Temperature Dependence of Charge-Transfer Fluorescence from Extended and U-shaped Donor−Bridge−Acceptor Systems in Glass-Forming Solvents

Goes, Marijn; Groot, M. de; Koeberg, Mattijs; Verhoeven, J. W.; Lokan, Nigel R.; Shephard, Michael J.; Paddon‐Row, Michael N.

doi:10.1021/jp012507h

Cited by 41 publications

(30 citation statements)

References 48 publications

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“…By choosing appropriate polymers, we can mimic the polarity conditions from ensemble experiments and hence we can tune the energy levels of the LES and the CSS. ZE and PS are the best equivalents in terms of polarity for methylcyclohexane and toluene, respectively (18,19). In ZE, an apolar matrix, we do not expect ET to occur at all.…”

Section: Methodsmentioning

confidence: 80%

Probing conformational dynamics in single donor-acceptor synthetic molecules by means of photoinduced reversible electron transfer

Cotlet

Masuo

Luo

et al. 2004

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

111

102

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S ingle-molecule detection (SMD) has been extensively used to answer questions of both biophysical chemistry and chemical physics relevance (1-5). An elegant way to probe conformational changes is to take advantage of distance-dependent processes involving pairs of fluorophores. Förster resonant energy transfer (FRET) between two fluorophores has gained popularity as a sensitive tool to probe distance changes in the nanometer range (5-8). With an efficiency scaling with the inverse of the 6th power of the interchromophore distance, FRET can be used to track distance changes in the 2-to 8-nm range in various biological structures (5). The distance scale can be downsized to the ångstrom scale if one uses photoinduced electron transfer (ET). ET usually involves a pair of electron donor (D) and acceptor (A) chromophores spatially separated by an edge-toedge distance of Ϸ1 nm or less (9). Because the efficiency scales exponentially with the D-A distance, ET can probe distance changes with subångstrom resolution. However, whereas highly efficient FRET results in fluorescence emitted mainly from the acceptor fluorophore, highly efficient ET usually leads to a strong quenching of the fluorescence of the emitting chromophore. Thus, reports on single-molecule photoinduced ET are rather limited (10-14), in contrast to reports on singlemolecule FRET. A particular situation of ET refers to the case in which the locally excited state (LES) and the charge-separated state (CSS) are relatively close in energy (Fig. 1A, with CSS in position 2). In this case, upon optical excitation, the LES deactivates mainly by forward ET to the CSS and, if the radiationless deactivation of the CSS to the ground state (GS) is inefficient (see below), the CSS is forced to decay through the LES by reverse ET (14, 15). The fluorescence is delayed but can retain a high quantum yield. If present, reversible ET can be probed by SMD if the excited chromophore shows bright fluorescence and high photostability. In some cases, competition between the deactivation of the CSS to the LES or to the GS may be influenced by molecular oxygen (15).Here we use single-molecule fluorescence decay times to probe the dynamics of reversible ET between an excited perylenediimide (acceptor, P) and triphenylamine (donor, N) as parts in a dendritic structure. Triphenylamines are attached to the core perylenediimide by means of a polyphenylene skeleton that imposes some rigidity on the whole structure. The D-A distance is thus modified, in a controlled way, from the first (PN8, Fig. 1B with R ϭ R1) to the second (PN16, Fig. 1B with R ϭ R2) generation; hence, we expected that the parameters of the ET change as well. Materials and MethodsEnsemble stationary and time-resolved fluorescence spectroscopy was performed on 10 Ϫ6 M solutions of PN8 and PN16 (16) in solvents of different polarity: methylcyclohexane, toluene, and ethyl acetate, all of spectral-grade purity. Before measurements, solutions were degassed by freeze-pump-thaw cycling. Fluorescence decays were recorded at 5...

