Using first-principles quantum mechanical calculations, we investigate the electric field amplification in hybrid nanostructures composed of few-atom Ni linear chains attached to an organic molecule. We found that the pristine Ni linear chains exhibit localized plasmons and produce nanoscale hotspot regions, acting as a plasmon-like nanoantenna. We demonstrate that localized plasmons provide massive electric field amplification in the vicinity of the molecule. Besides, we also investigated the active modulation of the optical absorption spectra due to the inclusion of a positive and/or negative electric field in the Hamiltonian. We believe that the results presented in this work are important for the emerging field of cavity induced photo-catalysis and will aid in the realization of new quantum nano-optic devices. K E Y W O R D S plasmon-molecule hybrids, polaritons, TD-DFT | INTRODUCTIONComplex nanostructures that combine the dissimilar/complementary properties of its components provide a unique platform for the design and the implementation of novel devices. In this context, polaritonic nanostructures combining resonantly matched localized surface plasmons (LSPs: collective coherent oscillation of conduction electrons driven by electromagnetic fields) and molecular excitons (electron-hole pairs created by the absorption of photons) offer unprecedented opportunities in controlling light on the nanoscale. [1][2][3][4][5][6][7][8][9][10] Understanding the nature and tunability of polaritonic states are important and triggered the development of new applications including chemical sensors, [11] pH meters, [12] and solar cell, [13] to list a few. It is well-known that LSPs can confine the electromagnetic energy to nanometric volumes, below the diffraction limits, which can produce a local enhancement of the external electromagnetic field nearby the nanosystem. When this happens, the system acts as a plasmonic nanoantenna able to amplify local electric fields at the nanoscale. [14][15][16][17][18][19][20][21][22][23][24][25][26] On the other hand, the molecular emitters and/or quantum dots can also be utilized to modify the plasmonic response of a metal nanostructure through a local modification of the dielectric environment. Previous studies [4] have shown that the highly enhanced electric field can mediate plasmon-exciton coupling near the surfaces of plasmonic nanostructures, known as hotspots. The strong and localized field in a plasmonic hot spot enhances the interaction between LSPRs and the excitons, much as it enhances other molecular excitations.The light scattering/absorption properties of metal nanoparticles with specific size, geometry, and composition have been accurately calculated within a classical electrodynamics framework based on Maxwell's equations. [27][28][29][30][31][32] Despite the successful use of this technique to model the optical properties of a vast number of pristine and hybrid metal nano-objects, it is purely classical, and consequently it cannot describe accurately the plexcitonic sta...

The third-order nonlinear optical properties of three hydrazone derivatives, namely, ethyl 2-((2E)-2-(4-(dimethylamino)benzylidene]hydrazinyl)-5-nitrobenzoate, ethyl 2-((2E)-2-(4-chlorobenzylidene)hydrazino)-5-nitrobenzoate, and methyl 5-nitro-2-((2E)-2-(4-nitrobenzylidene)hydrazino)benzoate were investigated by the single beam Z-scan technique with nanosecond laser pulses at 532 nm. The compounds were doped into PMMA (poly (methyl methacrylate)), and their third-order nonlinearity was studied with a prospective of reaching a compromise between processability and high nonlinear optical behavior. The optical limiting study of the samples was carried out at 532 nm. The measured values of the third-order nonlinear susceptibility, χ(3), and the nonlinear refractive index, n 2 , are of the order of 10 − 13   esu and 10 − 11   esu , respectively. The nonlinear absorption in materials was attributed to reverse saturable absorption. The results are quite promising for possible applications in photonic devices.