8 research outputs found
Spectrally Selective Leakage of Light from Self-Assembled Supramolecular Nanofiber Waveguides Induced by Surface Plasmon Polaritons
We report surface plasmon polariton
(SPP)-induced spectrally
selective
leakage of light waveguided in supramolecular nanofibers. The nanofibers
are fabricated by self-assembly of tris(phenylisoxazolyl)benzene derivative
molecules, and their diameter ranges from nanometers to hundreds of
nanometers. Nanofibers with heights of more than 200 nm are shown
to function as waveguides for fluorescence excited in one location
by a focused 360 nm laser. The fluorescence can transfer the whole
length of the nanofibers of tens of micrometers and is outcoupled
from the nanofiber ends. The waveguiding phenomenon dramatically changes
when the nanofibers are deposited on SPP-generating substrates. The
substrates in the form of nanohole arrays are fabricated on a gold
film with a pitch of 500 nm, a diameter of 250 nm, and a depth of
40 nm. On the SPP substrates, the nanofiber waveguides exhibit strong
leakage of the guided light. The spectrum of the leaked light is consistent
with the SPP resonance wavelength, and its polarization corresponds
to the TE waveguided mode. We propose mechanisms of the observed phenomena
that include either excitation of the SPPs via the waveguide evanescent
field or direct enhancement of the leakage by the modified density
of states near the plasmonic substrate
Luminescent Mechanochromic 9‑Anthryl Gold(I) Isocyanide Complex with an Emission Maximum at 900 nm after Mechanical Stimulation
Upon
mechanical stimulation, 9-anthryl gold(I) isocyanide complex <b>3</b> exhibited a bathochromic shift of its emission color from
the visible to the infrared (IR) region, which is unprecedented in
its magnitude. Prior to exposure to the mechanical stimulus, the polymorphs <b>3α</b> and <b>3β</b> exhibit emission wavelength
maxima (λ<sub>em,max</sub>) at 448 and 710 nm, respectively.
Upon grinding, the λ<sub>em,max</sub> of <b>3α</b><sub>ground</sub> and <b>3β</b><sub>ground</sub> are
bathochromically shifted to 900 nm, i.e., Δλ<sub>em,max</sub> (<b>3α</b>) = 452 nm or 1.39 eV. Polymorphs <b>3α</b> and <b>3β</b> thus represent the first examples of mechanochromic
luminescent materials with λ<sub>em,max</sub> in the IR region
Luminescent Mechanochromic 9‑Anthryl Gold(I) Isocyanide Complex with an Emission Maximum at 900 nm after Mechanical Stimulation
Upon
mechanical stimulation, 9-anthryl gold(I) isocyanide complex <b>3</b> exhibited a bathochromic shift of its emission color from
the visible to the infrared (IR) region, which is unprecedented in
its magnitude. Prior to exposure to the mechanical stimulus, the polymorphs <b>3α</b> and <b>3β</b> exhibit emission wavelength
maxima (λ<sub>em,max</sub>) at 448 and 710 nm, respectively.
Upon grinding, the λ<sub>em,max</sub> of <b>3α</b><sub>ground</sub> and <b>3β</b><sub>ground</sub> are
bathochromically shifted to 900 nm, i.e., Δλ<sub>em,max</sub> (<b>3α</b>) = 452 nm or 1.39 eV. Polymorphs <b>3α</b> and <b>3β</b> thus represent the first examples of mechanochromic
luminescent materials with λ<sub>em,max</sub> in the IR region
Effective Photosensitized Energy Transfer of Nonanuclear Terbium Clusters Using Methyl Salicylate Derivatives
The photophysical properties of the
novel nonanuclear Tb(III) clusters
Tb-L1 and Tb-L2 involving the ligands methyl 4-methylsalicylate (L1)
and methyl 5-methylsalicylate (L2) are reported. The position of the
methyl group has an effect on their photophysical properties. The
prepared nonanuclear Tb(III) clusters were identified by fast atom
bombardment mass spectrometry and powder X-ray diffraction. Characteristic
photophysical properties, including photoluminescence spectra, emission
lifetimes, and emission quantum yields, were determined. The emission
quantum yield of Tb-L1 (Φ<sub>ππ*</sub> = 31%) was
found to be 13 times larger than that of Tb-L2 (Φ<sub>ππ*</sub> = 2.4%). The photophysical characterization and DFT calculations
reveal the effect of the methyl group on the electronic structure
of methylsalicylate ligand. In this study, the photophysical properties
of the nonanuclear Tb(III) clusters are discussed in relation to the
methyl group on the aromatic ring of the methylsalicylate ligand
Luminescent Mechanochromic 9‑Anthryl Gold(I) Isocyanide Complex with an Emission Maximum at 900 nm after Mechanical Stimulation
Upon
mechanical stimulation, 9-anthryl gold(I) isocyanide complex <b>3</b> exhibited a bathochromic shift of its emission color from
the visible to the infrared (IR) region, which is unprecedented in
its magnitude. Prior to exposure to the mechanical stimulus, the polymorphs <b>3α</b> and <b>3β</b> exhibit emission wavelength
maxima (λ<sub>em,max</sub>) at 448 and 710 nm, respectively.
