Influence of the Alkali Metal Cation on the Distance of Electron Migration in Zeolite Y:  A Nanosecond Laser Photolysis Study

Keirstead, Amy E.; Schepp, Norman P.; Cozens, Frances L.

doi:10.1021/jp073369k

Cited by 24 publications

(35 citation statements)

References 29 publications

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“…Charge recombination from the latter states could again populate the emitting 1 P state (see µs-ms experiments). 39,40,41 ps-ns dynamics. As it was not possible to estimate decay times longer than 50 ps with sufficient precision using fluorescence up-conversion we used Time Correlated Single Photon Counting (TCSPC) with a time window of 12 ns after excitation.…”

Section: Steady-state Absorption and Luminescence Experimentsmentioning

confidence: 99%

Structural and Photophysical Characterization of Ag Clusters in LTA Zeolites

et al. 2019

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Ag clusters (AgCLs) confined within Na exchanged-LTA zeolites are studied by X-ray absorption, and steadystate and time-resolved photoluminescence spectroscopies in a coordinated effort to elucidate the photophysical properties and link them to the precise cluster structure. The hydrated sodalite cage contains mostly tetrahedral [Ag 4 (H 2 O) 4 ] clusters located at the center of the sodalite cages, whereas upon dehydration octahedral Ag 6 clusters coordinated with the zeolite framework oxygen (O F) [Ag 6 (O F) 14 ] are formed. TD-DFT and ESR reports suggest that both the Ag 4 and Ag 6 clusters have formally a double positive charge of 2+. Time-resolved spectroscopy shows that at room temperature the emission of the hydrated sample decays with 3.4 ns from a state with the same multiplicity as the ground state. Upon dehydration, the entire excited state dynamics speeds up to 1.2 ps. The microsecond-scale lifetimes observed at 77K suggest the occurrence of two main decay processes for the initially populated singlet state: intersystem crossing and charge transfer. We show that intersystem-crossing yields the formation of a long-lived (409 µs) triplet state 3 P from the 1 P state located at lower energy from which luminescence occurs. There is evidence that when electron transfer takes place, it is followed by electron hole recombination or back electron transfer yielding a relaxed singlet excited state. Upon removal of water ligands the electrostatic field of the framework is enhanced which leads to an increase in the rate constant of charge transfer due to stronger electronic coupling between Ag 6 2+ and trap levels. The dependence of luminescence lifetime on the water content indicates a possible way to speed or delay the electron-hole recombination in a controlled way. ASSOCIATED CONTENT Supporting Information. Detailed discussions, structural properties, steady-state spectra, fs fluorescence upconversion traces, TC-SPC fluorescence decay traces, luminescence decay traces. This material is available free of charge via the Internet at http://pubs.acs.org.

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Section: Steady-state Absorption and Luminescence Experimentsmentioning

confidence: 99%

Structural and Photophysical Characterization of Ag Clusters in LTA Zeolites

et al. 2019

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“…[38] Compartmentalization of electrons away from the initial site of PP 3 ionization decreases dramatically the propensity for charge recombination. [39] In contrast, PP 3 C + -electron pair photoinduced in solution exhibits a short lifetime (on the order of microseconds), because fast charge recombination occurs in solution. The intrinsic stability of PP 3 À ] was reported to be several hours at 0 8C.…”

Section: Wwwchemphyschemorgmentioning

confidence: 99%

Effects of Spatial Constraints and Brønsted Acid Site Locations on para‐Terphenyl Ionization and Charge Transfer in Zeolites

et al. 2011

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The locations of Brønsted acid sites (BAS) in the channels of medium-pore zeolites have a significant effect on the spontaneous ionization of para-terphenyl (PP(3)) insofar as spatial constraints determine the stability of transition states and charge-transfer complexes relevant to charge separation. The ionization rates and ionization yield values demonstrate that a strong synergy exists between the H(+) polarization energy and spatial constraints imposed by the channel topology. Spectroscopic and modeling results show that PP(3) incorporation, charge separation, charge transfer and charge recombination differ dramatically among zeolites with respect to channel structure (H-FER, H-MFI, H-MOR) and BAS density in the channel. Compartmentalization of ejected electrons away from the initial site of ionization decreases dramatically the propensity for charge recombination. The main mode of PP(3)(.+) decay is hole transfer to form AlO(4)H(.+) ⋅⋅⋅PP(3) charge-transfer complexes characterized by intense absorption in the visible range. According to the nonadiabatic electron-transfer theory, the small reorganization energy in constrained channels explains the slow hole-transfer rate.

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“…Among the large variety of porous supports, the most studied ones are those formed by the interaction of a guest molecule with silica-based materials like zeolites, MCM-41, SBA-15, and mesoporous silica nanoparticles. These constituents provide cavities and channels which allow to tune both the spectroscopy and dynamics of trapped molecules by affecting processes like proton-transfer [2,3,4], electron-transfer [5,6,7], and energy-transfer [8,9,10]. The variety of photophysical and photochemical events showed by these composites could be used to develop smart devices such as drug nanocarriers, nanosensors, nanoOLEDs, nanolasers, energy storage nanospace, and nanophotocatalysts [1].…”

Section: Introductionmentioning

confidence: 99%

Confinement Effect of Micro- and Mesoporous Materials on the Spectroscopy and Dynamics of a Stilbene Derivative Dye

Nunzio

Perenlei

Douhal

2019

IJMS

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Micro- and mesoporous silica-based materials are a class of porous supports that can encapsulate different guest molecules. The formation of these hybrid complexes can be associated with significant alteration of the physico-chemical properties of the guests. Here, we report on a photodynamical study of a push–pull molecule, trans-4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), entrapped within faujasite-type zeolites (HY, NaX, and NaY) and MCM-41 in dichloromethane suspensions. The complex formation gives rise to caged monomers and H- and J-aggregates. Steady-state experiments show that the nanoconfinement provokes net blue shifts of both the absorption and emission spectra, which arise from preferential formation of H-aggregates concomitant with a distortion and/or protonation of the DCM structure. The photodynamics of the hybrid complexes are investigated by nano- to picosecond time-resolved emission experiments. The obtained fluorescence lifetimes are 65–99 ps and 350–400 ps for H- and J-aggregates, respectively, while those of monomers are 2.46–3.87 ns. Evidences for the presence of a charge-transfer (CT) process in trapped DCM molecules (monomers and/or aggregates) are observed. The obtained results are of interest in the interpretation of electron-transfer processes, twisting motions of analogues push–pull systems in confined media and understanding photocatalytic mechanisms using this type of host materials.

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Influence of the Alkali Metal Cation on the Distance of Electron Migration in Zeolite Y: A Nanosecond Laser Photolysis Study

Cited by 24 publications

References 29 publications

Structural and Photophysical Characterization of Ag Clusters in LTA Zeolites

Structural and Photophysical Characterization of Ag Clusters in LTA Zeolites

Effects of Spatial Constraints and Brønsted Acid Site Locations on para‐Terphenyl Ionization and Charge Transfer in Zeolites

Confinement Effect of Micro- and Mesoporous Materials on the Spectroscopy and Dynamics of a Stilbene Derivative Dye

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