Investigation of Electronic Structures of Triplet States Using Step-Scan Time-Resolved Fourier-Transform Near-Infrared Spectroscopy.

Triplet transitions of light-emitting materials, including rose bengal, tris(2-phenylpyridine)iridium(III) [Ir(ppy)3], tris(1-phenylisoquinoline)iridium(III) [Ir(piq)3], and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic), were studied using step-scan time-resolved Fourier-transform near-infrared spectroscopy. The samples were excited to their singlet excited states by a 355 nm laser and then underwent efficient conversions/crossings to their triplet manifolds. For rose bengal, a transient absorption band appeared at 9400 cm-1, attributed to the T3 ← T1 transition based on the corresponding time evolution and the theoretical calculations. For Ir(ppy)3, Ir(piq)3, and FIrpic, the most intense bands were observed at 7700, 7500, and 7500 cm-1 and assigned to T7 ← T1, T6 ← T1, and T6 ← T1 transitions, respectively. For Ir(ppy)3, the most intense band involved transitions between different triplet metal-to-ligand charge transfer (3MLCT) states, while for Ir(piq)3 and FIrpic, they involved a metal center to 3MLCT transition. These T1 states were assigned to 3MLCT.

Experimental Revelation of Surface and Bulk Lattices in Faceted Cu2 O Crystals.

Semiconductor crystals have generally shown facet-dependent electrical, photocatalytic, and optical properties. These phenomena have been proposed to result from the presence of a surface layer with bond-level deviations. To provide experimental evidence of this structural feature, synchrotron X-ray sources are used to obtain X-ray diffraction (XRD) patterns of polyhedral cuprous oxide crystals. Cu2 O rhombic dodecahedra display two distinct cell constants from peak splitting. Peak disappearance during slow Cu2 O reduction to Cu with ammonia borane differentiates bulk and surface layer lattices. Cubes and octahedra also show two peak components, while diffraction peaks of cuboctahedra are comprised of three components. Temperature-varying lattice changes in the bulk and surface regions also show shape dependence. From transmission electron microscopy (TEM) images, slight plane spacing deviations in surface and inner crystal regions are measured. Image processing provides visualization of the surface layer with depths of about 1.5-4 nm giving dashed lattice points instead of dots from atomic position deviations. Close TEM examination reveals considerable variation in lattice spot size and shape for different particle morphologies, explaining why facet-dependent properties are emerged. Raman spectrum reflects the large bulk and surface lattice difference in rhombic dodecahedra. Surface lattice difference can change the particle bandgap.

In situ and real-time vibrational spectroscopic characterizations of the photodegradation of nitrite in the presence of methanediol.

Nitrite (NO2-) is one of the common salts in aqueous aerosols, and its photolytic products, nitric oxide (NO) and hydroxyl radical (OH), have potential for use in the oxidation of organic matter, such as dissolved formaldehyde, methanediol (CH2(OH)2), which is regarded as the precursor of atmospheric formic acid. In this work, the simulation of UVA irradiation in an aqueous mixture of NaNO2/CH2(OH)2 was carried out via continuous exposure with a 365 nm LED lamp, and the reaction evolutions were probed by in situ and real-time infrared and Raman spectroscopy, which provided multiplexity in the identification of the relevant species and the corresponding reaction evolution. Although performing infrared absorption measurements in aqueous solution seemed impracticable due to the strong interference of water, the multiplexity of the vibrational bands of parents and products in the non-interfered infrared regimes and the conjunction with Raman spectroscopy still make it possible to perform in situ and real-time characterization of the photolytic reaction in the aqueous phase, supplementary to chromatographic approaches. During the 365 nm irradiation, NO2- and CH2(OH)2 gradually decreased, concomitant with the formation of nitrous oxide (N2O) and formate (HCOO-) in the early period and carbonate (CO32-) in the late period, as revealed by the vibrational spectra. The losses or the gains of the aforementioned species increased with increases in the concentration of CH2(OH)2 and the irradiation flux of the 365 nm UV light. The ionic product HCOO- was also confirmed by ion chromatography, but oxalate (C2O42-) was absent in the vibrational spectra and ion chromatogram. The reaction mechanism is reasonably proposed on the basis of the evolutions of the aforementioned species and the predicted thermodynamic favorableness.

