Nonlinear optical properties of crocin: From bulk solvent to nano-confined droplet

Crocin has a strong Two-photon Absorption (TPA) capability that makes it suitable for medicine and photonic devices. To study the linear and nonlinear optical properties of crocin in solvent and Microemulsion (MEs), Z-scan instruments, Uv-Vis, and fluorescence were used. Nonlinear absorption coefficient (beta), nonlinear refractive index (n(2)), third-order susceptibility (chi(R)), and second-order molecular hyperpolarizability (gamma(R)) values were extracted from the Z-scan instrument The beta and n(2) reduce with the increase in solvent's dielectric constant (epsilon). In crocin mixed with MEs, the nonlinear optical values depend on the size and concentration of the droplet at constant crocin concentration. The MEs can enhance the value of beta as compared with other solvents. A red shift in absorption spectra of crocin was observed with an increase in epsilon. However, the absorption peak was constant in the MEs. The ratios of the excited state to the ground state of the dipole moments (mu(e)/mu(g)) of crocin in the solutions were determined by the quantum perturbation theory. It was shown that mu(e)/mu(g) has similar behavior with 1/gamma(R). The value of mu(g) and gamma(R) are reduced with an increase in epsilon. (C) 2018 Elsevier B.V. All rights reserved.