Molecular Vibrations Induced Potential Diradical Character in Hexazapentacene

Feng, Yongjun; Zhang, Fengying; Song, Xinyu; Bu, Yuxiang

doi:10.1021/acs.jpcc.6b03891

Cited by 14 publications

(11 citation statements)

References 60 publications

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“…18 They also predicted a transition in electronic structure from discrete molecular orbitals to band picture occurs for octacene onwards. 18 Such interconversion in the electronic structure in polyacenes has consequences on its ground state molecular properties such as optical 19 , magnetic 20 , vibrational, 21 and other spectroscopic properties 22 . Here such linear polyacenes are adopted as the spacers in coupling the conformationally restricted nitroxy-diradicals.…”

Section: Introductionmentioning

confidence: 99%

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Kaur

Ali²

2020

Preprint

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The polyacene tend to transition from closed-shell to open-shell singlet systems with increase in the number of linearly fused benzene rings thus, enriching it's electronic as well as magnetic properties. Here, we have probed the role of such a polyacene couplers in mediating the magnetic exchange coupling between nitroxy radicals. For this, magnetic exchange coupling constants (2J) are computed employing broken-symmetry approach within density functional theory (DFT) as well as symmetry-adopted wave function based multi-configuration approach. Within DFT approach, apart from most commonly used exchange-correlation functional (generalized gradient approximation (GGA), meta-GGA, and hybrid) constrained spin density (CDFT) and on-site Coulomb correlation corrected GGA+U functionals have also been used to evaluate the exchange coupling constants in the diradicals. All DFT based methods approximate an exponential increase in the coupling constant values with increase in the length of the coupler. This is indeed an unexpected observation with no experimental report available to such an outcome by DFT calculations. Therefore, the electronic structures for these diradical systems with the increase in number of benzene rings were looked upon thoroughly. The properties like increase in number of degenerate or quasi-degenerate molecular orbitals (MOs), the lowering in energy of low-lying excited states and the development of intrinsic radical character of the coupler add to the complexity in evaluation of 2J values for such diradical systems with DFT approach. Consequently, wave function based multi-reference approach (CAASCF/NEVPT2) has been adopted. The active space has been limited to π-orbitals which are found to play an important role in the magnetic exchange interactions. With increase in the coupler size, the active space even with only π obitals would increase enormously which could not be taken into account even in the CASSCF study. The limited active space calculations also indicate quite strong exchange interaction, thus in principle, supporting the DFT observations of long-range magnetic exchange interactions but not an exponential increase in 2J with length of couplers.

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Section: Introductionmentioning

confidence: 99%

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Kaur

Ali²

2020

Preprint

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“…Such interconversion in the electronic structure of polyacenes i.e. from closed-shell singlet to open-shell singlet has consequences on its ground state molecular properties such as optical [28], magnetic [27], vibrational, [29] and other spectroscopic properties [30]. Here such linear polyacenes are adopted as the spacers in coupling the conformationally restricted nitroxy-diradicals.…”

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confidence: 99%

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

Kaur¹,

Ali²

2021

Int J of Quantum Chemistry

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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 spinsources 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 quasidegenerate 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. K E Y W O R D SDFT, intramolecular exchange interactions, long-range interactions, organic diradicals, polyacene | INTRODUCTIONMolecular magnets based on the stable organic radicals have attracted enormous attention due to their potential applications in spintronics, [1] magnetic logic devices, [2] and quantum computers. [3] The non-magnetic spacer between the radical centers control the nature and strength of intramolecular magnetic exchange interactions. [4][5][6] The seamless π-conjugations between the radical centers and spacer play a vital role in magnetic couplings. [7][8][9] Strong magnetic exchange interactions are reported mostly for couplers with smaller lengths. [10] However, the fascinating long-range couplers desired [11,12] for magnetic and spintronic applications are relatively less explored. On the top of it accomplishment of long range strong magnetic exchange interactions in molecular system is another challenge. The exchange interactions through the larger molecular spacers were investigated by Matsuda et al. for various π-conjugated couplers and established a correspondence between electrical conductance and the magnetic exchange interaction. [13] Both the molecular conductance and the exchange interactions decay exponentially with an increase in distance between radical centers. They observed that the increased π-conjugations slow down the decay process. [14,15] The strength of the magnetic exchange coupling constants (2J), mediated through π-conjugated molecular spacers was found to decay exponentially with the length of the couplers. [13] Essentially, the conductance and magnetic coupling (2J) between two spin sources are related through the molecular bridge properties. [16-18] However, in recent years interest has increased in designing and finding molecular candidates that would show an increase in