The twisting elevator mechanism of glutamate transporters reveals the structural basis for the dual transport-channel functions.

Glutamate transporters facilitate the removal of this excitatory neurotransmitter from the synapse. Increasing evidence indicates that this process is linked to intrinsic chloride channel activity that is thermodynamically uncoupled from substrate transport. A recent cryo-EM structure of GltPh - an archaeal homolog of the glutamate transporters - in an open channel state has shed light on the structural basis for channel opening formed at the interface of two domains within the transporter which is gated by two clusters of hydrophobic residues. These transporters cycle through several conformational states during the transport process, including the chloride conducting state, which appears to be stabilised by protein-membrane interactions and membrane deformation. Several point mutations that perturb the chloride conductance can have detrimental effects and are linked to the pathogenesis of the neurological disorder, episodic ataxia type 6.

Glutamate transporters have a chloride channel with two hydrophobic gates.

Glutamate is the most abundant excitatory neurotransmitter in the central nervous system, and its precise control is vital to maintain normal brain function and to prevent excitotoxicity1. The removal of extracellular glutamate is achieved by plasma-membrane-bound transporters, which couple glutamate transport to sodium, potassium and pH gradients using an elevator mechanism2-5. Glutamate transporters also conduct chloride ions by means of a channel-like process that is thermodynamically uncoupled from transport6-8. However, the molecular mechanisms that enable these dual-function transporters to carry out two seemingly contradictory roles are unknown. Here we report the cryo-electron microscopy structure of a glutamate transporter homologue in an open-channel state, which reveals an aqueous cavity that is formed during the glutamate transport cycle. The functional properties of this cavity, combined with molecular dynamics simulations, reveal it to be an aqueous-accessible chloride permeation pathway that is gated by two hydrophobic regions and is conserved across mammalian and archaeal glutamate transporters. Our findings provide insight into the mechanism by which glutamate transporters support their dual function, and add information that will assist in mapping the complete transport cycle shared by the solute carrier 1A transporter family.

Study of Electronic and Vibrational Structures of Reduced, Neutral, and Oxidized Ni3(dpa)4X2 Using Density Functional Theory and Raman Spectroscopy.

The electronic and vibrational structures of trinickel metal string complexes [Ni3(dpa)4X2]1-,0,1+ (X = Cl, NCS) were investigated using both theoretical calculations and spectroscopic methods. We used the density functional theory (DFT) method B3LYP*-D3, including less exact exchange energy and the van der Waals interaction of metal ions, to obtain the geometries and vibrational structures, which were found to be in excellent agreement with the experimental data. The ground state of Ni3(dpa)4X2 is an antiferromagnetic (AF) singlet state, and the next state is a quintet state, which was detected using temperature-dependent Raman spectroscopy under a magnetic field. The vibrational structure of the quintet state is nearly identical to that of the AF state, according to the measured Raman spectra, except that the stretching of Ni-Cl is blue-shifted from 282.5 cm-1 in the AF state to 283.8 cm-1 in the quintet state. Two oxidized Ni3 complexes were found to have [Ni3]7+ cores, the doublet [Ni3(dpa)4]3+ without axial ligands and the quartet [Ni3(dpa)4X2]+. Complex [Ni3(dpa)4X2]-, which was produced from a reduction reaction by gold nanoparticles at room temperature, consists of a quartet state as the ground state and a doublet state lying nearby.

Craniofacial, dental arch morphology, and characteristics in preschool children with mild obstructive sleep apnea.

