Raman and Raman optical activity (ROA), IR, and vibrational circular dichroism (VCD) spectra of (R)- and (S)-pantolactone have been recorded in three solvents. ROA has been employed on water and DMSO ...solutions, VCD on DMSO and CCl4 solutions. In the last solvent, monomer–dimer equilibrium is present. Due to the low conformational flexibility of the isolated molecule and to the possibility of aggregation, this compound has been used here to test different protocols for computation of the spectroscopic responses taking into account solvent effects. Molecular dynamics (MD) simulations have been carried out together with statistical clustering methods based on collective variables to extract the structures needed to calculate the spectra. Quantum mechanical DFT calculations based on PCM are compared with approaches based on different representations of the solvent shell (MM or QM level). Appropriate treatment of the solvent permits obtaining of good band-shapes, with the added advantage that the MD analysis allows one to take into account flexibility of dimeric structures justifying the broadness of observed bands and the absence of intense VCD couplets in the carbonyl and OH stretching regions.
A new 1,2-dialkylquinoxaline-fused 7carbohelicene (7Hl-NAIQx) was designed and synthesized by asymmetrically introducing two alkyl chains onto the quinoxaline unit. Direct alkylation of the ...quinoxaline ring of quinoxaline-fused helicene leads to discontinuity in the conjugated structure. In the single-crystal analysis, the parent quinoxaline-fused 7carbohelicene (7Hl-Qx) was found to have a helical structure formed by two phenanthrene units and a nonplanar twisted angle between the phenanthrene and quinoxaline units. In contrast, 7Hl-NAIQx possesses an almost planar aromatic structure between the alkyl-quinoxaline and phenanthrene units (torsion angle: 179°), in addition to the similar helical structure between the two phenanthrene units. The steady-state absorption, fluorescence, and circular dichroism (CD) spectra of 7Hl-NAIQx were significantly red-shifted compared to those of 7Hl-Qx and 7carbohelicene (7Hl). These spectral changes were mainly explained by electrochemical measurements and density functional theory calculations. Moreover, the absolute fluorescence quantum yield (ΦFL) of 7Hl-NAIQx was 0.25, which is more than 10 times larger than that of the reference 7Hl (ΦFL = 0.02). Such a large enhancement of the fluorescence of 7Hl-NAIQx has provided excellent circularly polarized luminescence (CPL). The value of the anisotropy factor g lum (normalized difference in emission of right-handed and left-handed circularly polarized light) was estimated to be 4.0 × 10–3. The electroluminescence of an organic light-emitting diode utilizing 7Hl-NAIQx was successfully observed.
A series of fluorescent “push‐pull” tetrathia9helicenes based on quinoxaline (acceptor) fused with tetrathia9helicene (donor) derivatives was synthesized for control of the excited‐state dynamics and ...circularly polarized luminescence (CPL) properties. In this work, introduction of a quinoxaline onto the tetrathia9helicene skeleton induced the “push–pull” character, which was enhanced by further introduction of an electron‐releasing Me2N group or an electron‐withdrawing NC group onto the quinoxaline unit (denoted as Me2N‐QTTH and NC‐QTTH, respectively). These trends were successfully discussed in terms of by electrochemical measurements and density functional theory (DFT) calculations. As a consequence, significant enhancements in the fluorescence quantum yields (ΦFL) were achieved. In particular, the maximum ΦFL of Me2N‐QTTH was 0.43 in benzene (NC‐QTTH: ΦFL=0.30), which is more than 20 times larger than that of a pristine tetrathia9helicene (denoted as TTH; ΦFL=0.02). These enhancements were also explained by kinetic discussion of the excited‐state dynamics such as fluorescence and intersystem crossing (ISC) pathways. Such significant enhancements of the ΦFL values thus enabled us to show the excellent CPL properties. The value of anisotropy factor gCPL (normalized difference in emission of right‐handed and left‐handed circularly polarized light) was estimated to be 3.0×10−3 for NC‐QTTH.
Controlled push–pull: A series of fluorescent “push–pull” thiahelicenes based on quinoxaline‐fused tetrathia9helicene derivatives was synthesized to control the excited state dynamics and circularly polarized luminescence properties. The maximum ΦFL values of 0.43 and 0.30 were obtained in benzene.
