Solvent- and Light-Sensitive AIEE-Active Azo Dye: From Spherical to 1D and 2D Assemblies

Fluorescent molecular assembly systems provide an exciting platform for creating stimuli-responsive nano- and microstructured materials with optical, electronic, and sensing functions. To understand the relationship between (i) the plausible molecular structures preferentially adopted depending on the solvent polarity (such as N,N-dimethylformamide [DMF], tetrahydrofuran [THF], and toluene), (ii) the resulting spectroscopic features, and (iii) self-assembled nano-, micro-, and macrostructures, we chose a sterically crowded triangular azo dye (3Bu) composed of a polar molecular core and three peripheral biphenyl wings. The chromophore changed the solution color from yellow to pink-red depending on the solvent polarity. In a yellow DMF solution, a considerable amount of the twisted azo form could be kept stable with the help of favorable intermolecular interactions with the solvent molecules. By varying the concentration of the DMF solution, the morphology of self-assembled structures was transformed from nanoparticles to micrometer-sized one-dimensional (1D) structures such as sticks and fibers. In a pink-red toluene solution, the periphery of the central ring became more planar. The resulting significant amount of the keto-hydrazone tautomer grew into micro- and millimeter-sized 1D structures. Interestingly, when THF-H2O (1:1) mixtures were stored at a low temperature, elongated fibers were stacked sideways and eventually developed into anisotropic two-dimensional (2D) sheets. Notably, subsequent exposure of visible-light-irradiated sphere samples to solvent vapor resulted in reversible fluorescence off↔on switching accompanied by morphological restoration. These findings suggest that rational selection of organic dyes, solvents, and light is important for developing reusable fluorescent materials.

The Detection of a Hot Molecular Core in the Extreme Outer Galaxy

Interstellar chemistry in low-metallicity environments is crucial to understand chemical processes in the past metal-poor universe. Recent studies of interstellar molecules in nearby low-metallicity galaxies have suggested that metallicity has a significant effect on the chemistry of star-forming cores. Here we report the first detection of a hot molecular core in the extreme outer Galaxy, which is an excellent laboratory to study star formation and the interstellar medium in a Galactic low-metallicity environment. The target star-forming region, WB 89–789, is located at a galactocentric distance of 19 kpc. Our Atacama Large Millimeter/submillimeter Array observations in 241–246, 256–261, 337–341, and 349–353 GHz have detected a variety of carbon-, oxygen-, nitrogen-, sulfur-, and silicon-bearing species, including complex organic molecules (COMs) containing up to nine atoms, toward a warm (>100 K) and compact (<0.03 pc) region associated with a protostar (∼8 × 103 L ☉). Deuterated species such as HDO, HDCO, D2CO, and CH2DOH are also detected. A comparison of fractional abundances of COMs relative to CH3OH between the outer Galactic hot core and an inner Galactic counterpart shows a remarkable similarity. On the other hand, the molecular abundances in the present source do not resemble those of low-metallicity hot cores in the Large Magellanic Cloud. The results suggest that great molecular complexity exists even in the primordial environment of the extreme outer Galaxy. The detection of another embedded protostar associated with high-velocity SiO outflows is also reported.

Is There Any Linkage between Interstellar Aldehyde and Alcohol?

It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA cycle 4 data of a hot molecular core, G10.47+0.03, are utilized for this study. Various aldehydes (acetaldehyde, propanal, and glycolaldehyde), alcohols (methanol and ethylene glycol), and a ketone (acetone) are identified in this source. The excitation temperatures and column densities of these species were derived via the rotation diagram method assuming local thermodynamic equilibrium conditions. An extensive investigation is carried out to understand the formation of these species. Six pairs of aldehyde–alcohol are considered for this study: (i) methanal and methanol, (ii) ethanal and ethanol, (iii) propanal and 1-propanol, (iv) propenal and allyl alcohol, (v) propynal and propargyl alcohol, and (vi) glycolaldehyde and ethylene glycol. One pair of ketone–alcohol (acetone and isopropanol) and ketene–alcohol (ethenone and vinyl alcohol) are also considered. Two successive hydrogenation reactions in the ice phase are examined to form these alcohols from aldehydes, ketone, and ketene, respectively. Quantum chemical methods are extensively executed to review the ice-phase formation route and the kinetics of these species. Based on the obtained kinetic data, astrochemical modeling is employed to derive the abundances of these aldehydes, alcohols, ketone, and ketene in this source. It is seen that our model could successfully explain the observed abundances of various species in this hot molecular core.

