In this study, we present a scheme for the evaluation of electron delocalization and conjugation efficiency in lineraly pi-conjugated systems. The scheme, based on the natural bond orbital theory, allows monitoring the evolution of electron delocalization along an extended conjugation path as well as its response to chemical modification. The scheme presented is evaluated and illustrated by means of a computational investigation of;pi-conjugation in all-trans polyacetylene [PA; H(-CH=CH)(n)-H], polydiacetylene [PDA, H(-C C-CH CH)(n)-H], and polytriacetylene [PTA, H(-C C-CH=CH-C C)(n)-H] with up to 180 carbon atoms, all related by the number of ethynyl units incorporated in the chain. We are able to show that for short oligomers the incorporation of ethynyl spacers into the PA chain increases the pi-delocalization energy, but, on the other hand, reduces the efficiency with which pi-electron delocalization is promoted along the backbone. This explains the generally shorter effective conjugation lengths observed for the properties of the polyeneynes (PDA and PTA) relative to the polyenes (PA). It will also be shown that the reduced conjugation efficiency, within the NBO-based model presented in this work, can be related to the orbital interaction pattern along the pi-conjugated chain. We will show that the orbital interaction energy pattern is characteristic for the type and the length of the backbone and may therefore serve as a descriptor for linearly pi-conjugated chains.
Bruschi, M., Limacher, P., Hutter, J., Luethi, H. (2009). A Scheme for the Evaluation of Electron Delocalization and Conjugation Efficiency in Linearly pi-Conjugated Systems. JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 5(3), 506-514 [10.1021/ct8004358].
A Scheme for the Evaluation of Electron Delocalization and Conjugation Efficiency in Linearly pi-Conjugated Systems
BRUSCHI, MAURIZIO;
2009
Abstract
In this study, we present a scheme for the evaluation of electron delocalization and conjugation efficiency in lineraly pi-conjugated systems. The scheme, based on the natural bond orbital theory, allows monitoring the evolution of electron delocalization along an extended conjugation path as well as its response to chemical modification. The scheme presented is evaluated and illustrated by means of a computational investigation of;pi-conjugation in all-trans polyacetylene [PA; H(-CH=CH)(n)-H], polydiacetylene [PDA, H(-C C-CH CH)(n)-H], and polytriacetylene [PTA, H(-C C-CH=CH-C C)(n)-H] with up to 180 carbon atoms, all related by the number of ethynyl units incorporated in the chain. We are able to show that for short oligomers the incorporation of ethynyl spacers into the PA chain increases the pi-delocalization energy, but, on the other hand, reduces the efficiency with which pi-electron delocalization is promoted along the backbone. This explains the generally shorter effective conjugation lengths observed for the properties of the polyeneynes (PDA and PTA) relative to the polyenes (PA). It will also be shown that the reduced conjugation efficiency, within the NBO-based model presented in this work, can be related to the orbital interaction pattern along the pi-conjugated chain. We will show that the orbital interaction energy pattern is characteristic for the type and the length of the backbone and may therefore serve as a descriptor for linearly pi-conjugated chains.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.