Photophysics and Mechanisms of Intramolecular Electronic Energy Transfer in Bichromophoric Molecular Systems:  Solution and Supersonic Jet Studies

Speiser, Shammai

doi:10.1021/cr941193+

Cited by 432 publications

(344 citation statements)

References 421 publications

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“…At the immediate vicinity of either of the two configurations of the nuclei, the motion is bounded, but larger-amplitude motion can connect the two hollows. Major intramolecular charge reorganization follows upon a change in nuclear geometry (4)(5)(6)(7)(8). The time scale of the charge shuffling is that of the motion of the nuclei relocating between the two configurations.…”

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confidence: 99%

An electronic time scale in chemistry

Remacle

Levine

2006

Proc. Natl. Acad. Sci. U.S.A.

396

335

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Ultrafast, subfemtosecond charge migration in small peptides is discussed on the basis of computational studies and compared with the selective bond dissociation after ionization as observed by Schlag and Weinkauf. The reported relaxation could be probed in real time if the removal of an electron could be achieved on the attosecond time scale. Then the mean field seen by an electron would be changing rapidly enough to initiate the migration. Tyrosine-terminated tetrapeptides have a particularly fast charge migration where in <1 fs the charge arrives at the other end. A femtosecond pulse can be used to observe the somewhat slower relaxation induced by correlation between electrons of different spins. A slower relaxation also is indicated when removing a deeper-lying valence electron. When a chromophoric amino acid is at one end of the peptide, the charge can migrate all along the peptide backbone up to the N end, but site-selective ionization is probably easier to detect for tryptophan than for tyrosine.attosecond lasers ͉ charge transfer ͉ protein mass spectrometry A chemical rearrangement occurs when atoms in a molecule change their specific arrangement. The time scale of chemistry is therefore the time scale for the motion of atoms (1, 2). The forces operating on the atoms determine the path of this motion. In the Born-Oppenheimer approximation, it is the averaging over the much faster motion of the electrons that specifies the potential energy and hence the forces. The physical picture for this approximation is that the electrons instantly adjust to the current position of the nuclei so that the equilibrium arrangement of the bonded atoms is determined as a minimum of the electronic energy. In the Born-Oppenheimer approximation, the system is confined to be in a single stationary electronic state, and if this confinement is strict then there is no electronic time scale that is relevant to chemistry. During a chemical rearrangement, the motion of the atoms can be accompanied by a reorganization of the electronic structure, and recent experimental progress allows for probing this change (3) in real time. However, it is the motion of the nuclei that sets the time scale because the electronic reorganization exactly tracks the shifts in the positions of the nuclei. As the heavier nuclei move, the light electrons immediately adapt.It is recognized that the energy of the same stationary electronic state can have two distinct minima, where the electronic charge distribution has a quite different character. At the immediate vicinity of either of the two configurations of the nuclei, the motion is bounded, but larger-amplitude motion can connect the two hollows. Major intramolecular charge reorganization follows upon a change in nuclear geometry (4-8). The time scale of the charge shuffling is that of the motion of the nuclei relocating between the two configurations.Optical excitation can prepare a nonstationary state, and such a state is often known as the optically bright state. The optically bright state is not sta...

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confidence: 99%

An electronic time scale in chemistry

Remacle

Levine

2006

Proc. Natl. Acad. Sci. U.S.A.

396

335

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“…The spacer of C-5, M-5, and N-5 should be short enough to keep the two chromophores from close contact and thus intramolecular electronic energy transfer (EET) will predominate. 10 Since the quencher-fluorophore distance is constant (n = 5), the main factor of intra-EET will be the overlap integral, J. The shortest absorption λ max and the lowest ε of carbazole imply that the carbazole-fluorescein pair will minimize the overlap integral, J, and suppress the selfquenching most effectively.…”

Section: Notesmentioning

confidence: 99%

Self-quenching Mechanism: the Influence of Quencher and Spacer on Quencher-fluorescein Probes