BACKGROUND/PURPOSE: Pediatric obstructive sleep apnea (OSA) might be a serious cause of neurocognitive deficits, behavioral changes, and craniofacial disharmony in children at very young age with mild type of OSA. This study aims to examine the effect of mild OSA on craniofacial morphology as well as dental arch morphology and characteristics in preschool children. MATERIALS AND METHODS: The test group comprised 16 preschool children (11 boys, 5 girls; mean age: 5.14 years old; mean AHI: 2.02) with confirmed polysomnographic diagnosis of mild OSA. Ten control subjects also underwent polysomnography (5 boys, 5 girls; mean age: 5.18 years old; median AHI: 0.43). Lateral cephalometric radiographs and dental arch impressions were obtained and measured. A survey on characteristics and quality of life (OSA-18) was filled out by study participants' caregivers. RESULTS: For craniofacial morphology, a significant increase in ANB angle, a decrease in SNB angle, and larger overjet size were seen in the group with mild OSA, compared with the control group. More frequent sleep disturbances and mood swing were also found in children with mild OSA, based on the OSA-18 assessment. CONCLUSION: Preschool children with mild OSA present the following: skeletal Class II pattern with a more retrognathic mandible, increased overjet size, and more pronounced symptoms in the domains of sleep and emotion. Dental arch constriction is not a typical feature in our sample of Asian preschool children with mild OSA.

Palladium-catalyzed α-arylation of indolin-3-ones.

A method for the catalytic α-arylation of indolin-3-ones was developed. The catalytic system comprising Pd(dba)2 and PAd3 was found to be optimal for the transformation. The protocol features broad functional group compatibility in that a range of arylated indoxyl derivatives bearing a fully substituted carbon center was synthesized with high efficiency. A preliminary bioassay study revealed that the selected indole-substituted indolin-3-ones exhibit favorable cytotoxic activities against HCT-116 cancer cell line.

Amino Acid Transporters and Exchangers from the SLC1A Family: Structure, Mechanism and Roles in Physiology and Cancer.

The Solute Carrier 1A (SLC1A) family includes two major mammalian transport systems-the alanine serine cysteine transporters (ASCT1-2) and the human glutamate transporters otherwise known as the excitatory amino acid transporters (EAAT1-5). The EAATs play a critical role in maintaining low synaptic concentrations of the major excitatory neurotransmitter glutamate, and hence they have been widely researched over a number of years. More recently, the neutral amino acid exchanger, ASCT2 has garnered attention for its important role in cancer biology and potential as a molecular target for cancer therapy. The nature of this role is still being explored, and several classes of ASCT2 inhibitors have been developed. However none have reached sufficient potency or selectivity for clinical use. Despite their distinct functions in biology, the members of the SLC1A family display structural and functional similarity. Since 2004, available structures of the archaeal homologues GltPh and GltTk have elucidated mechanisms of transport and inhibition common to the family. The recent determination of EAAT1 and ASCT2 structures may be of assistance in future efforts to design efficacious ASCT2 inhibitors. This review will focus on ASCT2, the present state of knowledge on its roles in tumour biology, and how structural biology is being used to progress the development of inhibitors.

Investigation of the cis-trans structures and isomerization of oligoprolines by using Raman spectroscopy and density functional theory calculations: solute-solvent interactions and effects of terminal positively charged amino acid residues.

Using low-wavenumber Raman spectroscopy in combination with theoretical calculations via solid-state density functional theory (DFT)-D3, we studied the vibrational structures and interaction with solvent of poly-l-proline and the oligoproline P12 series. The P12 series includes P12, the positively charged amino acid residue (arginine and lysine) N-terminus proline oligomers RP11 and KP11, and the C-terminus P11R and P11K. We assigned the spring-type phonon mode to 74-76 cm-1 bands for the PPI and PPII conformers and the carbonyl group ring-opening mode 122 cm-1 in the PPI conformer of poly-l-proline. Amide I and II were assigned based on the results of mode analysis for O, N, and C atom displacements. The broad band feature of the H-bond transverse mode in the Raman spectra indicates that the positively charged proline oligomers PPII form H-bonds with water in the solid phase, whereas P12 is relatively more hydrophobic. In propanol, the PPI conformer of the P12 series forms less H-bond network with the solvent. The PPII conformer exhibits a distinct Raman band at 310 cm-1, whereas the PPI has bands at 365, 660, and 960 cm-1 with reasonable intensity that can be used to quantitatively determine these two conformational forms. The 365 cm-1 mode comprising the motion of a C[double bond, length as m-dash]O group turning to the helix axis was used to monitor the isomerization reaction PPI ↔ PPII. In pure propanol, RP11 and KP11 were found to have mostly PPI present, but P11R and P11K preferred PPII. After adding 20% water, the PPI in P11R and P11K was completely converted to PPII, whereas a small fraction of PPI remained in RP11 and KP11. The substituted positively charged amino acid affected the balance of the PPI/PPII population ratio.

