Plasmon-Induced Nonlinear Optical Response of <i>N</i>,<i>N</i>′-Dioctyl-3,4,9,10-perylenedicarboximide Nanoribbons Doped with Gold Nanoparticles: Implications for Optical Limiting Applications

Tailoring the inherent optical responses of π-conjugated organic semiconducting materials by integrating them with plasmonic entities has garnered substantial research attention. Herein, we demonstrated a superior optical nonlinearity of nanoribbons of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) integrated with Au nanoparticles (NPs) using an open aperture Z-scan measurement with a Q-switched Nd:YAG laser of wavelength 532 nm and pulse width 7 ns. These integrated one-dimensional nanohybrid systems exhibited an effective nonlinear absorption (NLA) coefficient, βeff of 74 cm/GW at an on-axis input intensity, I0 = 0.27 GW/cm2, which is 3.08 and 1.35 times higher than those of the bulk PTCDI-C8 (monomers) and their pristine nanoribbons, respectively. The enhanced nonlinear optical activity was attributed to the exhibition of strong reverse saturable absorption (RSA) that results from the synergistic effects of inherent plasmonic oscillations of Au NPs (470–580 nm) and the characteristic excitonic transition of PTCDI-C8 nanoribbons (506–536 nm). Theoretical studies carried out using the finite-difference time-domain (FDTD) simulations on different models of Au-PTCDI-C8 nanohybrids revealed the strong coupling of an induced plasmonic hotspot around the Au NPs with PTCDI-C8 nanoribbons. Around 60 times enhancement in E-field intensity in the vicinity of Au NPs was theoretically monitored on integrated PTCDI-C8 nanoribbons, which is believed to be responsible for their enhanced nonlinear optical responses. Furthermore, these nanohybrids exhibited a limiting threshold of 1.75 J/cm2, comparable to or better than that of recently reported π-conjugated and nanohybrid materials, highlighting the efficacy of this approach in developing optical nanomaterials with exceptional nonlinear absorption characteristics.