Nonlinear Optical Properties and Electronic Structure of Bio-Active Molecules: A Comparative Study Using Laser Z-Scan Technique and Gaussian/Siesta Simulation
Keywords:
Nonlinear Optics (chi^3), Laser Z-Scan Technique, Density Functional Theory (DFT), Bio-Active Molecules, Gaussian/Siesta Simulation, Optical Limiting, Reverse Saturable Absorption (RSA)Abstract
The research has focal points on nonlinear optical (NLO) response of the third-order as well as the electronic structure of two different bio-active heterocycles meso-tetrakis(4-methoxyphenyl) porphyrin (BM-I) and bis(4-hydroxy-3-methoxyphenyl) hepta-1,6-diene-3,5-dione (BM-II). High-sensitivity single-beam Z-scan technique with Q-switched Nd:YAG laser (532 nm, 5 ns) to measure the nonlinear refractive index n2 and nonlinear absorption coefficient beta was a method of characterization. The results of the experiments were verified by the calculations of comparative Density Functional Theory (DFT) implementations with localized Gaussian-type orbitals (Gaussian 16, B3LYP/6-311G++) and periodic numerical atomic orbital (Siesta 4.1, GGA-PBE/DZP). Both of the compounds were highly Reverse Saturable Absorptiory (RSA) and self-focusing refracting . Porphyrin derivative BM-I exhibited better optical limiting threshold (0.45 J/cm2) and overall susceptibility || () than curcuminoid BM-II, due to extensive 18 -pi electron macrocyclic conjugation. An analysis of the Falconeri model showed that a contribution of thermal lensing was profound superimposed on ultrafast electronic Kerr effect. Intramolecular Charge Transfer (ICT) was found to be the main polarization mechanism by computational analysis. More importantly, Intermolecular band-gap renormalization ( depression) was observed in Siesta simulations, and this clarifies the enhancement in the bulk-phase behavior not seen in isolated-molecule Gaussian models. Research determines hybrid Experimental-DFT screening protocol of bio-photonic limiters.
