Synthesis, Photoswitching Behavior and Nonlinear Optical Properties of Substituted Tribenzo[a,d,g]coronene

A family of tribenzocoronene derivatives bearing various substituents (3) were constructed through the Diels-Alder reaction, followed by the Scholl oxidation, where the molecular structure of 3b was determined via single crystal X-ray diffraction analysis. The effect of substitution on the optical and electrochemical property was systematically investigated, with the assistance of theoretical calculations. Moreover, the thin films of the resulting molecules 3b and 3e complexed with fullerene produced strong photocurrent response upon irradiation of white light. In addition, 3b and 3e exhibit a positive nonlinear optical response resulting from the two-photon absorption and excited state absorption processes.

Effects of Different Parts of the Okra Plant (Abelmoschus esculentus) on the Phytosynthesis of Silver Nanoparticles: Evaluation of Synthesis Conditions, Nonlinear Optical and Antibacterial Properties

In this work, stable and spherical silver nanoparticles (AgNPs) were synthesized in situ from silver salt (silver nitrate) using the aqueous extract of the okra plant (Abelmoschus esculentus) at room temperature and ambient pH conditions. The influences of different parts of the plant (such as the leaves, stems, and pods) on the chemical-reducing effectiveness of silver nitrate to silver nanoparticles were investigated. The aqueous extract of the leaves was found to be more effective in the chemical reduction of silver nanoparticles and in stabilizing them at the same time. The silver nanoparticles produced were stable and did not precipitate even after storage for 1 month. The extract of the stem was less effective in the reduction capacity followed by the extract of the pods. The results indicate that the different amounts of phytochemicals present in the leaves, stems, and pods of the okra plant are responsible for the chemical reduction and stabilizing effect. The silver nanoparticles were characterized by UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The surface plasmon resonance (SPR) peak at 460 nm confirmed the formation of silver nanoparticles. The nanoparticles were spherical with an average size of 16 nm and polycrystalline with face-centered cubic (fcc) structures. The z-scan technique was used to study the nonlinear refraction and absorption coefficients of AgNPs at wavelengths of 488 and 514 nm under C.W. mode excitation. The nonlinear refraction index and nonlinear absorption coefficients were calculated in the theoretical equations in the experimental data. The antibacterial properties of the nanoparticles were evaluated against Gram-positive and Gram-negative bacteria.

Pseudospectral implementations of long-range corrected density functional theory

We have implemented pseudospectral density-functional theory (DFT) with long-range corrected DFT functionals (PS-LRC) in quantum mechanics package Jaguar, and applied it in the calculations of geometry optimizations, dimmer interaction energies, polarizabilities and first-order hyperpolarizabilities, harmonic vibrational frequencies, S₁ and T₁ excitation energies, singlet-triplet gaps, charge transfer numbers, oscillator strengths, reaction barrier heights, electron-transfer couplings, and charge-transfer excitation energies. From our accuracy benchmark analysis, PS grids, PS dealiasing functions, PS atomic corrections, PS multigrid strategy, PS length scales, and PS cutoff scheme perform well in PS DFT with LRC density functionals with very small and ignorable deviations when compared to the conventional spectral (CS) method. The timing benchmark study of S₁ excitation energy calculations of fullerenes (C_n , n up to 540) demonstrates that PS-LRC achieves 1.4-8.4-fold speedups in SCF, 22-32-fold speedups in Tamm-Dancoff approximation, and 6-15-fold speedups in total wall clock time with an average error 0.004 eV of excitation energies compared to the CS method.

Remarkable Size Effect on Photophysical and Nonlinear Optical Properties of All-Carboatomic Rings, Cyclo[18]carbon and Its Analogues

Inspired by recent experimental observation of molecular morphology and theoretical predictions of multiple properties of cyclo[18]carbon, we systematically studied the photophysical and nonlinear optical properties of cyclo[2N]carbons (N=3-15) allotropes through density functional theory. This work unveils the unusual optical properties of the sp-hybridized carbon rings with different sizes. The remarkable size dependence of the optical properties of these systems and their underlying nature are profoundly explored, and the relevance between aromaticity and optical properties are highlighted. The extrapolation curves fitted for energy level of frontier molecular orbitals, maximum absorption wavelength, and (hyper)polarizability of considered carbon rings are presented, which can be used to reliably predict corresponding properties for arbitrarily large carbon rings. The findings in this study will facilitate the exploration of potential application of cyclocarbons in the field of optical materials.

Few-Layer Platinum Diselenide as a New Saturable Absorber for Ultrafast Fiber Lasers

A multilayer platinum diselenide (PtSe₂) film was experimentally demonstrated as a new type of saturable absorber with the capability to deliver robust dissipative solitons in a passively mode-locked fiber laser. The PtSe₂ film synthesized by chemical vapor deposition was placed onto the ferule of a single mode optical fiber through a typical dry transfer process. The nonlinear optical measurements reveal efficient saturable absorption characteristics in terms of a large modulation depth (26%) and low saturable intensity (0.346 GW cm^-2) at the wavelength of 1064 nm. An all-fiber ring cavity was built, in which the PtSe₂ film was sandwiched between two ferules as the saturable absorber and Ytterbium-doped fiber was used as the optical gain medium. Robust dissipative soliton pulses with a 3 dB spectral bandwidth of 2.0 nm and a pulse duration of 470 ps centered at 1064.47 nm were successfully observed in the normal dispersion regime. Moreover, our mode-locked lasers also exhibit good long-term stability. Our finding suggests that multilayer PtSe₂ may find potential applications in nonlinear optics and ultrafast photonics.