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Tuneable Emission of Polyhedral Oligomeric Silsesquioxane‐ Based Nanostructures Self‐Assembled in the Presence of Europium(III) Ions: Reversible trans‐to‐cis Isomerization
摘要： Hybrids nanostructures with switchable and reversible “blue-red-green” emission were efficiently synthesized. The Polyhedral Oligomeric Silsesquioxane (POSS) behaves as a directional nano-cage for the terpyridine-based organic ligands allowing an easy complexation of Europium (III) cations. The complexes were characterized via UV-Vis and fluorescence spectroscopies and the stoichiometry was also confirmed via 1H NMR investigation. The octafunctionalized nano-cages allow forming novel self-assembled 3D architectures in presence of the lanthanide cation displaying a red-emission of particular intensity especially in solid state. The presence of an alkenyl group bridging the inorganic core to the organic moiety was employed to tune the emission properties via trans-cis isomerization of the double bond. In the case of O-POSS nanocages this isomerization was monitored also in presence of Eu(III) cations and was accompanied by an evident modification of the colour which passed from blue (trans-O-POSS) to red (Eu@trans-O-POSS) and finally to green (cis-O-POSS) as consequence of the release of the metal cations. This behaviour, together with the easy dispersion of the dry powder and the possibility of coating it as a film in presence of small amount of solvent, makes the emitting solid promising for applications in materials science.
关键词： europium,luminescence,silsesquioxanes,isomerization,self-assembly
更新于2025-11-14 15:32:45
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Esters of 4-nitrocinnamic acids and 4-halogene-4’-hydroxyazobenzenes – synthesis, mesogenic and optical studies
摘要： Six new compounds were synthesized that have no alkyl chains in their structure: 4-nitrocinnonates of 4-hydroxyazobenzene, 4-nitro-4'-hydroxyazobenzene, 4-fluoro-4'-hydroxyazobenzene, 4-chloro-4'-hydroxyazobenzene, 4-bromo-4'-hydroxyazobenzene, and 4-iodo-4'-hydroxyazobenzene. Using the polarizing microscopy and differential scanning calorimetry, enthalpies and temperatures of phase transitions were determined. All investigated compounds have an enantiotropic nematic phase. These compounds proved to be extremely thermally stable. Thermal decomposition was observed in temperatures above 300°C. Investigated compounds contain two different chromophore groups (i.e. azo and ethene moieties), which influenced the complex trans–cis isomerization processes of both groups (three time-separated processes were observed). It was shown that the presence of the ethene group significantly shifts the π-π* band towards higher energies. The substituent polarity in the azo group also affected the energy of this absorption band. A weak luminescence effect was observed in the 4-nitrocinnonates of 4-hydroxyazobenzene compound.
关键词： nematic,luminescence,Azobenzenes,trans–cis isomerization,polarizing microscopy,DSC calorimetry
更新于2025-09-23 15:23:52
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Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles (UCNPs) as mediator
摘要： Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in dark, or can be accelerated by exposing to illumination with longer wavelength typically in blue/green range. We present the application of lanthanide doped upconversion nanoparticles (UCNPs) to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm3+ or Er3+ as activator ions, the UCNPs provide emission in the spectral range of 450 nm < λem < 480 nm (for Tm3+, three and four photon induced emission) or 525 nm < λem < 545 nm (for Er3+, two photon induced emission), respectively. Especially for UCNPs containing Tm3+ a good overlap of the emission with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (λex= 976 nm) in the presence of the Tm3+-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13-times compared to thermal relaxation. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g., CHCl3) in contrast to water, which shows a distinct absorption in the NIR.
关键词： azobenzene containing surfactants,kinetic of cis-trans isomerization,up-conversion particles
更新于2025-09-23 15:23:52
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NEXMD Modeling of Photoisomerization Dynamics of 4-Styrylquinoline
摘要： Isomerization of molecular systems is ubiquitous in chemistry and biology, and is also important for many applications. Atomistic simulations can help determine the tunable parameters influencing this process. In this paper, we use the Nonadiabatic EXcited-state Molecular Dynamics (NEXMD) software to study the photoisomerization of a representative molecule, 4-styrylquinoline (SQ). Trans-SQ transforms into dihydrobenzophenanthridine (DHBP) upon irradiation with laser light, with the cis conformer acting as an intermediate. We study how varying three different external stimuli (i.e., apolar versus polar solvent, low versus high photoexcitation energy, and vacuum versus a constant temperature thermostat) affects the trans-to-cis photoisomerization of SQ. Our results show that polarization effects due to implicit solvation and the thermostat play a crucial role in the isomerization process, whereas photoexcitation energy plays a lesser role on the outcome and efficiency. We also show that NEXMD captures the correct energy profile between the ground and first singlet excited state, showing that there are two distinct reaction pathways to the final stable product that vary by the number of photons absorbed, in agreement with experiment. Ultimately, NEXMD proves to be an effective tool for investigating excited state single molecule dynamics subject to various environments and initial conditions.
