Spectroscopic investigations on the H-type aggregation of coumarin 153 dye molecules: role of Au nanoparticles and γ-cyclodextrin.

Here, we study the formation of H-type aggregation of coumarin 153 (C153) dye molecule in presence of Au nanoparticles and the removal of dye aggregation in presence of γ-cyclodextrin (CD) due to confinement of dye molecules inside the nanocavity of γ-cyclodextrin (CD) using steady state and time resolved spectroscopy. Blue shifting of absorption band, photoluminescence (PL) band and the enhancement of decay time of C153 dye confirm the formation of H-aggregation. It is found that the concentrations of γ-CD and Au nanoparticles play an important role on H-type aggregation of dye. The rotational relaxation time of free C153 is 0.113 ns and the average relaxation time of C153 dye are 0.275 ns and 0.425 ns for 2 mM and 5 mM γ-CD confined systems, respectively, indicating the anisotropy increases due to confinement of dye. An associated type anisotropy decay of C153 dye is found at 20 mM concentration of CD may be due to formation of nanotubular aggregates of γ-CD.