9 research outputs found
Synthesis and Photophysical Properties of Difluoroboron Complexes of Curcuminoid Derivatives Bearing Different Terminal Aromatic Units and a <i>meso</i>-Aryl Ring
The
synthesis of nine curcuminoids and their difluoroboron complexes
is described, with seven of them containing a <i>meso</i>-phenyl ring. Dynamic <sup>19</sup>F NMR confirmed the fact that
rotation of that <i>meso</i>-aryl fragment is restricted
in the latter systems at room temperature and become allowed at higher
temperature (>45 °C). The molecular structure of a <i>meso</i>-substituted derivative in the solid state showed that
the phenyl
ring lies in a highly twisted plane with respect to the mean curcuminoid
plane. The photophysical properties of the nine compounds were investigated
in solvents of different polarity. <i>Meso</i>-substitution
with a phenyl ring has little influence on fluorescence emission properties
in solution, radiative and nonradiative kinetic constants being similar
for <i>meso</i>- and nonsubstituted compounds, which is
in contrast to the case of BODIPY derivatives. However, introduction
of an electron donor <i>p</i>-methoxy group at the <i>meso</i>-phenyl ring leads to small perturbation of the curcuminoid
π-system fluorescence emission. We also report the influence
of the <i>meso</i>-phenyl group on the emission properties
of the aggregated solids
Synthesis and Photophysical Properties of Difluoroboron Complexes of Curcuminoid Derivatives Bearing Different Terminal Aromatic Units and a <i>meso</i>-Aryl Ring
The
synthesis of nine curcuminoids and their difluoroboron complexes
is described, with seven of them containing a <i>meso</i>-phenyl ring. Dynamic <sup>19</sup>F NMR confirmed the fact that
rotation of that <i>meso</i>-aryl fragment is restricted
in the latter systems at room temperature and become allowed at higher
temperature (>45 °C). The molecular structure of a <i>meso</i>-substituted derivative in the solid state showed that
the phenyl
ring lies in a highly twisted plane with respect to the mean curcuminoid
plane. The photophysical properties of the nine compounds were investigated
in solvents of different polarity. <i>Meso</i>-substitution
with a phenyl ring has little influence on fluorescence emission properties
in solution, radiative and nonradiative kinetic constants being similar
for <i>meso</i>- and nonsubstituted compounds, which is
in contrast to the case of BODIPY derivatives. However, introduction
of an electron donor <i>p</i>-methoxy group at the <i>meso</i>-phenyl ring leads to small perturbation of the curcuminoid
π-system fluorescence emission. We also report the influence
of the <i>meso</i>-phenyl group on the emission properties
of the aggregated solids
C–H···BF<sub>2</sub>O<sub>2</sub> Interactions in Crystals: A Case for Boron Hydrogen Bonding?
Molecules bearing the borondifluoride
unit represent an important class of dyes. We report the intriguing
occurrence of short H···B contacts in the crystal structure
of compounds featuring the BF<sub>2</sub>O<sub>2</sub> fragment. Using
density functional theory-based calculations, we discovered that,
in contrast to what is suggested by the structural observation, the
driving force behind these short H···B contacts is
not a direct H···B interaction but it relies on the
existence of a combination of single, bifurcated, or trifurcated hydrogen
bond paths that are practically isoenergetic within a broad range
of C–H···B interaction orientations. The BF<sub>2</sub>O<sub>2</sub> group as a whole displays a very isotropic hydrogen
bonding ability and, in turn, a strong adaptability to structural
requirements in the solid state
Adsorption and Growth of Bis-pyrene Molecular Layers on Au(111) Studied by STM
The
adsorption and growth of 1,4-di-<i>n</i>-octyloxy-2,5-bis(pyren-1-ylethenyl)benzene
(bis-pyrene) thermo-evaporated onto a Au(111) single crystal surface
has been investigated using low temperature scanning tunneling microscopy
(STM) under ultrahigh vacuum (UHV) conditions. At low coverage, bis-pyrene
molecules arrange into molecular chains, which exclusively grow on
the fcc domains of Au(111) herringbone reconstruction. In these molecular
chains, the individual molecules are connected by a van der Waals
interaction between the alkyl chains of the molecules. As the coverage
is increased the hcp domains of Au(111) herringbone reconstruction
are also decorated by molecular chains. Finally, for coverages above
0.5 ML, four distinct ordered commensurate phases are observed, which
suggests a delicate balance between the intermolecular and the molecule–surface
interactions. A detailed analysis of the STM images suggests that
distinct molecular configurations of the bis-pyrene compound in these
ordered phases are at the origin of their formation
NIR Emission in Borondifluoride Complexes of 2′-Hydroxychalcone Derivatives Containing an Acetonaphthone Ring
We report the synthesis of borondifluoride
complexes of a series of 2′-hydroxychalcone derivatives containing
the hydroxynaphthone ring. TD-DFT calculations confirm the charge
transfer character of the lowest-energy transition band and reveal
large values for the ground-state dipole moment. The fluorescence
emission spectra in the solid state are considerably red-shifted relative
to those in solution, leading to maximum emission wavelengths spanning
from the far red to the NIR. The emission properties are clearly characteristic
of tightly packed chromophores with strong excitonic coupling, as
confirmed by X-ray structure analysis and electronic absorption spectroscopy.