A series of 5carbohelicene derivatives substituted by electron-withdrawing maleimide and electron-donating methoxy, such as maleimide-substituted 5carbohelicene (HeliIm) and methoxy-substituted ...HeliIm (MeO-HeliIm), were newly designed and synthesized to examine the electrochemical properties, excited-state dynamic and circularly polarized luminescence (CPL). First, electrochemical measurements and DFT calculations of 5carbohelicene derivatives were performed by comparing with the structural isomers: picene derivatives. Introduction of an electron-withdrawing maleimide group onto a 5carbohelicene core contributes to the stabilized LUMO state in HeliIm as compared to that of 5carbohelicene (Heli), whereas the energy level of HOMO state in MeO-HeliIm increases by introducing electron-donating methoxy (MeO) groups onto a HeliIm skeleton. The HOMO–LUMO gap of MeO-HeliIm is smaller than those of HeliIm and Heli, which is similar to the steady-state spectroscopic measurements. The absolute fluorescence quantum yield (ΦFL) of HeliIm (0.37) largely increased as compared to 5carbohelicene, Heli (0.04), whereas ΦFL of MeO-HeliIm (0.22) was slightly smaller than that of HeliIm. Theses photophysical processes including intersystem crossing are successfully explained by the kinetic discussions. Since 5carbohelicene derivatives show the chirality, measurements of circular dichroism (CD) and circularly polarized luminescence (CPL) were successfully performed. In particular, HeliIm and MeO-HeliIm have provide excellent circularly polarized luminescence (CPL) and the values of the anisotropy factor g lum were estimated to be ∼2.4 × 10–3 and ∼2.3 × 10–3, relatively. This is the first observation of CPL in 5carbohelicene derivatives.
Porous zirconia medium (PZrM) has been fabricated successfully using polystyrene microparticles (MPs) as templates. The emission spectra of rhodamine B (RhB) optical amplifying medium loaded inside ...PZrM porous scatterers were obtained at numerous excitation light intensities. The lasing thresholds (
I
th
) have been determined experimentally from the variations in the intensity of random laser oscillation peaks, which are suitably separated from the measured emission spectra.
I
th
is closely related to the pore sizes of PZrM and the added amount of PZrM powder, and it clearly provided the minimum against the pore size. This fact is explained reasonably by the simulation of scattering efficiency on the basis of the Mie scattering theory. Consequently, PZrM as a porous scatterer is superior to Zr MPs from the viewpoint of random laser oscillation.
Porous zirconia medium as a porous scatterer was superior to zirconia microparticles with respect to random laser oscillation.
Tetrasulfone9helicene (PTSH) was newly synthesized to improve and evaluate its fluorescence and excited-state dynamics through a single-step oxidation reaction of tetrathia9helicene (PTTH). In ...electrochemical measurements, the reduction potential of PTSH was shifted in a positive direction by approximately 1.0 V when compared to that of PTTH because of its electron-accepting sulfone units. The results of the electrochemical measurements agree with the energy levels calculated by density functional theory (DFT) methods and steady-state spectroscopic measurements. Furthermore, a significant enhancement of the absolute fluorescence quantum yield (ΦFL) was achieved. The absolute fluorescence quantum yield of PTSH attained 0.27, which is approximately 10 times larger than that of PTTH (ΦFL = 0.03). Such an enhancement of ΦFL can be successfully explained by the corresponding kinetic comparison. The reason is mainly the increased energy gap Δ E ST between the lowest singlet (S1) and triplet (T1) excited states. Finally, excellent circularly polarized luminescence of PTSH was also observed. The value of the anisotropy factor g CPL was estimated to be 8.3 × 10–4 in PTSH.
The aim of this study was to investigate the effects of artificial saliva on permeability measured using a highly sensitive digital flow meter of dentin discs treated with a phosphate containing ...desensitizer compound (Teethmate desensitizer; TD). Four random groups (n=10) were treated either with TD or distilled water (DW), then stored in artificial saliva (AS) or DW for 1 day, 1 week and 1 month. Flow rates under 2 kPa pressure were calculated as percentage reduction (PR%) from the baseline. The PR% of TD/AS group was significantly lower after 1 day and 1 week, but the PR%s of 1 month groups among TD/AS, TD/DW and DW/AS were not significantly different. The SEM photograph of TD/AS group displayed that the dentin surface was densely covered with mineral deposits. Ca and phosphate ions from the artificial saliva could penetrate into the tubules and precipitate as hydroxyapatite, resulting in the reduction in permeability.