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Section: Methodsmentioning

confidence: 80%

Probing conformational dynamics in single donor-acceptor synthetic molecules by means of photoinduced reversible electron transfer

Cotlet

Masuo

Luo

et al. 2004

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

111

102

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“…Above the melting point of the solvent (at 137 K) the phosphorescence slowly diminishes. In the liquid solvent the CT state is able to relax and emits at longer wavelengths than in the supercooled liquid (temperature region between the melting point and the glass transition temperature at ∼91 K 26) or the glassy matrix. In the liquid solvent also the quantum yield of the CT emission decreases considerably.…”

Section: Resultsmentioning

confidence: 99%

Photophysical properties of the asymmetrically substituted spirobifluorenes spiro‐DPO and spiro‐MeO‐DPO

Brendel

Dias

Saragi

et al. 2009

Physica Status Solidi (a)

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The photophysical behaviour of the oxadiazolyl (PBD) and diphenylamino (TAD) substituted spirobifluorenes 2′,7′‐bis‐(N,N‐diphenylamino)‐2‐(5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazol‐2‐yl)‐9,9′‐spirobifluoren (spiro‐DPO) and 2′,7′‐bis‐(N,N‐diphenylamino)‐2‐(5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazol‐2‐yl)‐9,9′‐spirobifluoren (spiro‐MeO‐DPO) has been investigated by temperature‐dependent steady‐state absorption and luminescence spectroscopy and gated measurements. Fluorescence and phosphorescence lifetime measurements, relative quantum yields and dipole moments of the excited states have been determined. Asymmetrically substituted spirobifluorenes exhibit charge‐transfer (CT) emission due to coupling (spiroconjugation) between the fluorene fragments of spirobifluorene. They show a considerable ground‐state dipole moment and exist as equilibrating conformeres. Population of the CT state only occurs after absorption to the locally excited singlet state. The CT fluorescence is dominated by the emission of two equilibrating conformeres with similar dipole moments. At low temperature they planarize in both molecular halves and show strong phosphorescence that is still detectable at room temperature.

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“…For electronic transitions in molecules dissolved in condensed-phase solvents, emission energies are strongly affected by freezing of the solvent orientational polarization through liquid crystallization or glass transition. [17][18][19][20][21][22] Although some of these effects can be related to the drop of the dielectric constant when a polar fluid freezes, 17,[23][24][25] the effect of freezing on ET reactions is actually dynamic in nature. 20,22,[25][26][27] Slow solvent modes may not achieve equilibrium on the time scale of ET ͑Refs.…”

Section: Introductionmentioning

confidence: 99%

Solvent reorganization of electron transitions in viscous solvents

Ghorai¹,

Matyushov²

2006

The Journal of Chemical Physics

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We develop a model of electron transfer reactions at conditions of nonergodicity when the time of solvent relaxation crosses the observation time window set up by the reaction rate. Solvent reorganization energy of intramolecular electron transfer in a charge-transfer molecule dissolved in water and acetonitrile is studied by molecular dynamics simulations at varying temperatures. We observe a sharp decrease of the reorganization energy at a temperature identified as the temperature of structural arrest due to cage effect, as discussed by the mode-coupling theory. This temperature also marks the onset of the enhancement of translational diffusion relative to rotational relaxation signaling the breakdown of the Stokes-Einstein relation. The change in the reorganization energy at the transition temperature reflects the dynamical arrest of the slow, collective relaxation of the solvent related to the relaxation of the solvent dipolar polarization. An analytical theory proposed to describe this effect agrees well with both the simulations and experimental Stokes shift data. The theory is applied to the analysis of charge-transfer kinetics in a low-temperature glass former. We show that the reorganization energy is substantially lower than its equilibrium value for the low-temperature portion of the data. The theory predicts the possibility of discontinuous changes in the dependence of the electron transfer rate on the free energy gap when the reaction switches between ergodic and nonergodic regimes.

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Temperature Dependence of Charge-Transfer Fluorescence from Extended and U-shaped Donor−Bridge−Acceptor Systems in Glass-Forming Solvents

Cited by 41 publications

References 48 publications

Probing conformational dynamics in single donor-acceptor synthetic molecules by means of photoinduced reversible electron transfer

Probing conformational dynamics in single donor-acceptor synthetic molecules by means of photoinduced reversible electron transfer

Photophysical properties of the asymmetrically substituted spirobifluorenes spiro‐DPO and spiro‐MeO‐DPO

Solvent reorganization of electron transitions in viscous solvents

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