Tuning Second-Order Nonlinear Optical Response in 2D L-Serine Derivatives: A Computational Investigation

Abstract

The rapidly expanding field of nonlinear optics (NLO) is setting the pace in photonics and optoelectronics, highlighting the pressing need for materials with superior second-order NLO characteristics. Two-dimensional (2D) organic compounds, identified by their unique structural and electronic properties, have been found to be promising candidates for this role. Herein, we report an investigation of L-serine, a chiral zwitterionic amino acid, and five innovative derivatives to evaluate their performance as building blocks for high-performance two-dimensional nonlinear optical (2D NLO) materials. Utilizing density functional theory (DFT) and time-dependent DFT (TD-DFT) with appropriate basis sets, we thoroughly examine how rational functionalization influences the molecular geometry, electronic structure, and, most importantly, the first hyperpolarizability (β) of these compounds. Our findings show that intentional functionalization, especially with strong electron-withdrawing groups like the p-nitrophenyl sulfonate group, shows a dramatic increase in the β values. This is mainly due to the strong intramolecular charge transfer (ICT) and extended π-conjugation. This work lays down a theoretical basis for understanding the structure-property correlations in L-serine derivatives and provides guidelines for future experimental synthesis of high-performance 2D NLO materials. Keywords: L-Serine derivatives, 2D materials, Second-order nonlinear optics, DFT, Hyperpolarizability, SHG, Computational chemistry, Rational design.