5,10,15,20-Tetrakis(2,4,6-trimethylphenyl)-6‘-carboxyquinoxalino2,3-βporphyrinatozinc (II) (ZnQMA) and 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)-6‘,7‘-dicarboxyquinoxalino2,3-βporphyrinatozinc (II) ...(ZnQDA) have been synthesized to evaluate the effects of β,β‘-carboxyquinoxalino moieties on the structure and optical, electrochemical, and photovoltaic properties of the porphyrins. Both ZnQMA and ZnQDA exhibited broadened and red-shifted light absorption in UV−visible absorption spectra compared with 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrinatozinc (II) (ZnP). ZnQMA and ZnQDA also showed decrease in the highest occupied molecular orbital−lowest unoccupied molecular orbital (HOMO−LUMO) gap due to the extension of the porphyrin π-system. From the results of 1H NMR spectroscopy and DFT calculations, ZnQMA and ZnQDA were found to adopt saddle and planar structures, respectively. ZnQMA-sensitized TiO2 solar cell with TiO2 nanoparticles (P25) revealed the power conversion efficiency (η) of 5.2%, whereas ZnQDA-sensitized cell showed η = 4.0%. The superior performance of the ZnQMA-sensitized solar cell to the ZnQDA-sensitized one is originated from both the more favorable electron injection and charge collection efficiency.
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•ABA-type block copolymers containing hydrophilic zwitterionic segments were prepared.•Nano phase-separated surfaces with different hydrophobic domain sizes were prepared.•Protein ...adsorption was related to hydrophobic domain size and size of proteins.
In protein adsorption on material surfaces, the surface structure at the nanometer-scale is one of the most important factors; however, the relationship between the size of the hydrophobic protein-adsorptive domain and that of the protein in protein adsorption remains unclear. In this study, we prepared phase-separated surfaces with different hydrophobic domain sizes (10 or 20 nm) using amphiphilic ABA-type block copolymers composed of hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and hydrophobic poly(3-methacryloyloxy propyltris(trimethylsilyloxy) silane) (PMPTSSi) to investigate the adsorption behavior of proteins, including fibronectin, fibrinogen, and lysozyme. The hydrophobic PMPTSSi domain promotes protein adsorption, whereas the PMPC domain suppresses this. Compared with the uniform hydrophobic PMPTSSi surface, fibronectin and fibrinogen were not adsorb on the phase-separated surfaces, while lysozymes adsorbed only partly, indicating that proteins smaller than nanoscale hydrophobic domains adsorbed on the phase-separated surface. Moreover, the protein adsorption behavior and circular dichroism spectra analysis suggest that lysozyme densely adsorbed on the hydrophobic domain like a multi-layer, and that denature on the surface was promoted. This study contributes to the understanding of protein adsorption at nanoscale interfaces and designing biomaterials.
Phthalocyanines (Pcs) offer a high architectural flexibility in structure, which facilitates the tailoring of their physical, optoelectronic and chemical parameters over a very broad range. This ...tutorial review describes the recent advances in the synthesis of soluble axially substituted or bridged gallium phthalo- and naphthalocyanine compounds, and their photophysical and nonlinear optical properties. The exploitation of the chemical reactivity of the Ga-Cl bond can allow the preparation of a series of highly soluble axially substituted and bridged Pc complexes. Axial substituents in Pcs influence favourably nonlinear optical absorption for the presence of a dipole moment perpendicular to the macrocycle in the axially substituted phthalocyanines. All Z-scans performed exhibit a decrease of transmittance about the focus typical of an induced positive nonlinear absorption of incident light. Substitution and dimerization of the phthalocyanine monomer resulted in significant reductions in the saturation energy density of the material displaying clear evidence of the usefulness of structurally modifying the gallium phthalocyanine unit. Similar to indium phthalocyanines, gallium phthalocyanines are also among the most promising materials that have been investigated as limiters of intense light and the current series presents a selection of structural modifications useful for varying their nonlinear optical properties.
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![Highly Fluorescent [7]Carbo...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1932-7447/small "Highly Fluorescent [7]Carbohelicene Fused by Asymmetric 1,2-Dialkyl-Substituted Quinoxaline for Circularly Polarized Luminescence and Electroluminescence")