Kim¹,

Park²,

Hong

2007

Bulletin of the Korean Chemical Society

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Fluorescent chemosensors provide an extremely sensitive optical method for the real-time monitoring of molecular recognition events. An understanding of the fluorescent on/ off mechanism is essential for the rational design of fluorescent chemosensors. The majority of fluorescent chemosensors working in aqueous media operate by one of three mechanisms: (1) the suppression of photoinduced electron transfer (PET); (2) alteration of the microenvironment of a solvatochromic fluorophore; and (3) modulation of the fluorescence resonance energy transfer (FRET) between two fluorophores.1 The first two mechanisms are suitable for small molecule sensing (e.g., cations, small organic compounds, etc.), but FRET is very useful in the biopolymer state, for its distance information can be obtained in the 10 to 100 Å region.2 In spite of the excellent applications of FRET for biomolecule sensing (c-AMP, insulin, etc.), the operations depend on a complicated biological pathway. 3Peptides with an FRET pair have been used as monitoring probes for a given enzyme activity. However, in various fluorophore pairs that have been examined, FRET peptide probes did not operate properly i.e., they were self-quenched. 4 This self-quenching can be explained in terms of an intramolecular ground-state dimer complex between the FRET fluorophore pair in an aqueous solution. 5 The strength of the aggregation between the two dye molecules depends on the molecular structure, solvent, temperature, and the presence or absence of electrolytes. 6Our aim is to systematically study the self-quenching mechanism for covalently linked fluorophore pairs. For simplicity, the factors influencing the efficiency of selfquenching are disassembled into four components ( Figure 1). A FRET pair was replaced by a quencher-fluorophore pair as the reporting group. This overcomes the restriction for the FRET donor-acceptor resonance condition.7 From a practical viewpoint, water and fluorescein were chosen as the solvent and fluorophore, respectively; water is a crucial solvent for physiological systems; furthermore, fluorescein has a high fluorescence quantum yield in aqueous solution and its synthetic handling has been well established.As the quencher part, carbazole, methyl red and 1,8-naphthalimide were selected. The effect of the spacer can be controlled by varying the alkyl chain length (-(CH 2 ) n -, n = 5, 11, 15) and a flexible tetraethylene glycol unit (Figure 2). At pH 7.5 (50 mM HEPES buffer, I = 0.1 (NaNO 3 )), the fluorescence emission of C-n (n = 5, 11, 15) and C-TE ([probes] = 1 μM) was measured (Figure 3). 8 It has been reported that there are two opposing factors determining the stability of aggregates of the derivatives containing two Rose Bengal moieties: the longer the chain, the easier it is to

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“…Optical spectroscopy is an important tool in the study of photophysics and photochemistry 8 , charge and energy transfer 9 , intermolecular interactions and bonding in these systems. The theoretical investigation is complicated by the delocalized nature of electronic excitations, strong electron correlations, and vibronic coupling.…”

Section: Introductionmentioning

confidence: 99%

Localized and Delocalized Electronic Excitations in Biological and Artificial Antenna Complexes

Tretiak¹,

Middleton²,

Chernyak³

et al. 2000

Photoinduced Charge Transfer

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The Collective Electronic Oscillators (CEO) approach based on the Time-Dependent Hartree-Fock approximation is applied to analyze localization and delocalization of electronic excitations, charge and energy transfer in LH2 aggregates (biological antenna complexes) and in phenylacetylene dendrimers (artificial antenna macromolecules). Two-dimensional analysis of transition density matrices indicates that electron-hole pairs created upon optical excitation in LH2 aggregate are localized within separate chromophores. In addition LH2 has a band of low-lying charge-transfer states unaccessible with linear absorption spectroscopy. In phenylacetylene dendrimers, electronic excitation are shown to be localized within linear segments connected by benzene rings substituted at the meta-position. These results are used to construct effective Frenkel exciton hamiltonians in these biological and artificial light-harvesting antenna complexes.

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Photophysics and Mechanisms of Intramolecular Electronic Energy Transfer in Bichromophoric Molecular Systems: Solution and Supersonic Jet Studies

Cited by 432 publications

References 421 publications

An electronic time scale in chemistry

An electronic time scale in chemistry

Self-quenching Mechanism: the Influence of Quencher and Spacer on Quencher-fluorescein Probes

Localized and Delocalized Electronic Excitations in Biological and Artificial Antenna Complexes

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