Upon grinding, the λ<sub>em,max</sub> of <b>3α</b><sub>ground</sub> and <b>3β</b><sub>ground</sub> are
bathochromically shifted to 900 nm, i.e., Δλ<sub>em,max</sub> (<b>3α</b>) = 452 nm or 1.39 eV. Polymorphs <b>3α</b> and <b>3β</b> thus represent the first examples of mechanochromic
luminescent materials with λ<sub>em,max</sub> in the IR region
Fully Conjugated Porphyrin Glass: Collective Light-Harvesting Antenna for Near-Infrared Fluorescence beyond 1 μm
Expanded
π-systems with a narrow highest occupied molecular
orbital–lowest unoccupied molecular orbital band gap encounter
deactivation of excitons due to the “energy gap law”
and undesired aggregation. This dilemma generally thwarts the near-infrared
(NIR) luminescence of organic π-systems. A sophisticated cofacially
stacked π-system is known to involve exponentially tailed disorder,
which displays exceptionally red-shifted fluorescence even as only
a marginal emission component. Enhancement of the tail-state fluorescence
might be advantageous to achieve NIR photoluminescence with an expected
collective light-harvesting antenna effect as follows: (i) efficient
light-harvesting capacity due to intense electronic absorption, (ii)
a long-distance exciton migration into the tail state based on a high
spatial density of the chromophore site, and (iii) substantial transmission
of NIR emission to circumvent the inner filter effect. Suppression
of aggregation-induced quenching of fluorescence could realize collective
light-harvesting antenna for NIR-luminescence materials. This study
discloses an enhanced tail-state NIR fluorescence of a self-standing
porphyrin film at 1138 nm with a moderate quantum efficiency based
on a fully π-conjugated porphyrin that adopts an amorphous form,
called “porphyrin glass”
Development of Ion-Conductive and Vapoluminescent Porous Coordination Polymers Composed of Ruthenium(II) Metalloligand
We
synthesized two new porous
coordination polymers (PCPs) {Ln<sub>7</sub>(OH)<sub>5</sub>[Ru(dcbpy)<sub>3</sub>]<sub>4</sub>·4<i>n</i>H<sub>2</sub>O} (<b>Ln</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub>; Ln = Ce, Nd) composed of the luminescent ruthenium(II) metalloligand
[Ru(4,4′-dcbpy)<sub>3</sub>]<sup>4–</sup> ([4Ru]; 4,4′-dcbpy
= 4,4′-dicarboxy-2,2′-bipyridine) and lanthanide ions
Ln<sup>3+</sup> (Ln = Ce, Nd). These two PCPs <b>Ln</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> are
isomorphous with the previously reported PCP <b>La</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub>, and the
lattice constants (<i>a</i>, <i>c</i>, and unit
cell volume <i>V</i>) changed systematically according to
the lanthanide contraction. All three <b>Ln</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> compounds have OH<sup>–</sup> anion containing porous structures and a large number
of hydrate water molecules within the pores, resulting in moderate
ion conductivities (10<sup>–6</sup>–10<sup>–7</sup> S cm<sup>–1</sup>) at 90% relative humidity (RH) and 298
K. In contrast, the structural transformation of <b>Ln</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> associated
with water-vapor adsorption/desorption strongly depends on the lanthanide
ion; the <b>Ln</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> compounds with larger Ln<sup>3+</sup> ions recover
the original porous structure at lower relative humidities (RH). A
similar trend was observed for the ion conduction activation energy,
suggesting that the bridging Ln<sup>3+</sup> ion plays an important
role in the formation of the ion-conductive pathways. <b>La</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> and <b>Ce</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> exhibit vapochromic luminescence associated
with water vapor adsorption/desorption, arising from the <sup>3</sup>MLCT emission of [4Ru]. This vapochromic behavior is also affected
by the replacement of the Ln<sup>3+</sup> ion; the vapochromic shift
of <b>Ce</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> was observed at RH values (near 100% RH) higher than
that of <b>La</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub>. <sup>3</sup>MLCT emissions of the [4Ru] metalloligand
in <b>Nd</b><sub><b>7</b></sub><b>-Ru</b><sub><b>4</b></sub> were barely observable in the visible region, but
sharp emission bands characteristic of 4f–4f transitions of
the Nd<sup>3+</sup> ion were observed in the near-infrared (NIR) region
(arising from the <sup>1</sup>MLCT transition of [4Ru]), suggesting
the transfer of energy from the [4Ru] <sup>3</sup>MLCT excited state
to the 4f–4f transition state of the Nd<sup>3+</sup> ions
Solid-State and Nanoparticle Synthesis of EuS<sub><i>x</i></sub>Se<sub>1–<i>x</i></sub> Solid Solutions
Europium chalcogenide alloys, EuS<sub><i>x</i></sub>Se<sub>1–<i>x</i></sub>,
have been synthesized both in
the solid-state and as colloidal nanoparticles; the composition, structure,
magnetism, and optical band gaps have been characterized. The goal
was to observe the consequences of selenium concentration on the electronic
structure as evidenced by the optical and magnetic properties and
whether these properties are maintained in the nanomaterials. Both
solid-state and nanoparticle alloys obey Vegard’s law with
a systematic change in cell constant as confirmed by the powder X-ray
diffraction. The bulk materials form homogeneous alloys that exhibit
a linear change in both magnetic and optical properties as a function
of composition. A synthetic method to prepare nanoalloys with a wide
range of S:Se ratio has been developed. The nanoalloys are homogeneous,
and EDS mapping of single nanoparticles indicates relatively uniform
S and Se composition across the nanocrystals. The magnetic properties
of the nanoparticles appear to parallel those in the solid-state.
Although the composition is an effective tool to tune to the optical
band gap in the solid-state alloys with a linear change in <i>E</i><sub>g</sub> with composition, the nanoparticle optical
band gaps appeared to be shifted, which we attribute to the presence
of an amorphous selenium phase. The study of the properties of colloidal
alloys highlights the importance of the mechanism of nanoparticle
formation to control composition and purity