Unraveling the Push-Pull Effect in Acenes, Polyenes and Polyynes

Area of Science:

• Computational chemistry
• Organic chemistry
• Quantum chemistry

Background:

• Substituent effects (SEs) are crucial for predicting molecular reactivity.
• Polyene, polyyne, and acene derivatives serve as precursors for diverse applications.
• Understanding electronic interactions in these systems is key to designing new materials.

Purpose of the Study:

• To quantitatively describe the electron-donating and withdrawing properties of spacers in Y-R-X systems.
• To investigate the dependence of substituent electronic properties on spacer type, length, and the Y group.
• To compare the cSAR and SE stabilization energy (SESE) approaches for describing SE weakening with increasing spacer length.

Main Methods:

• Computational modeling of Y-R-X systems with varying Y, X, and R (polyene, polyyne, acene).
• Application of the charge of the substituent active region (cSAR) approach to quantify spacer properties.
• Utilizing electron density of delocalized bonds (EDDB) and EDDB differential maps to analyze electron delocalization and substituent effects.

Main Results:

• Established quantitative relations for spacer electron-donating/withdrawing properties based on spacer type and length (n).
• Demonstrated that substituent electronic properties are influenced by the spacer and Y group, illustrating reverse SE.
• Showcased how EDDB differential maps effectively visualize the impact of X substitution on electron delocalization.

Conclusions:

• The cSAR approach provides a robust method for characterizing electronic properties in conjugated systems.
• Spacer length and type significantly modulate substituent effects, offering a tunable platform for electronic property control.
• Charge transfer via resonance plays a key role in the observed electronic interactions within these molecular systems.