Long-range, photoinduced charge separation in solvent-free donor—bridge—acceptor molecules

Jortner, Joshua; Bixon, M.; Wegewijs, B.; Verhoeven, J. W.; Rettschnick, R.P.H.

doi:10.1016/0009-2614(93)87150-2

Cited by 49 publications

(41 citation statements)

References 15 publications

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“…In this case charge transfer becomes a pure intramolecular relaxation process [12][13][14][15] similar to internal conversion 14,15 taking place between two electronic states located at different sites of the molecule. The theoretical description leads to an energy gap law for the charge-transfer rate 15 similar to that found for internal conversion.…”

Section: Introductionmentioning

confidence: 99%

Highly Efficient Charge Transfer in Peptide Cations in the Gas Phase: Threshold Effects and Mechanism

Weinkauf¹,

Schanen²,

Metsala³

et al. 1996

J. Phys. Chem.

196

238

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We present new experimental data demonstrating specific, photoactivated positive charge migration in isolated peptide radical cations. The effect exhibits a threshold behavior, which we can directly correlate with energetics of local electronic states. A new very efficient mechanism for charge transfer in cations is proposed that involves an extended coulomb state (EC) of shakeup character. Our investigations are performed on laserdesorbed, cooled, neutral peptides in the gas phase. Charge localization in the peptide is achieved by resonant UV two-photon ionization at an aromatic chromophore. Charge flow in the cations can be activated by absorption of a first visible (VIS) photon. Presence of charge in the aromatic chromophore is probed by resonant absorption of a second VIS photon and monitored by dissociation. While this charge detection is found to work in isolated, positively charged chromophores or amino acids, it is efficiently quenched in some peptides. We explain this by photoactivated charge transfer and charge storage in nonaromatic groups of the peptides. At threshold this process is found to be strongly dependent on amino acid substitution even far away from the site of photoactivation. For analysis we first set up a local molecular orbital model for peptide cations and subsequently obtain a landscape of local electronic cation states formed by local hole and low-lying extended coulomb states. Charge transfer is found to be a through-bond mechanism involving energetically accessible electronic states along the path of charge flow. Charge transfer between hole states is mediated with very high efficiency through saturated carbon bridges by extended coulomb states. This new mechanism seems to be generally applicable to large extended molecular radical cations. Only barriers of the size of a full length of a certain defined amino acid are found to block charge transfer. The model qualitatively accounts for the order of the rates of the processes involved.

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Section: Introductionmentioning

confidence: 99%

Highly Efficient Charge Transfer in Peptide Cations in the Gas Phase: Threshold Effects and Mechanism

Weinkauf¹,

Schanen²,

Metsala³

et al. 1996

J. Phys. Chem.

196

238

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“…demonstrate that extended TB-TEX formation is an efficient deactivation pathway for 3 NPT* in the investigated linked systems 1a,b. The rate constant of this process was even higher than through space exciplex formation in 6, where the chromophores are directly linked.…”

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confidence: 66%

“…Thus, LFP of 1a with selective excitation of BZP at 355 nm, gave rise to transient absorption spectra where contribution of the BZP triplet excited state ( 3 BZP*, max ca. 530 nm) was almost negligible, yet 3 NPT* (max = 420 nm) was the predominating species as early as 20 ns after the laser pulse (Figure 3, left). This indicates a very fast TB-TTET from BZP to NPT in this system.…”

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confidence: 99%

“…[22][23][24] Exciplex formation constitutes an alternative channel for excited states deactivation, 1 whose involvement has been reported in the intramolecular singlet quenching of flexible systems. 3,4,[25][26][27][28] Interestingly, several examples have been reported, in which photoinduced electron transfer in D-A systems linked through a rigid bridge leads to 'exciplex' type fluorescence, more appropriately referred to as extended charge separated state. [29][30][31][32][33][34][35] Moreover, triplet exciplex formation has been investigated in flexible benzophenone (BZP)/naphthalene (NPT) bichromophoric systems, in which decay of 3 NPT* occurs through intramolecular exciplex formation with ground state BZP.…”