Influence of Lipid Compositions in the Events of Retinal Schiff Base of Bacteriorhodopsin Embedded in Covalently Circularized Nanodiscs: Thermal Isomerization, Photoisomerization, and Deprotonation.

Covalently circularized nanodiscs using circular membrane scaffold protein (MSP) serve as a suitable membrane mimetic for transmembrane proteins by providing stability and tunability in lipid compositions, providing controllable biological environments for targeted proteins. In this work, monomeric bacteriorhodopsin (mbR) was embedded in lipid nanodiscs of different lipid compositions using negatively charged lipid dioleoyl phosphatidylglycerol (DOPG) and the zwitterion lipid dioleoyl phosphatidylcholine (DOPC), and the events associated with the retinal Schiff base, including the thermal isomerization during the dark adaptation, photoisomerization, and deprotonation, were investigated. The retinal thermal isomerization from all-trans, 15-anti to the 13-cis, 15-syn configuration during the dark adaptation was accelerated in the DOPG bilayer, whereas the processes in the DOPC bilayer and in Triton X-100 micelles were similar. This observation indicated that the negatively charged lipid reduced the barrier for retinal thermal isomerization at C13═C14-C15═N in the ground electronic state. Furthermore, the broader absorption contour of mbR in the DOPC nanodisc probably indicated various retinal isomers in the light-adapted state, consistent with the observed nontwo-state dark adaptation kinetics. Moreover, the kinetics of the photoisomerization of the retinal was slightly decelerated upon increasing the content of DOPC. However, the cascading deprotonation of the protonated Schiff base is not dependent on the types of the surrounding lipids in the nanodiscs. In summary, our research deepens the understanding of the coupling between lipid membrane and the photochemistry of bR retinal Schiff base. Combined with the results of our previous works (Lee, T.-Y.; Yeh, V.; Chuang, J.; Chan, J. C. C.; Chu, L.-K.; Yu, T.-Y. Biophys. J. 2015, 109, 1899-1906; Kao, Y.-M.; Cheng, C.-H.; Syue, M.-L.; Huang, H.-Y.; Chen, I-C.; Yu, T.-Y.; Chu, L.-K. J. Phys. Chem. B 2019, 123, 2032-2039), these outcomes extend our understanding of the control of photochemistry and biophysical events for other photosynthetic proteins via altering the lipid environments.

Facet-Dependent Reduction Reaction of Diruthenium Metal-String Complexes by Face-to-Face Linked Gold Nanocrystals.