关键词： Isomerization,Molecular Dynamics,NEXMD,4-styrylquinoline,Photoisomerization
更新于2025-09-23 15:21:21
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<i>In Vitro</i> Ligand Binding Kinetics Explains the Pharmacokinetics of [ <sup>18</sup> F]FE-PE2I in Dopamine Transporter PET Imaging
摘要： Two of the most popular positron emission tomography (PET) tracers, [11C]PE2I and [18F]FE-PE2I, used to quantify dopamine transporters (DAT), display dissimilar kinetic behavior in in vivo assays. This difference can be explained by comparing values of kinetic rate constants, which characterize interaction of these tracers with DAT sites in vitro. At the same time, this kinetic analysis showed that the overall binding mechanism is similar for these two tracers and includes a fast step of complex formation followed by a slow isomerization step of this complex. Comparison with previous PE2I data revealed that isomerization of the DAT complex with PE2I occurs three times faster than in the case of FE-PE2I, which leads to the slower onset of peak specific binding of the former tracer in the DAT-rich regions. Therefore, ligands with slower isomerization on-rate, including [18F]FE-PE2I, seem to be better tracers in vivo, and their properties can be predicted in vitro.
关键词： isomerization,ligand binding kinetics,FE-PE2I,Dopamine transporter,DAT,PET,PE2I
更新于2025-09-23 15:21:21
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Axisymmetric and Asymmetric Naphthalene-Bisthienothiophene Based Nonfullerene Acceptors: on Constitutional Isomerization and Photovoltaic Performance
摘要： Two pairs of constitutional isomers of fused-octacyclic nonfullerene acceptors (NFAs) based on a naphthalene-bisthienothiophene core with or without fluorination at the ending groups have been developed. Compared with the axisymmetric NFAs N66-IC and N66-2FIC with two six-member-ring bridges, their asymmetric constitutional isomers N65-IC and N65-2FIC both with one six-member-ring bridge and one five-member-ring bridge exhibit remarkable red-shifted absorption, higher crystallinity, and slightly down-shifted LUMO energy levels. Organic solar cells based on PBDB-T-2F:N65-2FIC achieved a promising power conversion efficiency of 10.19%, which is three times higher than that of its counterpart PBDB-T-2F:N66-2FIC cell (3.46%). While being blended with PBDB-T as the donor material, the asymmetric acceptor analogue N65-IC based solar cell pronounces a PCE of 9.03%, being significantly improved from that of 5.45% for the PBDB-T:N66-IC based cell, which is in consistency with the results from those cells from their both fluorinated donor and acceptor counterparts. Design rules on either both fluorinated, both non-fluorinated, or cross-combined donor/acceptors for device fabrication has been explored. In addition, PBDB-T-2F:N65-2FIC possesses very promising device stability with 85% of its initial PCE after an exposure time of 1500 h under one sun illumination, which is meaningful for their future commercial devices.
关键词： isomerization,naphthalene,organic solar cells,nonfullerene acceptors,asymmetry,axisymmetry
更新于2025-09-23 15:21:01
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Mechanism of the Laser Flash Photolysis of Rydimeric e-Tautomers of 4-N,N-Diethylaminoazobenzene in a 2-Propanol Medium
摘要： Difference transit absorption spectra (TASes) obtained via flash photolysis of isopropanol solutions of 4-N,N-diethylaminoazobenzene (DEAB) using 15 ns laser pulses at wavelengths of λex = 265 and 353 nm are analyzed. The inconsistency of constructing the mechanism of trans (t) → cis (c) photisomerization of DEAB based on the concept of this dye having a monomeric structure is shown. Based on the rydimeric concept of aminoazobenzene dyes, which include Rydberg dimers DEAB2, an adequate explanation is given of the nature of TAS signals with structures that change dramatically when in wavelength λex is altered. TAS signals of DEAB2 are compared to ultrahigh-speed (subpico- and pico-second) TAS signals of rydimers of a reference aminoazobenzene (AAB2) dye. It is established that the main difference between the structures of DEAB2 TAS signals generated by pulses with indicated wavelengths λex is due to the excitation of various rydimeric e-tautomers. In addition, a rydimeric e-tautomer that is unstable in the ground state acquires increased stability in propanol and, by absorbing radiation with λex = 353 nm, alters the structure of one of its monomers to quinoid while remaining a rydimer. It is shown that when excited with radiation pulses at λex = 265 nm, a rydimeric e-tautomer (which is more stable in the ground state) dissociates into individual monomers, one of which isomerizes to form cis-DEAB molecules.
