8 research outputs found
Dynamics of the Formation of a Charge Transfer State in 1,2-Bis(9-anthryl)acetylene in Polar Solvents: Symmetry Reduction with the Participation of an Intramolecular Torsional Coordinate
We
have studied 1,2-bisÂ(9-anthryl)Âacetylene as a model compound
for the characterization of the process of solvent-mediated symmetry
reduction in an excited state. Thanks to the acetylenic bridge that
joins the two anthracenic moieties, this system maintains minimal
steric hindrance between the end chromophores in comparison with the
classic 9,9â˛-bianthryl model compound. The acetylenic bridge
also allows for significant electronic coupling across the molecule,
which permits a redistribution of electron density after light absorption.
Femtosecond resolved fluorescence measurements were used to determine
the spectral evolution in acetonitrile and cyclohexane solutions.
We observed that, for 1,2-bisÂ(9-anthryl)Âacetylene, the formation of
a charge transfer state occurs in a clear bimodal fashion with well
separated time scales. Specifically, the evolution of the emission
spectrum involves a first solvent-response mediated subpicosecond
stage where the fluorescence changes from that typical of nonpolar
solvents (locally excited) to an intermediate, partial charge transfer
state. The second stage of the evolution into a full charge transfer
state occurs with a much longer time constant of 37.3 ps. Since in
this system the steric hindrance is minimized, this molecule can undergo
much larger amplitude motions for the torsion between the two anthracenic
moieties associated with the charge redistribution in comparison with
the typical model compound 9,9â˛-bianthryl. Clearly, the larger
range of motions of 1,2-bisÂ(9-anthryl)Âacetylene gives the opportunity
to study the electron transfer process with a good separation of the
time scales for the formation of a partial charge transfer state,
determined by the speed of solvent response, and the intramolecular
changes associated with the formation of the fully equilibrated charge
transfer state
Nitrated Fluorophore Formation upon Two-Photon Excitation of an Azide with Extended Conjugation
The transformation of an aromatic
azide into a highly fluorescent
species through a nonlinear optical process was studied. The azide
system was designed to undergo N<sub>2</sub> release and nitrene to
nitro conversion upon two-photon electronic excitation. The formation
of the nitro form of the compound through reactions with O<sub>2</sub> and its high radiative quantum yield implies that the azide can
be used as a biphotonic activatable fluorogen. The electronic state
in which the azide to nitrene transformation takes place can be accessed
nonlinearly with near-infrared light which allows for photoactivation
with commonly available lasers. Furthermore, the system was built
with a sulfonate functionality which allows for the molecule to be
adsorbed at surfaces like that of cadmium sulfide nanocrystals which
further improves the nonlinear optical absorption properties in the
composite, through an energy transfer mechanism. The yield of the
process as a function of the excitation photon energy together with
computational studies indicate that the N<sub>2</sub> release in this
azide is due to a reactive channel in the second singlet excited state
of the molecule. This feature implies that the system is intrinsically
photostable for excitation below and above a certain wavelength and
that the system can be phototriggered selectively by the nonlinear
optical process
OrganicâInorganic Hybrid Glasses of Atomically Precise Nanoclusters
Organicâinorganic atomically precise nanoclusters
provide
indispensable building blocks for establishing structureâproperty
links in hybrid condensed matter. However, robust glasses of ligand-protected
nanocluster solids have yet to be demonstrated. Herein, we show [Cu4I4(PR3)4] cubane nanoclusters
coordinated by phosphine ligands (PR3) form robust melt-quenched
glasses in air with reversible crystalâliquidâglass
transitions. Protective phosphine ligands critically influence the
glass formation mechanism, modulating the glassesâ physical
properties. A hybrid glass utilizing ethyldiphenylphosphine-based
