Potential Third-Order Nonlinear Optical Response Facilitated by Intramolecular Charge Transfer in a Simple Schiff Base Molecule: Experimental and Theoretical Exploration

A Schiff base, namely,
4-[(2-hydroxy-3-methoxybenzylidene) amino]
benzoic acid (L1), has been synthesized by the condensation
reaction. It has been characterized by Fourier transform infrared
spectroscopy , UV–vis spectroscopy, single-crystal X-ray diffraction,
and DFT/B3LYP calculations. Single-crystal X-ray crystallographic
analysis revealed that L1 exists in the zwitterionic
(N–H···...O) form. The supramolecular interactions
were investigated by Hirshfeld surface analysis. In addition, third-order
nonlinear optical (NLO) properties of L1 were also investigated.
The nonlinear refractive index (n2), nonlinear absorption
coefficient (β), and the third-order NLO susceptibility (χ(3)) have been estimated at different concentrations and at
different laser powers using close and openaperture Z-scan data. The
values of the parameters were found to be varying almost linearly
with concentration and power. The present study revealed the utility
of the material for various optoelectronic devices such as optical
switches, optical data storage devices, and optical sensors. The optical
limiting study reveals that this material can also be exploited as
an instrument protector from unwanted laser illumination. Furthermore,
the NLO behavior of L1 has also been studied by B3LYP/6-311++G­(d,p)
results.