M17 MIR: A Massive Protostar with Multiple Accretion Outbursts *

We report the discovery of a massive protostar M17 MIR embedded in a hot molecular core in M17. The multiwavelength data obtained during 1993–2019 show significant mid-IR (MIR) variations, which can be split into three stages: the decreasing phase during 1993.03–mid-2004, the quiescent phase from mid-2004 to mid-2010, and the rebrightening phase from mid-2010 until now. The variation of the 22 GHz H2O maser emission, together with the MIR variation, indicates an enhanced disk accretion rate onto M17 MIR during the decreasing and rebrightening phases. Radiative transfer modeling of the spectral energy distributions of M17 MIR in the 2005 epoch (quiescent) and 2017 epoch (accretion outburst) constrains the basic stellar parameters of M17 MIR, which is an intermediate-mass protostar (M * ∼ 5.4 M ⊙) with M ̇ acc ∼ 1.1 × 10 − 5 M ⊙ yr − 1 in the 2005 epoch and M ̇ acc ∼ 1.7 × 10 − 3 M ⊙ yr − 1 in the 2017 epoch. The enhanced M ̇ acc during outburst induces the luminosity outburst ΔL ≈ 7600 L ⊙. In the accretion outburst, a larger stellar radius is required to produce M ̇ acc consistent with the value estimated from the kinematics of H2O masers. M17 MIR shows two accretion outbursts (Δt ∼ 9–20 yr) with outburst magnitudes of about 2 mag, separated by a 6 yr quiescent phase. The accretion outburst occupies 83% of the time over 26 yr. The accretion rate in outburst is variable with amplitude much lower than the contrast between quiescent and outburst phases. The extreme youth of M17 MIR suggests that minor accretion bursts are frequent in the earliest stages of massive star formation.

The Irradiation of Methyl Cyanide (CH3CN) Ice at 15 K with 200 keV

&lt;p&gt;Methyl cyanide (CH&lt;sub&gt;3&lt;/sub&gt;CN) is the simplest of the organic nitriles found in space. It was first identified in the molecular clouds&lt;strong&gt;, &lt;/strong&gt;Sagittarius Sgr A and Sgr B in 1971, through its emission lines in the vicinity of 2.7 mm from the &lt;em&gt;J&lt;/em&gt; = 6 &amp;#174; 5 transition. In 1974 it was also reported in comet Kohoutek. CH&lt;sub&gt;3&lt;/sub&gt;CN, has since been detected in the Hale Bopp comet and, as of 2009, there are no less than 58 hot molecular core objects in which CH&lt;sub&gt;3&lt;/sub&gt;CN had been found. Methyl cyanide has also been discovered beyond the Milky Way galaxy, in the NGC 253 galax, which lies in the local group of galaxies, some 10 million light-years from Earth&lt;sup&gt;[1]&lt;/sup&gt;. It has also been detected in the interstellar medium (ISM) where it is thought to be made on the grain mantles.&lt;/p&gt; &lt;p&gt;Upon irradiation of the Irradiation of methyl cyanide (CH&lt;sub&gt;3&lt;/sub&gt;CN) ice at 15 K with 200 keV Protons, we observed several compounds. Although this experiment was conducted under different conditions than comparable ones carried out by other researchers (eg Hudson and Moore 2004; Hudson, Moore et al. 2008), similar results were obtained. The objectives were to determine which molecules would form upon irradiation of CH&lt;sub&gt;3&lt;/sub&gt;CN ice. The astrophysical ice of CH&lt;sub&gt;3&lt;/sub&gt;CN is present in the ISM, comets, solar bodies (&lt;em&gt;eg&lt;/em&gt; Titan) and other galaxies. These places receive radiation fluxes from levels of only a few eV to in excess of MeV cm&lt;sup&gt;-2&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;, the result being that complex molecules are formed - &lt;em&gt;eg&lt;/em&gt; HCN/CN&lt;sup&gt;-&lt;/sup&gt;, HCCCN, H&lt;sub&gt;2&lt;/sub&gt;C=C=NH and CH&lt;sub&gt;4&lt;/sub&gt;. This experiment was carried out using 200 keV protons, and so replicated a particular radiation level similar to that present in space. It was discovered that, upon the irradiation of CH&lt;sub&gt;3&lt;/sub&gt;CN under laboratory conditions, the same molecules as Hudson &lt;em&gt;et al &lt;/em&gt;2004 were formed. These molecules may then play an important role in the wider astrobiological context. For instance, HCN is vital in the formation of nitrogenous compound.&lt;/p&gt; &lt;div&gt;&lt;br /&gt; &lt;div&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;p&gt;Please insert your abstract HTML here.&lt;/p&gt;

