Ultrafast Dynamics of Pyrene Excimer Formation in Y Zeolites

Cheng, Karen A. W. Y.; Schepp, Norman P.; Cozens, Frances L.

doi:10.1021/jp046935+

Cited by 17 publications

(17 citation statements)

References 31 publications

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“…At the low probe energies chosen to suppress dissociative photoionization, the ionization probability of vibrationally excited dimers is reduced, leading to a decreasing dimer ion signal. Interestingly similar time constants as in the present work were observed for emission changes from zeolite-incorporated pyrene (7-13 ps), 49 and in pyrene-doped polymers (4-10 ps). 50 In both cases these contributions were assigned to excimer formation in the respective systems.…”

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confidence: 89%

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

Hoche

Schmitt

Humeniuk

et al. 2017

Phys. Chem. Chem. Phys.

135

125

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a These authors contributed equally to the work. AbstractThe understanding of excimer formation in organic materials is of fundamental importance, since it profoundly influences their functional performance in applications such as light-harvesting, photovoltaics or organic electronics. We present a joint experimental and theoretical study of the ultrafast dynamics of excimer formation in the pyrene dimer, which is the archetype of an excimer forming system. We perform simulations of the nonadiabatic photodynamics in the frame of TDDFT that reveal two distinct excimer formation pathways in the gas-phase dimer. The first pathway involves local excited state relaxation close to the initial Frank-Condon geometry that is characterized by a strong excitation of the stacking coordinate exhibiting damped oscillations with a period of 350 fs that persist for at least 5 ps. The second excimer forming pathway involves large amplitude oscillations along the parallel shift 1 coordinate with a period of ≈ 900 fs that after intramolecular vibrational energy redistribution on a 2 ps time scale leads to the formation of a perfectly stacked dimer.The electronic relaxation within the excitonic manifold is mediated by the presence of conical intersections formed between fully delocalized excitonic states. Such conical intersections may generally arise in stacked π-conjugated aggregates due to the interplay between the long-range and short-range electronic coupling. The simulations are supported by picosecond photoionization experiments in a supersonic jet that provide a time-constant for the excimer formation of around 6-8 ps, in excellent agreement with theory. Finally, in order to explore how the crystal environment influences the excimer formation dynamics we perform large scale QM/MM nonadiabatic dynamics simulations on a pyrene crystal in the framework of the tight-binding TDDFT. In contrast to the isolated dimer, the excimer formation in the crystal follows a single reaction pathway in which the initially excited parallel slip motion is strongly damped by collisions with the surrounding molecules leading to the slow excimer stabilization with a time constant of several picoseconds.2

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supporting

confidence: 89%

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

Hoche

Schmitt

Humeniuk

et al. 2017

Phys. Chem. Chem. Phys.

135

125

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“…who, in a DFT approach, proposed that the formula [Fe II (H 2 O) 5 (NO 0 )] 2+ was more appropriate. In the same work, they stressed the linearity of the Fe‐N‐O moiety in 1 ’s ground state . In 2010, the Ghosh group also reported a linear FeNO entity and alluded to the unusually flat bending potential of the triatomic group .…”

Section: Figurementioning

confidence: 99%

“…In detail, the NO moiety carries the following charge, depending on the given procedure: −0.10 (QTAIM), +0.09 (NPA), +0.19 (ECDA), −0.05 (IAO/IBO), +0.18 (Mulliken), all from BP86/def2‐TZVP data, +0.06 (Mulliken) from CASSCF(9,13) data. At first glance, the most recently published Fe II (NO 0 ) formulation thus appears in line with those calculations . In fact, there was a tendency in the past to interpret oxidation states as “real” charges.…”

Section: Figurementioning

confidence: 99%

[Fe(H₂O)₅(NO)]²⁺, the “Brown‐Ring” Chromophore

Monsch

Klüfers

2019

Angew Chem Int Ed

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Although the “brown‐ring” ion, [Fe(H2O)5(NO)]2+ (1), has been a research target for more than a century, this poorly stable species had never been isolated. We now report on the synthesis of crystals of a salt of 1 which allowed us to tackle the unique bonding situation on an experimental basis. As a result of the bonding analysis, two stretched, spin‐polarised π‐interactions provide the Fe–NO binding—and challenge the concept of “oxidation state”.

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“…One way to differentiate between these two possibilities is by ultrafast time‐resolved fluorescence measurements, where the formation of the pyrene excimer emission is probed as a function of time. Recently, we reported preliminary results from measurements of excimer emission rise times of pyrene incorporated into Y zeolites on the low‐picosecond timescale with the use of an ultra‐fast streak camera (24). In this article, we present the full results of the study, including the variation of these rise times as a function of zeolite, sealing technique and coincorporated solvents.…”

Section: Introductionmentioning

confidence: 99%

Resolution of Ultrafast Pyrene Excimer Emission Rise Times in Zeolites X and Y†

Cheng

Schepp

Cozens

2006

Photochem Photobiol

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Pyrene has been a favorite photophysical probe molecule for zeolite research because of its ability to exhibit both monomer and excimer emission upon excitation. This study combines the use of ultrafast time-resolved fluorescence spectroscopy with steady-state fluorescence spectroscopy to study the excimer emission of pyrene incorporated within zeolites LiY, NaY, KY and NaX. The effects of sealing technique and coincorporated solvents are also explored. Pyrene excimer emission is resolvable with the use of an ultrafast streak camera under all conditions examined in this study with a rise-time range of 6.8 to 16.0 picoseconds. For each zeolite sample the addition of cosolvents decreases the rise time, with a greater decrease for polar solvents than for a nonpolar solvent. The presence of a detectable rise time for excimer emission indicates that pyrene excimer formation is a dynamic process when pyrene is embedded within the cavities of zeolite host materials.

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Ultrafast Dynamics of Pyrene Excimer Formation in Y Zeolites

Cited by 17 publications

References 31 publications

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

[Fe(H₂O)₅(NO)]²⁺, the “Brown‐Ring” Chromophore

Resolution of Ultrafast Pyrene Excimer Emission Rise Times in Zeolites X and Y†

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Ultrafast Dynamics of Pyrene Excimer Formation in Y Zeolites

Cited by 17 publications

References 31 publications

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

The mechanism of excimer formation: an experimental and theoretical study on the pyrene dimer

[Fe(H2O)5(NO)]2+, the “Brown‐Ring” Chromophore

Resolution of Ultrafast Pyrene Excimer Emission Rise Times in Zeolites X and Y†

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Product

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[Fe(H₂O)₅(NO)]²⁺, the “Brown‐Ring” Chromophore