Work

Competition among steric vs resonance forces and conformational switchover: possible pseudo-Jahn-Teller effects and saturation of hyperpolarizabilities in Brooker’s zwitterions

Year: 2026

Type: article

Abstract: Context This work reports structure, linear, and nonlinear optical properties of pyridinium imidazolate-based Brooker’s types of zwitterions, with benzene ring(s) as repeating bridges (no bridge to 4-benzene rings). Instead of the expected planar conformations, significant conformational switching was observed for the molecules with 3- and 4-benzene rings as bridges. Such conformational flipping showed a saturation limit for the nonlinear optical response with 3-benzene rings as bridges (CAM-B3LYP: β = 3760.4 × 10 −30 esu and | μβ | close to 0.18 million × 10 −48 esu— among the largest values reported in literature till date ). Thus, an early saturation was observed (with 3-benzene rings as bridges) before pseudo-Jahn-Teller distortion (observed with 4-benzene rings as bridges). This report shows how the gyratory nature of the inter-ring junctions plays significant roles in controlling intramolecular interactions and response properties. This work also shows that structural topography plays vital role in efficient chromophore design. This work reports molecules with extremely large dipole moments, polarizabilities, and molecules also with absorptions in the IR regions of the electromagnetic spectrum (maybe useful to solve transparency-tradeoff problem of nonlinear optics). Methods Geometry optimizations and further computations of all the molecules were performed with Gaussian 09 program, with HF, B3LYP, and CAM-B3LYP methodologies combined with 6-31G(d,p) basis set. For all molecules, computations of adiabatic excitations were carried out using TDDFT and TDHF approaches. For the computations of the response properties (like the nonlinear optical responses), CPHF and CPKS approaches were used. Population studies were carried out to visualize molecular orbitals and electrostatic potential maps. NBO computations were carried out to account atom hybridization and orbital interaction energies.

Source: Journal of Molecular Modeling

DOI: 10.1007/s00894-026-07040-8

Authors: Divya Pant, Bharati Bamana, Sanyasi Sitha

Institution: University of Johannesburg

Language: English

Topic: Nonlinear Optical Materials Research

Subfield: Electronic, Optical and Magnetic Materials

Field: Materials Science

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,290

Funder: University of Johannesburg