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_em,max) at 448 and 710 nm, respectively. Upon grinding, the λ_em,max of <b>3α</b>_ground and <b>3β</b>_ground are bathochromically shifted to 900 nm, i.e., Δλ_em,max (<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_em,max 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_em,max) at 448 and 710 nm, respectively. Upon grinding, the λ_em,max of <b>3α</b>_ground and <b>3β</b>_ground are bathochromically shifted to 900 nm, i.e., Δλ_em,max (<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_em,max 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_ππ* = 31%) was found to be 13 times larger than that of Tb-L2 (Φ_ππ* = 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_em,max) at 448 and 710 nm, respectively. Upon grinding, the λ_em,max of <b>3α</b>_ground and <b>3β</b>_ground are bathochromically shifted to 900 nm, i.e., Δλ_em,max (<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_em,max 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) {Ln₇(OH)₅[Ru­(dcbpy)₃]₄·4<i>n</i>H₂O} (<b>Ln</b>_<b>7</b><b>-Ru</b>_<b>4</b>; Ln = Ce, Nd) composed of the luminescent ruthenium­(II) metalloligand [Ru­(4,4′-dcbpy)₃]^4– ([4Ru]; 4,4′-dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) and lanthanide ions Ln³⁺ (Ln = Ce, Nd). These two PCPs <b>Ln</b>_<b>7</b><b>-Ru</b>_<b>4</b> are isomorphous with the previously reported PCP <b>La</b>_<b>7</b><b>-Ru</b>_<b>4</b>, 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>_<b>7</b><b>-Ru</b>_<b>4</b> compounds have OH^– anion containing porous structures and a large number of hydrate water molecules within the pores, resulting in moderate ion conductivities (10^–6–10^–7 S cm^–1) at 90% relative humidity (RH) and 298 K. In contrast, the structural transformation of <b>Ln</b>_<b>7</b><b>-Ru</b>_<b>4</b> associated with water-vapor adsorption/desorption strongly depends on the lanthanide ion; the <b>Ln</b>_<b>7</b><b>-Ru</b>_<b>4</b> compounds with larger Ln³⁺ 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 Ln³⁺ ion plays an important role in the formation of the ion-conductive pathways. <b>La</b>_<b>7</b><b>-Ru</b>_<b>4</b> and <b>Ce</b>_<b>7</b><b>-Ru</b>_<b>4</b> exhibit vapochromic luminescence associated with water vapor adsorption/desorption, arising from the ³MLCT emission of [4Ru]. This vapochromic behavior is also affected by the replacement of the Ln³⁺ ion; the vapochromic shift of <b>Ce</b>_<b>7</b><b>-Ru</b>_<b>4</b> was observed at RH values (near 100% RH) higher than that of <b>La</b>_<b>7</b><b>-Ru</b>_<b>4</b>. ³MLCT emissions of the [4Ru] metalloligand in <b>Nd</b>_<b>7</b><b>-Ru</b>_<b>4</b> were barely observable in the visible region, but sharp emission bands characteristic of 4f–4f transitions of the Nd³⁺ ion were observed in the near-infrared (NIR) region (arising from the ¹MLCT transition of [4Ru]), suggesting the transfer of energy from the [4Ru] ³MLCT excited state to the 4f–4f transition state of the Nd³⁺ ions

Solid-State and Nanoparticle Synthesis of EuS_<i>x</i>Se_1–<i>x</i> Solid Solutions

Europium chalcogenide alloys, EuS_<i>x</i>Se_1–<i>x</i>, 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>_g 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