Lowest Charge Transfer Excited State Research Articles

External electric field manipulating sequential and super-exchange charge transfer in donor-bridge-acceptor system in two-photon absorption

In this paper, we report external electric field manipulates sequential and super-exchange charge transfer in donor-bridge-acceptor (D-B-A) system in two-photon absorption (TPA). Our results reveal that the orientation and absorption strength of sequential and super-exchange charge transfer excitons can be well manipulated in D-B-A system in TPA. The energy levels and absorption intensity of electronic transitions in one-photon absorption (OPA), as the intermediate state in TPA, are strongly influenced by external electric field, which provides a great opportunity for strong absorption with different charge transfer characteristics in TPA of D-B-A. Also, the optical properties of lowest charge transfer excited state under different external electric fields are also investigated in OPA. Our results can provide deeper understanding of external electric field in controlling sequential and super-exchange charge transfer in D-B-A system in TPA.

Charge and energy transfer in a bithiophene perylenediimide based donor–acceptor–donor system for use in organic photovoltaics

The elementary charge and excitation energy transfer steps in a novel symmetric donor-acceptor-donor triad first described in Roland et al. Phys. Chem. Chem. Phys., 2012, 14, 273, consisting of a central perylenediimide moiety as a potential electron acceptor and two identical electron rich bithiophene compounds, have been investigated using quantum chemical methodology. These elementary processes determine the applicability of such systems in photovoltaic devices. The molecular structure, excited states and the photo-physical properties are investigated using smaller model systems and including solvation effects. The donor and acceptor π-systems are separated by an ethyl bridge such that the molecular orbitals are either located on the donor or acceptor moiety making the identification of locally excited versus charge transfer states straightforward. Using excited state geometry optimizations, the mechanism of photo-initiated charge separation could be identified. Geometry relaxation in the excited donor state leads to a near-degeneracy with the locally excited acceptor state, entailing strong excitonic coupling and resonance energy transfer. This energy transfer process is driven by planarization and bond length alternation of the donor molecule. Geometry relaxation of the locally excited acceptor state in turn reveals a crossing with the energetically lowest charge transfer excited state. The energetic position of the latter depends in a sensitive fashion on the solvent. This provides an explanation of the sequential process observed in the experiment, favoring ultrafast (∼130 fs) formation of the excited acceptor state followed by slower (∼3 ps scale) formation of the charge separated state.

Revisiting Molecular Dissociation in Density Functional Theory: A Simple Model.

A two-electron one-dimensional model of a heteroatomic molecule composed of two open-shell atoms is considered. Including only two electrons isolates and examines the effect that the highest occupied molecular orbital has on the Kohn-Sham potential as the molecule dissociates. We reproduce the characteristic step and peak that previous high-level wave function methods have shown to exist for real molecules in the low-density internuclear region. The simplicity of our model enables us to investigate in detail their development as a function of bond-length, with little computational effort, and derive properties of their features in the dissociation limit. We show that the onset of the step is coincident with the internuclear separation at which an avoided crossing between the ground-state and lowest charge-transfer excited-state is approached. Although the step and peak features have little effect on the ground-state energetics, we discuss their important consequences for dynamics and response.

ChemInform Abstract: Structure‐Magnetic Coupling Relationships for Metallocene Acceptor Based Charge‐Transfer Complexes

ChemInformVolume 21, Issue 19 Reviews ChemInform Abstract: Structure-Magnetic Coupling Relationships for Metallocene Acceptor Based Charge-Transfer Complexes J. S. MILLER, J. S. MILLER Exp. Stn., E. I. du Pont de Nemours&Co., Inc., Wilmington, DE 19880-0328, USASearch for more papers by this authorA. J. EPSTEIN, A. J. EPSTEIN Exp. Stn., E. I. du Pont de Nemours&Co., Inc., Wilmington, DE 19880-0328, USASearch for more papers by this author J. S. MILLER, J. S. MILLER Exp. Stn., E. I. du Pont de Nemours&Co., Inc., Wilmington, DE 19880-0328, USASearch for more papers by this authorA. J. EPSTEIN, A. J. EPSTEIN Exp. Stn., E. I. du Pont de Nemours&Co., Inc., Wilmington, DE 19880-0328, USASearch for more papers by this author First published: May 8, 1990 https://doi.org/10.1002/chin.199019325Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume21, Issue19May 8, 1990 RelatedInformation

