6 research outputs found
Effect of Proton Substitution by Alkali Ions on the Fluorescence Emission of Rhodamine B Cations in the Gas Phase
The
photophysics of chromophores is strongly influenced by their
environment. Solvation, charge state, and adduct formation significantly
affect ground and excited state energetics and dynamics. The present
study reports on fluorescence emission of rhodamine B cations (RhBH<sup>+</sup>) and derivatives in the gas phase. Substitution of the acidic
proton of RhBH<sup>+</sup> by alkali metal cations, M<sup>+</sup>,
ranging from lithium to cesium leads to significant and systematic
blue shifts of the emission. The gas-phase structures and singlet
transition energies of RhBH<sup>+</sup> and RhBM<sup>+</sup>, M =
Li, Na, K, Rb, and Cs, were investigated using HartreeâFock
theory, density functional methods, second-order MøllerâPlesset
perturbation theory, and the second-order approximate coupled-cluster
model CC2. Comparison of experimental and theoretical results highlights
the need for improved quantum chemical methods, while the hypsochromic
shift observed upon substitution appears best explained by the Stark
effect due to the inhomogeneous electric field generated by the alkali
ions
Gas-Phase Photoluminescence Characterization of Stoichiometrically Pure Nonanuclear Lanthanoid Hydroxo Complexes Comprising Europium or Gadolinium
Gas-phase
photoluminescence measurements involving mass-spectrometric techniques
enable determination of the properties of selected molecular systems
with knowledge of their exact composition and unaffected by matrix
effects such as solvent interactions or crystal packing. The resulting
reduced complexity facilitates a comparison with theory. Herein, we
provide a detailed report of the intrinsic luminescence properties
of nonanuclear europiumÂ(III) and gadoliniumÂ(III) 9-hydroxyÂphenalen-1-one
(HPLN) hydroxo complexes. Luminescence spectra of [Eu<sub>9</sub>(PLN)<sub>16</sub>(OH)<sub>10</sub>]<sup>+</sup> ions reveal an europium-centered
emission dominated by a 4-fold split Eu<sup>III</sup> hypersensitive
transition, while photoluminescence lifetime measurements for both
complexes support an efficient europium sensitization via a PLN-centered
triplet-state manifold. The combination of gas-phase measurements
with density functional theory computations and ligand-field theory
is used to discuss the antiprismatic core structure of the complexes
and to shed light on the energy-transfer mechanism. This methodology
is also employed to fit a new set of parameters, which improves the
accuracy of ligand-field computations of Eu<sup>III</sup> electronic
transitions for gas-phase species
Vibronic Coupling Analysis of the Ligand-Centered Phosphorescence of Gas-Phase Gd(III) and Lu(III) 9âOxophenalen-1-one Complexes
The gas-phase laser-induced
photoluminescence of cationic mononuclear
gadolinium and lutetium complexes involving two 9-oxophenalen-1-one
ligands is reported. Performing measurements at a temperature of 83
K enables us to resolve vibronic transitions. Via comparison to FranckâCondon
computations, the main vibrational contributions to the ligand-centered
phosphorescence are determined to involve rocking, wagging, and stretching
of the 9-oxophenalen-1-oneâlanthanoid coordination in the low-energy
range, intraligand bending, and stretching in the medium- to high-energy
range, rocking of the carbonyl and methine groups, and CâH
stretching beyond. Whereas FranckâCondon calculations based
on density-functional harmonic frequency computations reproduce the
main features of the vibrationally resolved emission spectra, the
absolute transition energies as determined by density functional theory
are off by several thousand wavenumbers. This discrepancy is found
to remain at higher computational levels. The relative energy of the
GdÂ(III) and LuÂ(III) emission bands is only reproduced at the coupled-cluster
singles and doubles level and beyond
Characterization of Nonanuclear Europium and Gadolinium Complexes by Gas-Phase Luminescence Spectroscopy
Gas-phase measurements
using mass-spectrometric techniques allow
determination of the luminescence properties of selected molecular
systems with knowledge of their exact composition. Furthermore, isolated
luminophores are unaffected by matrix effects like solvent interactions
or crystal packing. As a result, the system complexity is reduced
relative to the condensed phase and a direct comparison with theory
is facilitated. Herein, we report the intrinsic luminescence properties
of nonanuclear europiumÂ(III) and gadoliniumÂ(III) 9-hydroxyphenalen-1-one
(HPLN)âhydroxo complexes. Luminescence spectra of [Eu<sub>9</sub>(PLN)<sub>16</sub>(OH)<sub>10</sub>]<sup>+</sup> ions reveal an europium-centered
emission dominated by a 4-fold split EuÂ(III) hypersensitive transition.
The corresponding GdÂ(III) complex, [Gd<sub>9</sub>(PLN)<sub>16</sub>(OH)<sub>10</sub>]<sup>+</sup>, shows a broad emission from a ligand
based triplet state with an onset of about 1000 wavenumbers in excess
of the europium emission. As supported by photoluminescence lifetime
measurements for both complexes, we deduce an efficient europium sensitization
via PLN-based triplet states. The luminescence spectra of the complexes
are discussed in terms of a square antiprismatic europium/gadolinium
core structure as suggested by density functional computations
Substitutional Photoluminescence Modulation in Adducts of a Europium Chelate with a Range of Alkali Metal Cations: A Gas-Phase Study
We present gas-phase dispersed photoluminescence
spectra of europiumÂ(III) 9-hydroxyphenalen-1-one (HPLN) complexes
forming adducts with alkali metal ions ([EuÂ(PLN)<sub>3</sub>M]<sup>+</sup> with M = Li, Na, K, Rb, and Cs) confined in a quadrupole
ion trap for study. The mass selected alkali metal cation adducts
display a split hypersensitive <sup>5</sup>D<sub>0</sub> â <sup>7</sup>F<sub>2</sub> Eu<sup>3+</sup> emission band. One of the two
emission components shows a linear dependence on the radius of the
alkali metal cation whereas the other component displays a quadratic
dependence thereon. In addition, the relative intensities of both
components invert in the same order. The experimental results are
interpreted with the support of density functional calculations and
JuddâOfelt theory, yielding also structural information on
the isolated [EuÂ(PLN)<sub>3</sub>M]<sup>+</sup> chromophores
Photoluminescence Spectroscopy of Mass-Selected Electrosprayed Ions Embedded in Cryogenic Rare-Gas Matrixes
An
apparatus is presented which combines nanoelectrospray ionization
for isolation of large molecular ions from solution, mass-to-charge
ratio selection in gas-phase, low-energy-ion-beam deposition into
a (co-condensed) inert gas matrix and UV laser-induced visible-region
photoluminescence (PL) of the matrix isolated ions. Performance is
tested by depositing three different types of lanthanoid diketonate
cations including also a dissociation product species not directly
accessible by chemical synthesis. For these strongly photoluminescent
ions, accumulation of some femto- to picomoles in a neon matrix (over
a time scale of tens of minutes to several hours) is sufficient to
obtain well-resolved dispersed emission spectra. We have ruled out
contributions to these spectra due to charge neutralization or fragmentation
during deposition by also acquiring photoluminescence spectra of the
same ionic species in the gas phase