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A Scheme for the Evaluation of Electron Delocalization and Conjugation Efficiency in Linearly π-Conjugated Systems


Bruschi, M; Limacher, P A; Hutter, J; Luethi, H P (2009). A Scheme for the Evaluation of Electron Delocalization and Conjugation Efficiency in Linearly π-Conjugated Systems. Journal of Chemical Theory and Computation, 5(3):506-514.

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(-CC-CH CH)(n)-H], and polytriacetylene [PTA, H(-CC-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.

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(-CC-CH CH)(n)-H], and polytriacetylene [PTA, H(-CC-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.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Date:10 March 2009
Deposited On:31 Jul 2009 08:29
Last Modified:05 Apr 2016 13:13
Publisher:American Chemical Society
ISSN:1549-9618
Publisher DOI:10.1021/ct8004358
Official URL:http://pubs.acs.org/doi/full/10.1021/ct8004358
Permanent URL: http://doi.org/10.5167/uzh-18394

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