Photochemical Properties and Stability of BODIPY Dyes

The present study is devoted to the combined experimental and theoretical description of the photophysical properties and photodegradation of the new boron-dipyrromethene (BODIPY) derivatives obtained recently for biomedical applications, such as bacteria photoinactivation (Piskorz et al., Dyes and Pigments 2020, 178, 108322). Absorption and emission spectra for a wide group of solvents of different properties for the analyzed BODIPY derivatives were investigated in order to verify their suitability for photopharmacological applications. Additionally, the photostability of the analyzed systems were thoroughly determined. The exposition to the UV light was found first to cause the decrease in the most intensive absorption band and the appearance of the hypsochromically shifted band of similar intensity. On the basis of the chromatographic and computational study, this effect was assigned to the detachment of the iodine atoms from the BODIPY core. After longer exposition to UV light, photodegradation occurred, leading to the disappearance of the intensive absorption bands and the emergence of small intensity signals in the strongly blue-shifted range of the spectrum. Since the most intensive bands in original dyes are ascribed to the molecular core bearing the BF2 moiety, this result can be attributed to the significant cleavage of the BF2 ring. In order to fully characterize the obtained molecules, the comprehensive computational chemistry study was performed. The influence of the intermolecular interactions for their absorption in solution was analyzed. The theoretical data entirely support the experimental outcomes.

New-Generation Liquid Crystal Materials for Application in Infrared Region

This study presents 13 new organic compounds with self-assembling behavior, which can be divided into two groups. The first synthesized group includes compounds based on 4′-(trifluoromethoxy)-[1,1′-biphenyl]-4-yl-4-(trifluoromethoxy) benzoate core, and the second includes compounds based on 4-((4-(trifluoromethoxy)phenyl)ethynyl)phenyl-4-(trifluoromethoxy) benzoate core. They differ in the number and location of the fluorine atom in the lateral position. Mesomorphic properties, phase transition enthalpies, refractive indices, birefringence, and MWIR (mid-wavelength infrared) spectral properties of the compounds were investigated, and the results were compared with currently used materials. The influence of the length of the core as well as type and position of substituents in the molecular core was analyzed. The lack of aliphatic protons in the molecular structure generated unique infrared properties.

Spin Seebeck effect of correlated magnetic molecules

In this paper we investigate the spin-resolved thermoelectric properties of strongly correlated molecular junctions in the linear response regime. The magnetic molecule is modeled by a single orbital level to which the molecular core spin is attached by an exchange interaction. Using the numerical renormalization group method we analyze the behavior of the (spin) Seebeck effect, heat conductance and figure of merit for different model parameters of the molecule. We show that the thermopower strongly depends on the strength and type of the exchange interaction as well as the molecule’s magnetic anisotropy. When the molecule is coupled to ferromagnetic leads, the thermoelectric properties reveal an interplay between the spin-resolved tunneling processes and intrinsic magnetic properties of the molecule. Moreover, in the case of finite spin accumulation in the leads, the system exhibits the spin Seebeck effect. We demonstrate that a considerable spin Seebeck effect can develop when the molecule exhibits an easy-plane magnetic anisotropy, while the sign of the spin thermopower depends on the type and magnitude of the molecule’s exchange interaction.

Multi-Scale Coherent Magnetic Field from Atomic Medium to L1544 Molecular Core

Magnetic fields play an important role in the evolution of interstellar medium and star formation. As the only direct tracer of interstellar field strength, credible Zeeman measurements remain sparse due to rather limited number of spectral lines with discernible Zeeman effect, particularly for cold, molecular gas. Here we report the detection of a magnetic field of 3.8 ± 0.3 μG through a new tracer, the HI narrow self-absorption (HINSA), toward the prestellar core L1544 of the Taurus molecular cloud using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). A combined analysis of the Zeeman measurements of quasar HI absorption, HI emission, OH emission, and HINSA reveals a coherent magnetic field from the atomic cold neutral medium (CNM) to the molecular envelope of the L1544. We find that the molecular envelope traced by HINSA is already magnetically supercritical, with a field strength comparable to that in the surrounding diffuse, magnetically subcritical CNM despite a large increase in density. The reduction of the magnetic flux relative to the mass, necessary for star formation, thus seems to happen during the transition from the diffuse CNM to the molecular gas traced by HINSA, earlier than envisioned in the classical picture where magnetically supercritical cores capable of collapsing into stars form out of magnetically subcritical envelopes. The HINSA Zeeman effect opens up a new window on the interstellar magnetic field that is poised for rapid growth in the era of Square Kilometer Array and its precursors.