First principle investigations of long‐range magnetic exchange interactions via polyacene couplers

The electronic and magnetic properties of polyacenes become quite fascinating as the number of linearly conjugated benzene rings increases. Higher‐order conjugated polyacenes develop radicaloid characters due to the transition of electronic structures from closed‐shell to the open‐shell system. Here...

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Bibliographic Details
Published in:International journal of quantum chemistry 2021-10, Vol.121 (20), p.n/a
Main Authors: Kaur, Prabhleen, Ali, Md. Ehesan
Format: Article
Language:English
Subjects:
Benzene
Chemistry
Couplers
Density functional theory
DFT
Energy gap
Exchanging
First principles
Hydrocarbons
intramolecular exchange interactions
long‐range interactions
Magnetic properties
Molecular orbitals
organic diradicals
Physical chemistry
polyacene
Quantum physics
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Summary:The electronic and magnetic properties of polyacenes become quite fascinating as the number of linearly conjugated benzene rings increases. Higher‐order conjugated polyacenes develop radicaloid characters due to the transition of electronic structures from closed‐shell to the open‐shell system. Here we have investigated the role of such polyacenes as the magnetic coupler when placed between the two spin‐sources based on nitroxy radicals. To do so, the magnetic exchange interactions (2J) are computed employing broken‐symmetry (BS) approach within the density functional theory (DFT). In this approach, various genre of exchange‐ correlation (XC) functionals such as generalized gradient approximation (GGA), meta‐GGA, hybrid functional, constrained spin density (i.e. CDFT) and on‐site Coulomb correlation corrected GGA + U functionals are adopted. All DFT based calculations estimate an exponential increase in 2J values with the length of the couplers. This observation has been understood in terms of increase in number of near‐degenerate or quasi‐degenerate molecular orbitals (MOs), reduction of HOMO‐LUMO energy gap and descend of low‐lying excited states as the number of fused benzene rings are increased. Generally, the magnetic exchange interactions decrease rapidly with the distance between the two localized spin centers. However, the highly conjugated polyacenes couplers, unexpectedly, show a remarkably reverse trend. In this work, we have performed an in‐depth investigation based on the variety of density functional theory (DFT) based methodologies to unravel the origin of this reverse trend along with long‐range exchange interactions.
ISSN:0020-7608
1097-461X
DOI:10.1002/qua.26756