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Geometry and quadratic nonlinearity of charge transfer complexes in solution: a theoretical study
S Mukhopadhyay1, Ravindra Pandey, Puspendu K Das
1Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India.
The Journal of Chemical Physics
|February 2, 2011
Summary
This study reveals that weak charge transfer complexes formed between methyl-substituted benzenes and acceptors like CHL or DDQ exhibit significant quadratic nonlinear optical (NLO) properties. The parallel displaced geometry is key to these strong NLO responses.
Area of Science:
- Computational Chemistry
- Materials Science
- Nonlinear Optics
Background:
- Weak charge transfer (CT) complexes are formed between electron donors (methyl-substituted benzenes) and acceptors (CHL, DDQ).
- These complexes exhibit unique absorption bands in the visible spectrum due to CT interactions.
- Such interactions are known to induce significant nonlinear optical (NLO) responses.
Purpose of the Study:
- To compute the quadratic nonlinear optical (NLO) properties of weak CT complexes.
- To determine the most probable geometry of these complexes in solution.
- To correlate CT interactions with observed NLO responses.
Main Methods:
- Semiempirical Intermediate Neglect of Differential Overlap (INDO/S) Hamiltonian with single and double configuration interaction (SDCI) for energy level calculations.
- Self-Consistent Reaction Field (SCRF) scheme to incorporate solvent effects.
- Exploration of various relative molecular geometries to find the optimal complex structure.
Main Results:
- Calculated quadratic NLO properties for a class of weak CT complexes.
- Identified the parallel displaced structure as the most probable geometry in solution, with potential twists.
- Established a link between CT interactions, complex geometry, and strong NLO responses.
Conclusions:
- The study elucidates the relationship between molecular structure, charge transfer dynamics, and nonlinear optical properties in weak CT complexes.
- Computational methods accurately predict NLO properties and preferred geometries.
- Findings contribute to the understanding and design of materials with tailored NLO characteristics.
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