Competition among steric vs resonance forces and conformational switchover: possible pseudo-Jahn-Teller effects and saturation of hyperpolarizabilities in Brooker’s zwitterions
- 1Department of Chemical Sciences, University of Johannesburg, Auckland Park, PO Box 524, Johannesburg, 2006 South Africa
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.
Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s00894-026-07040-8.
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BibTeX
@article{pant2026competition,
title = {{Competition among steric vs resonance forces and conformational switchover: possible pseudo-Jahn-Teller effects and saturation of hyperpolarizabilities in Brooker’s zwitterions}},
author = {Divya Pant and Bharati Bamana and Sanyasi Sitha},
journal = {Journal of Molecular Modeling},
year = {2026},
month = nov,
doi = {10.1007/s00894-026-07040-8},
url = {https://doi.org/10.1007/s00894-026-07040-8},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Competition among steric vs resonance forces and conformational switchover: possible pseudo-Jahn-Teller effects and saturation of hyperpolarizabilities in Brooker’s zwitterions
AU - Divya Pant
AU - Bharati Bamana
AU - Sanyasi Sitha
PY - 2026
DA - 2026/11/03
JO - Journal of Molecular Modeling
DO - 10.1007/s00894-026-07040-8
UR - https://doi.org/10.1007/s00894-026-07040-8
AB - 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. Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s00894-026-07040-8.
SN - 1610-2940
SN - 0948-5023
ER -