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confidence: 99%

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Triplet energy management between two signaling units through cooperative rigid scaffolds

et al. 2016

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Through-bond triplet exciplex formation in donor-acceptor systems linked through a rigid bile acid scaffold has been demonstrated on the basis of kinetic evidence upon population of the triplet acceptors (naphthalene, or biphenyl) by through-bond triplet-triplet energy transfer from benzophenone.Energy and electron transfer (ET and et, respectively) are two general non-radiative pathways in the quenching of a triplet excited state, 1 which require effective orbital overlap within the van der Waals radii of donor (D) and acceptor (A) chromophores.2 Actually, it is well established that kET drops to negligible small values when the D-A distance is longer than 5-10 Å.1 When D and A are linked by a spacer, triplet-triplet energy transfer (TTET) could proceed through-space or through-bond (TB) mechanisms depending on the nature of the bridge. In flexible bridge-linked D-A systems, a rapid conformational equilibrium leads to spatial arrangements, in which the two chromophores are close enough for orbital overlap within the lifetime of the donor triplet, so that TTET happens through-space. [3][4][5][6][7][8][9][10][11] Conversely, in the case of rigid saturated hydrocarbon bridges, in which D and A distances are substantially longer than the sum of the van der Waals radii, TB mechanism is largely predominating.12-21 In these systems, the observed TTET happening TB is facilitated by the  and * orbitals of the bridge and, in general, is strongly dependent on the conformations. 22-24Exciplex formation constitutes an alternative channel for excited states deactivation, 1 whose involvement has been reported in the intramolecular singlet quenching of flexible systems. 3,4,[25][26][27][28] Interestingly, several examples have been reported, in which photoinduced electron transfer in D-A systems linked through a rigid bridge leads to 'exciplex' type fluorescence, more appropriately referred to as extended charge separated state. [29][30][31][32][33][34][35] Moreover, triplet exciplex formation has been investigated in flexible benzophenone (BZP)/naphthalene (NPT) bichromophoric systems, in which decay of 3 NPT* occurs through intramolecular exciplex formation with ground state BZP. [36][37][38] To our knowledge, the possibility of TB triplet exciplex (TB-TEX) formation in D-A systems linked through a rigid bridge has not yet been explored. Herein, this issue has been addressed by means of a novel approach based on a 'tandem' TB-TTET with subsequent formation of a TB extended exciplex from the triplet Figure S1 in the ESI); the same was true for 6 and 7, lacking the LA spacer. These observations indicate the absence of significant ground state interactions between the donor and acceptor units. The phosphorescence spectra of 1a and 1b in ethanol at 77 K upon BZP excitation at 355 nm were coincident with that of 3a

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“…[ 10,11 ], but even under fully isolated conditions, the D-br-A molecules 1-3 are capable of long-range charge separation after photoexcitation of the accepter chromophorc, without the need for strong internal reorganization [ 15].…”

Section: Wavelength (Nmlmentioning

confidence: 99%

Photoinduced electron transfer in isolated bichromophoric and solvated trichromophoric systems

Verhoeven

Wegewijs

Hermant

et al. 1996

Journal of Photochemistry and Photobiology A: Chemistry

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General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. AbstractAtler local photoexci|ation of the accepter chmmophore, fast and virtually barrierless charge separation over approximately 5 A is observed under supersonic jet isolated conditions in three rigid donor-bridge-accepter (D-br-A) systems in which D and A are separated by three o' bonds. It is suggested that low frequency tntramolecular vibrational modes, discernible in the well-resolved excitation spectra, play a role in enabling efficient internal conversion between the locally excited and charge transfer states.Insertion of an extra piperidine unit in the bridge elongates its overall length to seven o" bonds, while at the same time a tertiary nitrogen is added as an intermediate donor site. In the resulting trichromophoric systems (D2-br-Dt-br-A). stepwise charge separation occur= in salution with a strong solvent dependence.

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Long-range, photoinduced charge separation in solvent-free donor—bridge—acceptor molecules

Cited by 49 publications

References 15 publications

Highly Efficient Charge Transfer in Peptide Cations in the Gas Phase: Threshold Effects and Mechanism

Highly Efficient Charge Transfer in Peptide Cations in the Gas Phase: Threshold Effects and Mechanism

Triplet energy management between two signaling units through cooperative rigid scaffolds

Photoinduced electron transfer in isolated bichromophoric and solvated trichromophoric systems

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