nanoclusters, [Cu4I4(PPh2Et)4], exhibits superb optical properties, including >90% transmission
in both visible and near-infrared wavelengths, negligible self-absorption,
near-unity quantum yield, and high light yield. Experimental and theoretical
analyses demonstrate the structural integrity of the [Cu4I4(PPh2Et)4] nanocluster, i.e.,
iodine-bridged tetranuclear cubane, has been fully preserved in the
glass state. The strong internanocluster CHâĎ interactions
found in the [Cu4I4(PPh2Et)4] glass and subsequently reduced structural vibration account for
its enhanced luminescence properties. Moreover, this highly transparent
glass enables performant X-ray imaging and low-loss waveguiding in
fibers drawn above the glass transition. The discovery of ânanocluster
glassâ opens avenues for unraveling glass formation mechanisms
and designing novel luminescent glasses of well-defined building blocks
for advanced photonics
OrganicâInorganic Hybrid Glasses of Atomically Precise Nanoclusters
Organicâinorganic atomically precise nanoclusters
provide
indispensable building blocks for establishing structureâproperty
links in hybrid condensed matter. However, robust glasses of ligand-protected
nanocluster solids have yet to be demonstrated. Herein, we show [Cu4I4(PR3)4] cubane nanoclusters
coordinated by phosphine ligands (PR3) form robust melt-quenched
glasses in air with reversible crystalâliquidâglass
transitions. Protective phosphine ligands critically influence the
glass formation mechanism, modulating the glassesâ physical
properties. A hybrid glass utilizing ethyldiphenylphosphine-based
nanoclusters, [Cu4I4(PPh2Et)4], exhibits superb optical properties, including >90% transmission
in both visible and near-infrared wavelengths, negligible self-absorption,
near-unity quantum yield, and high light yield. Experimental and theoretical
analyses demonstrate the structural integrity of the [Cu4I4(PPh2Et)4] nanocluster, i.e.,
iodine-bridged tetranuclear cubane, has been fully preserved in the
glass state. The strong internanocluster CHâĎ interactions
found in the [Cu4I4(PPh2Et)4] glass and subsequently reduced structural vibration account for
its enhanced luminescence properties. Moreover, this highly transparent
glass enables performant X-ray imaging and low-loss waveguiding in
fibers drawn above the glass transition. The discovery of ânanocluster
glassâ opens avenues for unraveling glass formation mechanisms
and designing novel luminescent glasses of well-defined building blocks
for advanced photonics
Quantum Tunneling Effect in CsPbBr<sub>3</sub> Multiple Quantum Wells
Two-dimensional
(2D) lead halide perovskites (LHPs) have garnered
incredible attention thanks to their exciting optoelectronic properties
and intrinsic strong quantum confinement effect. Herein, we carefully
investigate and decipher the charge carrier dynamics at the interface
between CsPbBr3 multiple quantum wells (MQWs) as the photoactive
layer and TiO2 and Spiro-OMeTAD as electron and hole transporting
materials, respectively. The fabricated MQWs comprise three monolayers
of CsPbBr3 separated by 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline
(BCP) as barriers. By varying the BCP thickness, we show that charge
carrier extraction from MQWs to the corresponding extracting layer
occurs through a quantum tunneling effect, as elaborated by steady-state
and time-resolved photoluminescence measurements and further verified
by femtosecond transient absorption experiments. Ultimately, we have
investigated the impact of the barrier-thickness-dependent quantum
tunneling effect on the photoelectric behavior of the synthesized
QW photodetector devices. Our findings shed light on one of the most
promising approaches for efficient carrier extraction in quantum-confined
systems
OrganicâInorganic Hybrid Glasses of Atomically Precise Nanoclusters
Organicâinorganic atomically precise nanoclusters
provide
indispensable building blocks for establishing structureâproperty
links in hybrid condensed matter. However, robust glasses of ligand-protected
nanocluster solids have yet to be demonstrated. Herein, we show [Cu4I4(PR3)4] cubane nanoclusters
coordinated by phosphine ligands (PR3) form robust melt-quenched
glasses in air with reversible crystalâliquidâglass
transitions. Protective phosphine ligands critically influence the
