Effect of charge delocalization on radical ion pair electronic coupling

Sinks, Louise E.; Weiss, Emily A.; Giaimo, Jovan M.; Wasielewski, Michael R.

doi:10.1016/j.cplett.2005.01.093

Cited by 16 publications

(18 citation statements)

References 35 publications

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“…Photogenerated D + -B-A - biradicals have been used to probe structural effects on electron transfer rates through correlating the magnetic exchange interaction, J , with the electronic coupling matrix element H ab . 1,16,18-21 These data show that ET rates through phenyl bridges possess exponential distance dependence with β ~ 0.5, in excellent agreement with theory and direct electron transfer rate studies. Recently, we showed that covalently linked, nondisjoint heterospin triplet D-A biradicals (Fig.…”

Section: Introductionsupporting

confidence: 79%

Spectroscopic Studies of Bridge Contributions to Electronic Coupling in a Donor-Bridge-Acceptor Biradical System

et al. 2012

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Variable temperature electronic absorption and resonance Raman spectroscopies are used to probe the excited state electronic structure of TpCum,MeZn(SQ-Ph-NN) (1) – a donor-bridge-acceptor (D-B-A) biradical complex and a ground state analog of the charge-separated excited state formed in photoinduced electron transfer reactions. Strong ferromagnetic exchange coupling that is mediated by the para-phenylene bridge stabilizes the triplet ground state of this molecule. Detailed spectroscopic and bonding calculations elucidate key bridge distortions that are involved in the SQ(π)SOMO→NN-Ph (π*)LUMO D→A charge transfer (CT) transition. We show that the primary excited state distortion that accompanies this CT is along a vibrational coordinate best described as a symmetric Ph(8a)+SQ(in-plane) linear combination and underscores the dominant role of the phenylene bridge fragment acting as an electron acceptor in the D-B-A charge transfer state. Our results show the importance of the localized phenylene bridge LUMO wavefunction in promoting (1) electron transfer in D-Ph-A systems, and (2) electron transport in biased electrode devices that employ a 1,4-phenylene linkage. We have also developed a relationship between the spin density on the acceptor, as measured via the isotropic NN nitrogen hyperfine interaction, and the strength of the D→A interaction given by the magnitude of the electronic coupling matrix element, Hab.

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Section: Introductionsupporting

confidence: 79%

Spectroscopic Studies of Bridge Contributions to Electronic Coupling in a Donor-Bridge-Acceptor Biradical System

et al. 2012

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“…The solvent molecules can be particularly significant because they can mediate the interaction between the unpaired electrons on each radical in a process known as superexchange. A few attempts have been made to perform such calculations [46] and to compare experimental and theoretical results in solid-state lophyl RPs [48] and in linked donor-acceptor diad compounds [49]. A full understanding of the RP exchange interaction is still awaited.…”

Section: Magnetic Field Effects In Chemical Systems 25mentioning

confidence: 99%

Magnetic field effects in chemical systems

Rodgers

2009

Pure and Applied Chemistry

180

205

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Chemical reactions that involve radical intermediates can be influenced by magnetic fields, which act to alter their rate, yield, or product distribution. These effects have been studied extensively in liquids, solids, and constrained media such as micelles. They may be interpreted using the radical pair mechanism (RPM). Such effects are central to the field of spin chemistry of which there have been several detailed and extensive reviews. This review instead presents an introductory account of the field of spin chemistry, suitable for use by graduate students or researchers who are new to the area. It proceeds by giving a brief historical overview of the development of spin chemistry, before introducing the essential theory. This is then illustrated by application to a series of recent developments in solution-phase magnetic field effects (MFEs). The closing pages of this review describe the role played by spin chemistry in the remarkable magnetic compass sense of birds and other animals.

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“…Apart from thermodynamic considerations, there are other possible ways to decrease the rate of charge recombination in simple molecular dyads . For example, concepts based on spin restriction rules, conformational gating, applied magnetic fields, orientational effects, and orbital symmetry have been considered as ways to avoid the time-consuming synthesis needed to produce the multicomponent arrays. The effects of these approaches tend to be limited and/or of restricted applicability .…”

Section: Introductionmentioning

confidence: 99%

Charge Shift and Triplet State Formation in the 9-Mesityl-10-methylacridinium Cation

et al. 2005

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The target donor-acceptor compound forms an acridinium-like, locally excited (LE) singlet state on illumination with blue or near-UV light. This LE state undergoes rapid charge transfer from the acridinium ion to the orthogonally sited mesityl group in polar solution. The resultant charge-transfer (CT) state fluoresces in modest yield and decays on the nanosecond time scale. The LE and CT states reside in thermal equilibrium at ambient temperature; decay of both states is weakly activated in fluid solution, but decay of the CT state is activationless in a glassy matrix. Analysis of the fluorescence spectrum allows precise location of the relevant energy levels. Intersystem crossing competes with radiative and nonradiative decay of the CT state such that an acridinium-like, locally excited triplet state is formed in both fluid solution and a glassy matrix. Phosphorescence spectra position the triplet energy well below that of the CT state. The triplet decays via first-order kinetics with a lifetime of ca. 30 micros at room temperature in the absence of oxygen but survives for ca. 5 ms in an ethanol glass at 77 K. The quantum yield for formation of the LE triplet state is 0.38 but increases by a factor of 2.3-fold in the presence of iodomethane. The triplet reacts with molecular oxygen to produce singlet molecular oxygen in high quantum yield. In sharp contradiction to a recent literature report, there is no spectroscopic evidence to indicate the presence of an unusually long-lived CT state.

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Effect of charge delocalization on radical ion pair electronic coupling

Cited by 16 publications

References 35 publications

Spectroscopic Studies of Bridge Contributions to Electronic Coupling in a Donor-Bridge-Acceptor Biradical System

Spectroscopic Studies of Bridge Contributions to Electronic Coupling in a Donor-Bridge-Acceptor Biradical System

Magnetic field effects in chemical systems

Charge Shift and Triplet State Formation in the 9-Mesityl-10-methylacridinium Cation

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