关键词： diethylaminoazobenzene rydimers,rydimer photonics,laser flash photolysis,trans–cis isomerization,visible laser spectroscopy
更新于2025-09-23 15:21:01
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Flame Propagation Enhancement by Dielectric Barrier Discharge-Generated Intermediate Species
摘要： The interaction between nonthermal plasma (NTP) and fuel-air mixtures was studied both experimentally and by means of simulations, to elucidate their promotional effect on flame propagation. A promotional effect on flame propagation velocity was experimentally observed by generating a dielectric barrier discharge (DBD), prior to spark plug ignition of an n-heptane mixture in a high-pressure and -temperature environment, using a rapid compression and expansion machine (RCEM). A novel method of concentration calibration for mass-spectral analysis was conducted, to determine the intermediate species in the fuel-air mixtures passing through the DBD plasma. The effect of the intermediate chemical species on flame propagation was examined numerically using the PREMIX code, with the observed species being considered as initial additives in the calculations. The promotional effect was reproduced numerically with the addition of alkyl hydroperoxide to an n-heptane/air mixture; and the higher the temperature and leaner the mixture in the parameter region, the more pronounced was the effect. The promotional behavior was examined using reaction path analysis, on the basis of which enhanced low-temperature oxidation reactions, due to the dissociation of the alkyl hydroperoxide, were determined in pre-flame region.
关键词： dielectric barrier discharge,flame propagation velocity,Plasma-assisted combustion,low-temperature oxidation,isomerization
更新于2025-09-23 15:21:01
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Plasmon excitation and subsequent isomerization dynamics in naphthalene and azulene under fast proton interaction
摘要： The interaction of fast protons (velocity between 1.41 and 2.4 a.u.) with naphthalene and azulene is investigated as a model of an ion-polycyclic aromatic hydrocarbon interaction system. Production of various intact and fragment ions in coincidence with electron emission, electron transfer to projectile, or both is analyzed. The two targets being isomers, the rather obvious similarity in the fundamental ion-molecule collision energetics is quantitatively verified. The fast isomerization processes of cationic azulene are observed to be influencing its further dissociation channels such as C2H2 and H eliminations. A first ever attempt is presented here wherein single plasmon excitation in conjunction with isomerization dynamics is reported. Evidence from dication evaporation energetics is used to invoke the double plasmon excitation model. A model based on the multiplasmon resonance explains the observed proton velocity dependence of double to single ionization cross sections. Moreover an attempt is made to reinforce the proposition of double plasmon excitation by explaining the observed suppression of neutral H loss from dications as opposed to monocations.
关键词： double plasmon excitation,isomerization dynamics,naphthalene,azulene,ion-polycyclic aromatic hydrocarbon interaction,plasmon excitation,fast protons
更新于2025-09-23 15:21:01
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Nonconstant Enthalpy of thermosetting solid-solid Phase Change Materials Controlled by Light
摘要： Phase change materials (PCMs) based on the principle of latent heat thermal energy storage have been highly concerned by researchers and widely developed in various fields. However, for traditional PCMs, especially thermosetting solid-solid change materials (SSPCMs) which usually consist of crosslinking structure, the phase change enthalpy was fixed once the materials were constructed. To turn the constant enthalpy into adjustable one, we incorporated the light-sensitive methyl red (MR) groups into polyurethane-based SSPCMs. The MR-containing SSPCMs exhibit amplified enthalpy and increased melting temperature (Tm) after activated by UV light compared with the inactivated ones. UV treatment can promote the crystallization of the soft segment in polyurethane due to the light-induced isomerization of MR groups and visible light causes reverse effect of the activated samples that the enthalpy, Tm and crystallization get back to the original degree, which indicates the nonconstant enthalpy. A separation theory was proposed to explain the increased enthalpy and Tm caused by the cis configuration of MR groups.
关键词： nonconstant enthalpy,methyl red,separation theory,isomerization,irradiation
更新于2025-09-23 15:19:57