Synthesis and nonlinear optical response of silver nanoparticles decorated polydiacetylene composite nanovesicles

We have synthesized, characterized and studied the third-order nonlinear optical properties of polydiacetylene (PDA) nanovesicles decorated by silver nanoparticles. The second molecular hyperpolarizability γ(−ω;ω,−ω,ω) of the sample was investigated by the antiresonant ring interferometric nonlinear spectroscopic (ARINS) technique using femtosecond modelocked Ti:sapphire laser in the spectral range of 720-820 nm. The observed dispersion of γ has been explained in the framework of three-essential states model involving the ground state, a one-photon excited state and a two-photon excited state. The energy of two-photon state, transition dipole moments and line width of the transitions have been estimated. Our investigation reveals that the spectral dispersion characteristic of γ for coated PDA nanovesicles is qualitatively similar to that observed for uncoated PDA nanovesicles but bears no resemblance to that observed in silver nanoparticles. The presence of silver nanoparticles increases the γ values of coated nanovesicles slightly as compared to that of uncoated nanovesicles, suggesting a definite but weak coupling between free electrons of metal nanoparticles and π -electrons of polymer in the composite system.