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“…Undoubtedly, these findings have fully confirmed that molecular vibration could lead to the expected or unexpected effects in charge transfer or other electronic dynamics applications. Furthermore, our group also theoretically demonstrated that molecular inherent vibrations could induce intriguing dynamic diradical character in pentacene, hexazapentacene, and perfluoropentacene . Besides, the β‐turn motifs have been found to be more flexible than the β‐sheet motifs in controlling the efficiency of proton transfer between reactive centers and should also play an intriguing role in assisting charge transfers.…”

Section: Introductionmentioning

confidence: 91%

“…To examine the gradual variations of the relaying properties in vibrational progress of a specific vibrational mode, the dynamic process of a specific vibrational mode is represented by a given number of consecutive snapshots, and hence described by R = R 0 ± n Δ R , where Δ R is an increment of coordinate change and n = 1–10, while + n Δ R and – n Δ R denote the positive and negative shifts, respectively. This method has been proved to be suitable to discussing the vibrational effects in our previous work . Further, the corresponding energies of neutral and anionic distorted and static configurations, spin density distributions, and LUMO and SOMO energies were obtained.…”

Section: Calculational Detailsmentioning

confidence: 99%

Dynamic relaying properties of a β‐turn peptide in long‐range electron transfer

Song

Zhang

2018

J Comput Chem

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The relay stations play a significant role in long-range charge hopping transfer in proteins. Although studies have clarified that many more protein structural motifs can function as relays in charge hopping transfers by acting as intermediate charge carriers, the relaying properties are still poorly understood. In this work, taking a β-turn oligopeptide as an example, we report a dynamic character of a relay with tunable relaying properties using the density functional theory calculations. Our main finding is that a β-turn peptide can serve as an effective electron relay in facilitating long-range electron migration and its relay properties is vibration-tunable. The vibration-induced structural transient distortions remarkably affect the lowest occupied molecular orbital (LUMO) energy, vertical electron affinity and electron-binding mode of the β-turn oligopeptide and the singly occupied molecular orbital (SOMO) energy of the corresponding electron adduct and thus the relaying properties. Different vibration modes lead to different structural distortions and thus have different effects on the relaying properties and ability of the β-turn peptide. For the relaying properties, there approximately is a linear negative correlation of electron affinity with the LUMO energy of the β-turn or the SOMO energy of its electron adduct. Besides, such relaying properties also vary in the vibration evolution process, and the electron-binding modes may be tunable. As an important addition to the known static charge relaying properties occurring in various protein structural motifs, this work reports the dynamic electronrelaying characteristics of a β-turn oligopeptide with variable relaying properties governed by molecular vibrations which can be applied to different proteins in mediating long-range charge transfers. Clearly, this work reveals molecular vibration effects on the electron relaying properties of protein structural motifs and provides new insights into the dynamics of long-range charge transfers in proteins. This is submitted for the J. Comput. Chem. special issue "The Current Status of Computational Chemistry in China" dedicated to Prof. Qianer Zhang for his 90th birthday.

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Molecular Vibrations Induced Potential Diradical Character in Hexazapentacene

Cited by 14 publications

References 60 publications

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

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

Dynamic relaying properties of a β‐turn peptide in long‐range electron transfer

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