An insight into the effect of nano-confinement on some of photo-physical parameters of dye

In the current work, at first, water nanodroplets containing Rhodamine B (RhB) were prepared in water-in-oil AOT microemulsions (MEs) at a constant molar ratio of water-to-surfactant (W = 7) species with varying mass fraction of water nanodroplet (MFD). The photo-physical parameters of the dye including the ratio of the excited-to-ground-state dipole moments of RhB and Stokes shift of RhB within water the nanodroplets as well as the apparent refractive index of water nanodroplets and solvent polarity of microemulsions were studied. The quantum mechanical perturbation theory was used for the evaluation of parameters of Stokes shift and the dipole moment of excited-to-ground states of RhB. The Stokes shift of RhB at the 0.002 M decreased with MFD up to 0.04 and then increased with MFD within AOT ME. The dipole moment ratio of the ground-to-excited states (μ_g/μ_e) for RhB at 1.531 × 10^–4 M decreased with MFD, whereas at 0.002 M of the dye, μ_g/μ_e for RhB decreased, as MFD increased up to MFD = 0.04 and then increased with MFD within the AOT MEs. The polarity parameter, for instance, the E_T value of microemulsion system is less than that of the bulk water at a similar concentration. The apparent refractive index of water droplets within water-in-oil AOT microemulsion was different from that of bulk water.