General trends in the development of investigations of isosbestic point, involving the chemical reaction in aqueous solutions are considered. The electronic absorption spectra, fluoresce spectral, equilibrium, and terminological aspects, as well as the possible schemes of formation of two compounds at the same wavelength, are discussed. The contributions of different methods to estimate the concentration of a substance by isosbestic point are analyzed. The interrelationship between the characteristics isosbestic point and phase rule is discussed.

The association behavior between Acid-Base indicators in aqueous solution has been studied by UV–vis spectroscopy. The spectroscopic results show that association are formed evidenced by slightly red shift to lmax = 470nm and large hypo-chromic shift  in absorbance signal upon addition of azo dye  with creating new bands.  Present of broad bands and isobestic point that indicate formation of simple dyes aggregate monomer- dimmer equilibria in neutral media. The degree of association depends on the concentration of methyl orange, Co-solvents, and   ionic strength of the medium.

The electronic absorption spectra of some azo dyes in various solvents of different polarities have been studied at room temperature. The solvent effects on the wave numbers of the absorption band maxima (vmax) were discussed using the following solvent parameters, refractive index, n, dielectric constant, ε, empirical Kamlet–Taft, Catalân and Hansen solvent parameters. The solute–solvent interactions were determined based on multilinear solvation energy relationships concept. The fitting coefficients obtained from this analysis allowed us to estimate the contribution of each type of interactions to the total spectral shifts in solution. The established dependences between (vmax) and the solvent parameters emphasize that the visible band of the studied molecules is affected by both non-specific and specific solute–solvent interactions.

تمت دراسة سلوك الارتباط بين مؤشرات القاعدة الحمضية في المحلول المائي المخزن (pH = 4) بواسطة تقنية التحليل الطيفي UV-Vis في درجة حرارة الغرفة. أظهرت نتائج التحليل الطيفي أن الارتباط يتشكل من خلال تحول أحمر شديد إلى max = 485 نانومتر وتغير كبير للكروم في إشارة الامتصاص عند إضافة صبغة سابقة. تمت مناقشة أطياف الامتصاص الإلكتروني المتمثلة في نطاقات التوسيع وعدم وجود نقطة متساوية التي تشير إلى تكوين مجاميع صبغية أعلى مرتبة من النوع J-الكلي كنتيجة كتغير في الأس الهيدروجيني للوسط تمت مناقشته وفقًا لنظرية exciton kasha.