glass formation mechanism, modulating the glassesâ physical
properties. A hybrid glass utilizing ethyldiphenylphosphine-based
nanoclusters, [Cu4I4(PPh2Et)4], exhibits superb optical properties, including >90% transmission
in both visible and near-infrared wavelengths, negligible self-absorption,
near-unity quantum yield, and high light yield. Experimental and theoretical
analyses demonstrate the structural integrity of the [Cu4I4(PPh2Et)4] nanocluster, i.e.,
iodine-bridged tetranuclear cubane, has been fully preserved in the
glass state. The strong internanocluster CHâĎ interactions
found in the [Cu4I4(PPh2Et)4] glass and subsequently reduced structural vibration account for
its enhanced luminescence properties. Moreover, this highly transparent
glass enables performant X-ray imaging and low-loss waveguiding in
fibers drawn above the glass transition. The discovery of ânanocluster
glassâ opens avenues for unraveling glass formation mechanisms
and designing novel luminescent glasses of well-defined building blocks
for advanced photonics
OrganicâInorganic Hybrid Glasses of Atomically Precise Nanoclusters
Organicâinorganic atomically precise nanoclusters
provide
indispensable building blocks for establishing structureâproperty
links in hybrid condensed matter. However, robust glasses of ligand-protected
nanocluster solids have yet to be demonstrated. Herein, we show [Cu4I4(PR3)4] cubane nanoclusters
coordinated by phosphine ligands (PR3) form robust melt-quenched
glasses in air with reversible crystalâliquidâglass
transitions. Protective phosphine ligands critically influence the
glass formation mechanism, modulating the glassesâ physical
properties. A hybrid glass utilizing ethyldiphenylphosphine-based
nanoclusters, [Cu4I4(PPh2Et)4], exhibits superb optical properties, including >90% transmission
in both visible and near-infrared wavelengths, negligible self-absorption,
near-unity quantum yield, and high light yield. Experimental and theoretical
analyses demonstrate the structural integrity of the [Cu4I4(PPh2Et)4] nanocluster, i.e.,
iodine-bridged tetranuclear cubane, has been fully preserved in the
glass state. The strong internanocluster CHâĎ interactions
found in the [Cu4I4(PPh2Et)4] glass and subsequently reduced structural vibration account for
its enhanced luminescence properties. Moreover, this highly transparent
glass enables performant X-ray imaging and low-loss waveguiding in
fibers drawn above the glass transition. The discovery of ânanocluster
glassâ opens avenues for unraveling glass formation mechanisms
and designing novel luminescent glasses of well-defined building blocks
for advanced photonics
OrganicâInorganic Hybrid Glasses of Atomically Precise Nanoclusters
Organicâinorganic atomically precise nanoclusters
provide
indispensable building blocks for establishing structureâproperty
links in hybrid condensed matter. However, robust glasses of ligand-protected
nanocluster solids have yet to be demonstrated. Herein, we show [Cu4I4(PR3)4] cubane nanoclusters
coordinated by phosphine ligands (PR3) form robust melt-quenched
glasses in air with reversible crystalâliquidâglass
transitions. Protective phosphine ligands critically influence the
glass formation mechanism, modulating the glassesâ physical
properties. A hybrid glass utilizing ethyldiphenylphosphine-based
nanoclusters, [Cu4I4(PPh2Et)4], exhibits superb optical properties, including >90% transmission
in both visible and near-infrared wavelengths, negligible self-absorption,
near-unity quantum yield, and high light yield. Experimental and theoretical
analyses demonstrate the structural integrity of the [Cu4I4(PPh2Et)4] nanocluster, i.e.,
iodine-bridged tetranuclear cubane, has been fully preserved in the
glass state. The strong internanocluster CHâĎ interactions
found in the [Cu4I4(PPh2Et)4] glass and subsequently reduced structural vibration account for
its enhanced luminescence properties. Moreover, this highly transparent
glass enables performant X-ray imaging and low-loss waveguiding in
fibers drawn above the glass transition. The discovery of ânanocluster
glassâ opens avenues for unraveling glass formation mechanisms
and designing novel luminescent glasses of well-defined building blocks
for advanced photonics