The facet-dependent redox reactions of diruthenium metal-string complexes by gold nanoparticles (AuNPs) are explored by using the surface-enhanced Raman scattering (SERS) technique. Gold nano-rhombic dodecahedrons (AuRDs), gold nanocubes (AuNCs), and gold octahedrons (AuOhs) with exclusive facets {110}, {100}, and {111}, respectively, were synthesized. These AuNPs linked face-to-face by metal-string complexes Ru2M(dpa)4Cl2 (dpa = dipyridyl amino, M = Ni, Cu) with chloride axial ligands serve as both SERS substrates and reducing agents in the reactions. We employ the diruthenium core in these complexes with multiple redox states to study the reduction ability of varied AuNP facets upon plasmonic excitation. In Ru2Ni(dpa)4Cl2, the Ru-Ru stretching mode νRu-Ru str. lies at 327 cm-1 on the SERS substrate AuOh, but this band shifts to 313 cm-1 on the AuRD and AuNC. The diruthenium moiety was reduced to [Ru2]4+ by the AuRD facet {110} and the AuNC {100}. The gold nanorods in the solution prepared with metal-string complexes bridging head-to-head on {111} facets were used for the SERS substrate. The SERS curves of the complexes in these self-assembled head-to-head rods display νRu-Ru str. at 327 cm-1, which is assigned to having an [Ru2]5+ core. Hence, facets {110} and {100} have a reduction reactivity greater than that of {111}. In Ru2Cu(dpa)4Cl2, the νRu-Ru str. is observed to lie at 312 cm-1 on AuRD, but shifts to 320 cm-1 on the AuNC and AuOh. In the latter cases, the diruthenium moiety was reduced to having a charge of 4+ with electronic configuration π*2δ*2, whereas the former case band at 312 cm-1 with a weaker Ru-Ru bonding is also attributed to [Ru2]4+ but with electron configuration π*4. π*4 lies at an energy greater than π*2δ*2. The electrochemical SERS spectra of diruthenium complexes were recorded to verify their oxidation states. Conclusively, these results yield the reduction reactivity of the following facet: {110} > {100} > {111}. According to the results of the redox reactions, the valence states of the diruthenium metal-string complexes are verified. In the [Ru2] n+ core, n = 4 π*4, 4 π*2δ*2, 5 π*2δ*, and 6 π*δ*, and the νRu-Ru str. is 312, 320, 327, and 337 cm-1, respectively.

Memantine Rescues Neurosyphilis-Related Schizophrenic-like Features and Cognitive Deficit.

OBJECTIVES: Neurosyphilis, an infectious neuroinflammatory disorder, could cause diverse neuropsychiatric symptoms mimicking disorders of schizophrenia and dementia; hence, it is known as the "chameleon of psychiatry." Here, we present a subject with neurosyphilis with schizophrenic features and share the treatment outcome. METHODS: A 42-year-old single man had schizophrenic-like features and cognitive dysfunction for 1 year. Neurosyphilis was confirmed by a cerebral spinal fluid study. The brain image revealed multiple punctuated white matter gliosis in the bilateral frontal lobes and old lacunar infarctions in the bilateral basal hippocampus. The neuropsychiatric functions were declined until adjunctive memantine therapy. RESULTS: With the add-on therapy of memantine 10 mg daily, the psychotic and dementic symptoms markedly improved, and the patient recovered to the premorbid state in the 2-year follow-up course. CONCLUSIONS: Memantine has an adjunctive effect on neurosyphilis-related neuropsychiatric disorder via modulation of the glutamatergic neurotransmission and microglia-induced neuroinflammation.

Photochemistry of Bacteriorhodopsin with Various Oligomeric Statuses in Controlled Membrane Mimicking Environments: A Spectroscopic Study from Femtoseconds to Milliseconds.

Preparing transmembrane protein in controllable lipid bilayers is essential for unravelling the coupling of the environments and its dynamic functions. Monomerized bacteriorhodopsin (mbR) embedded in covalently circularized nanodiscs was prepared with dimyristoylphosphatidylglycerol (DMPG) lipid and circular membrane scaffold proteins of two different sizes, cE3D1 and cΔ H5, respectively. The retinal photoisomerization kinetics and thermodynamic photocycle were examined by femtosecond and nanosecond transient absorption, respectively, covering the time scale from femtoseconds to hundreds of milliseconds. The kinetics of the retinal isomerization and proton migration from the protonated Schiff base to Asp-85 were not significantly different for monomeric bR solubilized in Triton X-100 or embedded in circularized nanodiscs. This can be ascribed to the local tertiary structures at the retinal pocket vicinity being similar among monomeric bR in various membrane mimicking environments. However, the aforementioned processes are intrinsically different for trimeric bR in purple membrane (PM) and delipidated PM. The reprotonation of the deprotonated Schiff base from Asp-96 in association with the decay of intermediate M, which involved wide-ranged structural alteration, manifested a difference in terms of the oligomeric statuses, as well as a slight dependence on the size of the nanodisc. In summary, bR oligomeric statuses, rather than the environmental factors, such as membrane mimicking systems and nanodisc size, play a significant role in bR photocycle associated with short-range processes, such as the retinal isomerization and deprotonation of protonated Schiff base at the retinal pocket. On the other hand, the environmental factors, such as the types of membrane mimicking systems and the size of nanodiscs, affect those dynamic processes involving wider structural alterations during the photocycle.