The optical properties of the six dyes <b>1-BF</b><sub><b>2</b></sub>–<b>6-BF</b><sub><b>2</b></sub> are
discussed in terms of interchromophoric interactions in the crystal
and dipole moment values. Dyes <b>3-BF</b><sub><b>2</b></sub> and <b>4-BF</b><sub><b>2</b></sub> emit light
at 690 and 751 nm with 13% and 6.5% efficiencies, respectively, and
as such they represent very appealing materials. Compound <b>6-BF</b><sub><b>2</b></sub> presents an emission maximum wavelength
at 804 nm with a fluorescence quantum yield value of 2%. This class
of solid-state fluorophores may lead to exciting prospects for the
generation of advanced materials
Blue-Shifting Intramolecular Charge Transfer Emission by Nonlocal Effect of Hyperbolic Metamaterials
Metallic
nanostructures permit controlling various photophysical
processes by coupling photons with plasmonic oscillation of electrons
confined in the tailored nanostructures. One example is hyperbolic
metamaterial (HMM) leading to an enhanced spontaneous emission rate
of emitters located nearby. Noting that emission in organic molecules
is from either π<i>–</i>π* or intramolecular
charge-transfer (ICT) states, we address here how HMM modifies ICT
emission spectral features by comparing them with a spectral shift
dependent on the local polarity of the medium. The 7.0 nm blue shift
is observed in ICT emission from 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran
dispersed into a polymer matrix prepared on HMM multilayered structure,
while no spectral shift is observed in π–π* emission
from perylene diimide. In the frame of the Lippert–Mataga formalism,
the blue shift is explained by the HMM nonlocal effects resulting
from 8% decrease in refractive index and 18% reduction in dielectric
permittivity. This phenomenon was also shown in a hemicurcuminoid
borondifluoride dye yielding 15.0 nm blue shift. Such a capability
of spectral shift control in films by HMM structure opens new prospects
for engineering organic light-emitting devices
Influence of Pyrene Grafting on PMMA Nanosecond Laser Ablation at 248 nm
In this work, we investigate the
effects of KrF nanosecond laser
ablation on poly(methyl methacrylate) (PMMA) in combination with pyrene.
Three materials containing PMMA were studied: (1) one doped with pure
pyrene, (2) one doped with methyl 3-(1-pyrenyl)propanoate (so called
alkylpyrene derivative thereafter), and (3) one grafted with pyrene.
This last new material was developed by covalently bonding pyrene
molecules to PMMA side-chains. A comparative study was undertaken
to determine and compare the respective properties of the PMMA dye
containing pyrene during nanosecond laser ablation at 248 nm. Cavities
were etched for each material with up to 20 pulses for fluences between
0.03 and 1.7 J/cm<sup>2</sup> in samples containing 1, 2, and 4 mol
% chromophore. The threshold fluences and the effective absorption
coefficients were obtained. It was observed that effective absorption
coefficients increased and threshold fluences decreased with the chromophore
percentages in each kind of sample. Ablation parameters were not significantly
modified when the dopant was changed from pyrene to the alkylpyrene
derivative. On the other hand, when pyrene molecules were grafted
on the polymer, the threshold fluences decreased, whereas the effective
absorption coefficients became similar at fluences above 0.6 J/cm<sup>2</sup>
Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1‑Hydroxypyridin-2-one Complexes in Aqueous Solution
A series of 10 tetradentate 1-hydroxy-pyridin-2-one
(1,2-HOPO)
ligands and corresponding eight-coordinated photoluminescent Eu(III)
and Sm(III) complexes were prepared. Generally, the ligands differ
by the linear (nLI) aliphatic linker length, from 2 to 8 methylene
units between the bidentate 1,2-HOPO chelator units. The photoluminescent
quantum yields (Φ<sub>tot</sub>) were found to vary with the
linker length, and the same trend was observed for the Eu(III) and
Sm(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φ<sub>tot</sub>xε).
The change in ligand wrapping pattern between 2LI and 5LI complexes
observed by X-ray diffraction (XRD) is further supported by density
functional theory (DFT) calculations. The bimodal Φ<sub>tot</sub> trends of the Eu(III) and Sm(III) complexes are rationalized by
the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length
Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1‑Hydroxypyridin-2-one Complexes in Aqueous Solution
A series of 10 tetradentate 1-hydroxy-pyridin-2-one
(1,2-HOPO)
ligands and corresponding eight-coordinated photoluminescent Eu(III)
and Sm(III) complexes were prepared. Generally, the ligands differ
by the linear (nLI) aliphatic linker length, from 2 to 8 methylene
units between the bidentate 1,2-HOPO chelator units. The photoluminescent
quantum yields (Φ<sub>tot</sub>) were found to vary with the
linker length, and the same trend was observed for the Eu(III) and
Sm(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φ<sub>tot</sub>xε).
The change in ligand wrapping pattern between 2LI and 5LI complexes
observed by X-ray diffraction (XRD) is further supported by density
functional theory (DFT) calculations. The bimodal Φ<sub>tot</sub> trends of the Eu(III) and Sm(III) complexes are rationalized by
the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length