Absorption Spectroscopy Study Of Several Typical Dyes In Solvents Under High Pressure

The dye brings people a more colorful life, it is widely used in fabric dyeing andprinting. As the representative of the typical dyes, methylene blue (MB), acridineorange (AO), and eosin Y (EY) have unique optical properties about chemical andphysical. Under ambient condition, there are two kinds of dye molecules in thesolution, which are monomer and dimer respectively, in a state of monomer–dimerdynamic equilibrium. The absorption spectra properties of these two kinds moleculesare different. We studied the absorption spectra of dye solution under high pressure,and achieved a series of new results with important significance.We took the absorption spectra measurement about MB and AO solution underhigh pressure respectively. The solvents we conducted in the MB experiment werewater and the4:1methanol-ethanol solvent. The absorptance ratio of monomer anddimer was decreased with the increasing pressure, which mean that high pressure canlead to dimer formation. On release of pressure, the changes of the absorption spectraunder high pressure were reversible and the absorptance ratio return to the initialvalue. Pressure effects on the AO experiment are similar.In order to take a further study about the effects of pressure on different type ofdyes, we measured the absorption spectrum about EY under high pressure. EYabsorption spectra were different in different solvents, which was caused by thesolvent effect. Pressure effect on EY molecular aggregation behavior was differentfrom the MB and AO. For EY molecular structure is different from MB’s and AO’s.The carboxyl substituent plays an important role, it forms hydrogen bonds withsolvent molecules, weaks the force between the dye monomer, thereby reduces theeffect of pressure on dimer formation. We found that the higher the polarity of solvent, the lower redshift degree of EYmonomer absorption peak position with the increaseing pressure. The combinationeffects of pressure and polar solvent lead to this result. High pressure effect decreasedthe molecular absorption level, while the orientation force between solvent moleculesand the dye monomer molecule increased the excited state energy of the dyemonomer molecule. The combination of these two kinds of function redshift degree ofEY monomer absorption peak position was lower in solvent with higher polarity.Our research are great significance for studying the chemical reaction andmolecular level change of dye molecules under high pressure.