Enhanced optoelectronic properties with aromatic bridges: A computational study on N‐methyl pyridinium and phenolate types of push‐pull zwitterions

Abstract

A series of zwitterions with varying bridges, connecting N‐methyl pyridinium acceptor, with phenolate donor, are investigated using various methodologies like, HF, B3LYP, CAM‐B3LYP and ωB97xD. In this systematic study effects of various mono aromatic rings as bridges, on the response properties like, the dipole moments (μ), polarizabilities (α), hyperpolarizabilities (β) and adiabatic absorptions were analyzed using CPHF and TDDFT (or TDHF) theories. Compared to many traditional bridges, as well as without a bridge, enhanced nonlinear optical (2ND order NLO) responses were observed for these aromatically bridged zwitterions (with benzene ring as bridge ~5.3 times and ~7.9 times enhanced hyperpolarizabilities were observed compared to either the ethylene bridge or without any bridge cases, respectively). Also, many significant differences and large enhancements in response properties were observed compared to our earlier works on non‐zwitterionic system (~4.3 times enhanced hyperpolarizability—benzene as bridge case). For some bridge cases, 10‐ to 15‐fold enhanced hyperpolarizabilities were observed compared to without any bridge case. This work reports a class of non‐TICT chromophores, promoting bridge aromaticity control on structure–property correlation, as a suitable and efficient chromophore design strategy to create a wide range of function molecular chromophores. Also, unidirectional natures of response properties and large dipole moments can make these zwitterions suitable 1D‐molecular materials for various contemporary technological applications, as poled polymer‐based materials.