A comparative study on the aggregate formation of two oxazine dyes in aqueous and aqueous urea solutions

Spectroscopic investigation of interaction of Nile Blue A, a potent photosensitizer, with bile salts in aqueous medium

“…S1 in Supplementary Material). Moreover, the spectral profile of NB in presence of premicellar concentrations of NaDC is very similar to the spectrum of NB at high concentration (>3 Â 10 À5 M) in aqueous medium, where NB is known to form dimers [33]. Thus the new absorption band in the present study can be attributed to the NB dimers in presence of premicellar concentrations of NaDC.…”

“…The H-dimers show a hypsochromic shift whereas the J-dimers show bathochromic shift in their absorption maximum as compared to the monomeric absorption. In aqueous medium, NB is known to form both H-dimer ( v ¼ 16978 cm À1 ; 598 nm) and J-dimer ( v ¼ 15480 cm À1 ; 646 nm) above concentration of 3 Â 10 À5 M [33]. Thus the absorption at 598 nm and 650 nm, in the present study, can be rationalized by considering the formation of both H-and J-dimers in presence of premicellar concentrations of NaDC.…”

“…NB is known to exist almost in its monomeric form at concentrations below 3 Â 10 À5 M in aqueous medium [33]. Since the concentration of NB in the present study is maintained at 5 Â 10 À6 M, NB is expected to be completely in its monomeric form.…”

Spectroscopic characterization and aggregation of azine compounds in different media

“…In Figure 4, the curves a-d can be attributed to the monomer of dye (yellow solutions), curves e-f as a mixture of monomer and aggregate (orange solutions) and curves g-l as a mixture of monomer and aggregate where the aggregate predominated (red solutions). Over the concentration range studied, the Lambert-Beer Law was not obeyed and the appearance of a new band was rationalized in terms of dye aggregation [10,28].…”

“…In such cases the molecular nature of the dyes is strongly affected by ionic strength, temperature, presence of organic solvents, dye concentration and structure. Aggregation may rise with an increase of dye concentration or ionic strength, but will decrease with rising temperature or the addition of organic solvents [9,10].…”