Effect of Molecular Structure on the B3LYP-Computed HOMO-LUMO Gap: A Structure -Property Relationship Using Atomic...

Area of Science:

• Computational Chemistry
• Materials Science
• Organic Chemistry

Background:

• Compounds with small highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps (E_gap) exhibit desirable reactivity for various applications.
• Identifying such compounds is challenging and costly due to the vast number of potential molecular structures.

Purpose of the Study:

• To develop a quantitative structure-property relationship (QSPR) model for predicting the E_gap of organic compounds.
• To utilize atomic Signatures as molecular descriptors to establish structure-property correlations.
• To create an efficient screening tool for identifying molecules with low E_gap.

Main Methods:

• Employed atomic Signatures as molecular descriptors.
• Utilized B3LYP computation for E_gap values.
• Constructed a QSPR model using forward-stepping multilinear regression and leave-one-out cross-validation.
• Validated the model with an external test set.

Main Results:

• Achieved a high regression coefficient (r^2) of 0.86 and predictability (q^2) of 0.76.
• Identified atomic fragments with π-bonds in aromatic systems as key descriptors, explaining approximately 50% of the variance in E_gap.
• Demonstrated that these fragments decrease E_gap due to π-electron delocalization and enhanced reactivity.

Conclusions:

• Atomic Signatures provide a robust method for correlating molecular structure with E_gap.
• The developed QSPR model serves as a reliable and cost-effective initial screening tool for discovering compounds with low E_gap.
• The findings facilitate the targeted design of reactive organic molecules.