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Updated: Apr 17, 2026

Spatial Separation of Molecular Conformers and Clusters
Published on: January 9, 2014
Quantum chemical study of benzimidazole derivatives to tune the second-order nonlinear optical molecular switching by
Shabbir Muhammad1, Hongliang Xu, Muhammad Ramzan Saeed Ashraf Janjua
1Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun 130024, Pr China.
Abstract:
A novel sequence for reversible second-order nonlinear optical (NLO) molecular switching with protonation/deprotonation has been achieved and tuned as well. The NLO switching with first hyperpolarizabilities (beta(0)) as low as 14 x 10(-30) esu (Off-phase) and as large as 1189 x 10(-30) esu (On-phase) have been computed by using density functional theory (DFT). Remarkably large differences between the beta(0) values of benzimidazole containing chromophores and their deprotonated anions have shown their significant potential for a new type of NLO molecular switching, as (1-(4-methoxyphenyl)-2-(2-thienyl)pyrrolyl)-1,3-benzimidazole anion (1(-)) has a beta(0) value computed to be 61 x 10(-30) esu, which is 4 times larger than its neutral molecule 1. This beta(0) value has been tuned up to 2028 x 10(-30) esu by effective substitutions in the derivatives of 1(-) (1a(-), 1b(-), 1c(-), and 1d(-)). Interestingly, the substituted compounds have illustrated robustly large off-on NLO switching with a difference in beta(0) values of 7, 63, 85 and 75 times larger than their neutral counterparts, respectively. TD-DFT calculations along with natural bond orbital (NBO), frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP) analyses show that the abstraction of an imido proton brings about a change in push-pull configurations resulting in a red shift for both absorption and emission spectra which subsequently leads to a high performance second-order NLO molecular switching. A similar trend of NLO switching in F(-) compounds of these chromophores has also been observed with significantly large beta(0) values having analogous electro-optical properties like deprotonated anions. Furthermore, gas-phase acidity (GPA) calculations for the neutral molecule 1 and its derivatives (1a, 1b, 1c, and 1d) have also revealed that these are rationally potent nitrogen acids and can easily be dissociated to produce stable deprotonated anions.
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