Organometallic ferromagnets

Some organometallic solids comprising linear chains of alternating m 8 = 1/2 metallocenium donors, D, and cyanocarbon acceptors, A, i.e. ••• D +*A~*D+*A- * •••, exhibit cooperative magnetic phenomena, i.e. ferro-, antiferro-, ferri-, and meta-magnetism. For [Fe II (C 5 Me 5 ) 2 ]+*[T C N E ]- (Me = methyl; T C N E = tetracyanoethylene) bulk ferromagnetic behaviour is observed below the Curie temperature of 4.8 K. Replacement of Fe III with Fe II , Ni III and Cr III leads to complexes with dia-, antiferro- and ferrimagnetic behaviour, respectively. These results are consistent with a model of configuration mixing of the lowest charge transfer excited state with the ground state developed earlier to understand the magnetic coupling of such systems. The model predicts the magnetic coupling as a function of electron configuration and direction of charge transfer (retro or reverse) and is a useful guide to designing new organic and /or organometallic complexes with cooperative magnetic coupling. To test the model and identify new materials with ferromagnetic coupling new TCNE-based electron transfer salts were prepared.

Structure-Magnetic Coupling Relationships for Metallocene-Acceptor Based Charge Transfer Complexes

Abstract The electron transfer complex [FeIII(C5Me5)2]·+[TCNE]·− (TCNE = tetracyanoethylene) is a bulk ferromagnet below the Curie temperature of 4.8 K. The deliberate synthesis of additional bulk ferromagnets via the selective i) replacement of the metal ion, ii) replacement of Me substitutent groups with H, iii) use of C6-ring ligands instead of C5-ring ligands, and iv) replacement of TCNE with alternate acceptors has been carried out. Although several systems exhibit ferromagnetic coupling, a second bulk ferromagnet has not been identified. Replacement of FeIII with CrIII, NiIII, and FeII leads to complexes with antiferromagnetic coupling, ferrimagnetic behavior, and almost no magnetic interaction, respectively. These resulfs are consistent with a model of configuration mixing of the lowest charge transfer excited state with the ground state developed earlier to understand the magnetic coupling in such systems. The model predicts the magnetic coupling as a function of electron configuration and direction of charge transfer and is a useful guide to design new organic and/or organometallic complexes with cooperative magnetic coupling.

Photolytic and radiolytic studies of tris(2,2'-bipyridine)ruthenium(2+) in micellar solutions

Ru(bpy)/sub 3//sup 2 +/ is shown to form a water-insoluble salt with dodecyl sulfate ions (DS) which is solubilized by sodium dodecyl sulfate (SDS) micelles. In the micelles the rate of the reaction of Ru(bpy)/sub 3//sup 2 +/ with e/sup -//sub aq/ is reduced while its rate of reaction with various metal cations in their reduced form (Zn/sup +/, Cd/sup +/, Co/sup +/) is enhanced. This, as well as the ionic strength effect on these rates, clearly indicates that Ru(bpy)/sub 3//sup 2 +/ resides in a negatively charged ionic atmosphere. In the presence of SDS micelles the luminescence from the charge transfer excited state of Ru(bpy)/sub 3//sup 2 +/ is red shifted as compared to its spectrum in the absence of SDS. Since long-chain alcohols have a similar effect it is concluded that Ru(bpy)/sub 3//sup 2 +/ must strongly interreact with the hydrocarbon chain of the surfactant. Our kinetic results indicate that essentially all of the Ru(bpy)/sub 3//sup 2 +/ is bound to the micelles under our experimental conditions. The rates of reaction of the lowest charge transfer excited state of Ru(bpy)/sub 3//sup 2 +/ in micellar solutions are shown to be faster with Cu/sup 2 +/ ions and slowermore » with Fe(CN)/sub 6//sup 3 -/ ions as compared to the rates of the same reactions in simple aqueous solutions. However, the yield of the redox products of the reaction with Cu/sup 2 +/ that can escape to the bulk of the solution is greatly reduced by the micelles.« less