Sleep-disordered breathing, craniofacial development, and neurodevelopment in premature infants: a 2-year follow-up study.

INTRODUCTION: Sleep problems, neuro-developmental development, and sleep-disordered-breathing (SDB), are reported as more prevalent in premature infants than in full-term infants. We investigated the relationship between neuro-development, and SDB in preterm infants at 24 months corrected age (CA) with a narrow palatal presentation over time. METHODS: We enrolled infants 40 weeks or younger at birth collecting obstetric and birth data. Participants were followed up at 6, 12, 18, and 24 months CA. We evaluated craniofacial development by inspecting and photo documenting hard palate; sleep using sleep diary, actigraphy and night-time polysomnography-PSG-; and development using Bayley- Scales-of-Infant-Development and Denver-Developmental-Screening-Test (DDST) at each visit and comparing results at six months and two years. RESULTS: 244 premature infants [139 (57.0%) boys, [at birth: mean gestational age-GA- 31.5 ± 3.2 weeks, 1691.9 ± 593.9 g, 40.2 ± 5.2 cm], and 30 full term infants (50% boys), [mean GA 39.3 ± 1.0 weeks, 3131.0 ± 390.0 g, and 49.38 ± 2.0 cm] were enrolled in the study. At 6 and 24 months, 65.2% premature infants had a narrow hard palate (NHP). At 24 months, 79% had an apnea-hypopnea- index (AHI) > 1 events/hour at PSG, with a mean AHI of 3.00 ± 2.95. Only 10% of full term infants had NHP at birth and the mean AHI was 0.5 ± 0.2 event/hour at 24 months. CONCLUSION: Preterm infants have a higher occurrence of NHP at birth. At two years of age they have more sleep problems, most commonly associated with obstructive-SDB, and a higher rate of development delays. Frequency of NHP is still abnormally high, suggesting not only abnormal orofacial growth over-time, but also impact of this abnormal growth in the genesis of the obstructive-SDB.

Temperature-Controlled Thiation of α-Cyano-ß-Alkynyl Carbonyl Derivatives for De Novo Synthesis of 2-Aminothiophenes and Thieno[2,3- c]isothiazoles.

Making use of temperature-controlled thiation as a key operation, a simple route to 2-aminothiophenes or thieno[2,3- c]isothiazoles has been newly developed wherein the 2-aminothiophene nucleus was formed through an initial formation of thioamide followed by a 5-exo-dig addition to the tethered alkyne; however, under harsher thermal conditions, excess sulfur-transferring reagents enabled further oxidative thiation to generate the corresponding thieno[2,3- c]isothiazoles.

Ligand-Unsupported Cuprophilicity in the Preparation of Dodecacopper(I) Complexes and Raman Studies.

Synthesis and characterization of two dodecacopper(I) extended metal atom chains (EMAC) assembled by two hexadentate bis(pyridylamido)amidinate-supported hexacopper(I) string complexes (monomers) via the ligand-unsupported cuprophilicity are described. In addition to short unsupported Cu-Cu contacts, two hexacopper fragments in these two dodecacopper EMACs show a bent conformation based on X-ray crystallography. Compared with their THF-bound hexacopper(I) monomers and protonated ligands, these ligand-unsupported cuprophilic interactions are shown to be weak by Raman spectroscopy. DFT calculations suggest the ligand-unsupported cuprophilicity originate from weak attractive orbital interactions, and the strength is estimated to be 2.4 kcal mol-1 .

