.