A fluorescence approach on the investigation of urea derivatives interaction with a non-PET based acridinedione dye-beta Cyclodextrin (β-CD) complex in water: Hydrogen-bonding interaction or hydrophobic influences or combined effect?

Photophysical studies of resorcinol based acridinedione dyes with beta Cyclodextrin (β-CD) in the presence of urea (U) and tetramethylurea (TMU) were carried out in water. A marked variation in the absorption spectra of dye-β-CD complex was found to be more significant in the case of U rather in TMU. Interestingly, the role of urea on the excited state behavior of dye-β-CD complex is found to be entirely different from that of TMU. The formation of urea-water hydrogen-bonding self assemblies and creation of microspheres of varying environment results in an effective displacement of dye from the hydrophobic nanocavity of β-CD. On the contrary, the dye prefers a more confined hydrophobic micro environment in the presence of TMU. The nature of urea derivative, hydrogen-bonding of urea-water assemblies and hydrophobic influences of methyl moieties in urea molecular framework governs the stability and also the dissociation of dye-β-CD complex. The displacement of dye from the environment of the sugar molecule by urea derivatives is established from fluorescence studies wherein the variation in the spectral behavior of non-PET based dye-β-CD complex is found to be entirely different from that of PET dye. Both hydrogen-bonding along with hydrophobic interactions influences the excited state properties of the both PET and non-PET based acridinedione dyes are elucidated through fluorescence spectral studies. The extent of binding and the microenvironment of the dye in the presence of β-CD and urea are established through molecular docking and fluorescence anisotropy studies.