S- Cis Diene Conformation: A New Bathochromic Shift Strategy for Near-Infrared Fluorescence Switchable Dye and the Imaging Applications.

In this paper, we present a novel charge-free fluorescence-switchable near-infrared (IR) dye based on merocyanine for target specific imaging. In contrast to the typical bathochromic shift approach by extending π-conjugation, the bathochromic shift of our merocyanine dye to the near-IR region is due to an unusual S- cis diene conformer. This is the first example where a fluorescent dye adopts the stable S- cis conformation. In addition to the novel bathochromic shift mechanism, the dye exhibits fluorescence-switchable properties in response to polarity and viscosity. By incorporating a protein-specific ligand to the dye, the probes (for SNAP-tag and hCAII proteins) exhibited dramatic fluorescence increase (up to 300-fold) upon binding with its target protein. The large fluorescence enhancement, near-IR absorption/emission, and charge-free scaffold enabled no-wash and site-specific imaging of target proteins in living cells and in vivo with minimum background fluorescence. We believe that our unconventional approach for a near-IR dye with the S- cis diene conformation can lead to new strategies for the design of near-IR dyes.

Isomerization Reaction of mer- to fac-Tris(2-phenylpyridinato-N,C2')Iridium(III) Monitored by Using Surface-Enhanced Raman Spectroscopy.

We developed a new method by enclosing the complex tris(2-phenylpyridinato-N,C2')Iridium(III), Ir(ppy)3 with surfactant cetyltrimethylammonium bromide (CATB), coated with a thin layer of silica then bonded to the surface of silver nanoparticle. These samples were used to acquire surface-enhanced Raman scattering (SERS) spectra. The thickness of silica layer was controlled to have efficient phosphorescence quenching and Raman enhancement by metal nanoparticle. The SERS spectra of fac- and mer-Ir(ppy)3, recorded at 633 nm excitation, display distinct ring breathing mode features because the total symmetric vibrational bands were enhanced. This provides a convenient means to differentiate these isomers with great sensitivity and to study their isomerization process. A direct conversion reaction of mer- to fac- isomerization is identified with time constant 3.1 min when mer was irradiated with Xe light. Via thermal activation, under moderate conditions (pH 5.5 and 343 K), we observed an intermediate particularly with new bands 320/662 cm-1 after heating for 17.5 h, and then those bands disappeared to form fac-Ir(ppy)3. On the basis of DFT calculations, the intermediate is proposed to contain octahedral N-N Ir(ppy)3-HO-silica structure; band at 320 cm-1 is assigned to iridium oxygen stretching mode νIr-O of this intermediate. Under acidic conditions, pH 1-2 catalyzed by silanol in silica, byproduct with band at 353 cm-1 was observed. According to the SERS bands and the calculation, this byproduct is assigned to be iridium(III) siloxide, and the new band is assigned to νIr-O.

Excited state dynamics of symmetric and asymmetric Cr3(dpa)4Cl2 measured using femtosecond transient absorption spectroscopy.

Herein, the excited-state dynamics of an extended metal atom chain complex, Cr3(dpa)4Cl2 (dpa = dipyridylamide), in tetrahydrofuran solution were investigated using femtosecond transient absorption spectroscopy. Upon excitation at a wavelength of 330 nm, two distinct excited-state absorption species with varied dynamics were identified and assigned to the symmetric (s-) and unsymmetric (u-) Cr3(dpa)4Cl2. The major species is s-Cr3(dpa)4Cl2 that undergoes rapid conversion at less than 100 fs from the ligand-centred π-π* state, which is the initially accessed state, to the metal-centred d-d state and then vibrational cooling accompanying the structural relaxation at a time constant ∼2.2 ps. Most of the s-form is recovered to the ground state at ∼200 ps. For u-Cr3(dpa)4Cl2, a similar rapid conversion to d-d states is observed, and the geometric/vibrational relaxation is ∼0.8 ps. The second recovery of the ground state with approximately equal amplitude is observed at a time constant of ∼5 ns. This might be because many d-d states exist and about half of them inefficiently couple with the ground state surface.