APPLICATIONS OF H-ATOM QUANTUM-DIFFUSION REACTIONS IN SOLID PARA-HYDROGEN TO ASTROCHEMICAL STUDIES: FINDING A MYSTERIOUS LINK BETWEEN INTERSTELLAR ISOCYANIC ACID [HNCO] AND FORMAMIDE [H2NC(O)H]

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.6]{cycle.eps} \end{wrapfigure} Formamide [\chem{H_2NC(O)H}], the smallest molecule containing the biologically important peptide bond, was detected in the interstellar medium (ISM) almost 50 years ago. Recent observations have shown that a strong correlation between its abundance and that of isocyanic acid [\chem{HNCO}] exists in pre- and protostellar environments. It was proposed that this correlation is due to effective synthesis of formamide from \chem{HNCO} by consecutive H-atom addition reactions.\footnote{L\`{o}pez-Sepulcre, \textit{Montly Not. Roy. Astr. Soc.} \textbf{449}, 2438–2458 (2015).} However, Nobel \textit{et al.} showed that bombardment of \chem{HNCO} ice with H atoms led no formation of formamide.\footnote{Nobel, J. A., \textit{et al.}, \textit{Astron. Astrophys.} \textbf{576}, A91 (2015).} So far, no laboratory experiment or theoretical calculations can explain the linkage between these two species.\\ We utilized the advantages of the solid \textit{para-}H$_2$ quantum host to investigate the H-atom reactions linking \chem{HNCO} and formamide. Reactions of \chem{H_2NC(O)H} with H atoms lead to \chem{H_2NCO}, and subsequently \chem{HNCO}. Further hydrogenation reactions convert some HNCO back to \chem{H_2NCO} and \chem{H_2NC(O)H}; the reaction with \chem{D_2NC(O)H} clearly showed that these reactions took place. The correlation between the abundance of \chem{HNCO} and \chem{H_2NC(O)H} can hence be understood by a dual-cycle mechanism shown in the figure, which connects the two species by a quasi-equilibrium. This mechanism and its generalized form for other molecular pairs can also play an important role in the formation of interstellar H$_2$ from H atoms

Triggering near‐infrared luminescence of vanadyl phthalocyanine by charging

Probing electrofluorochromism (EFC) at the molecular level remains challenging. Here we study the strongly charge state‐dependent photoluminescence of vanadyl phthalocyanine. We report vibrationally resolved absorption and laser‐induced fluorescence (LIF) spectra of samples comprising both the mass‐selected neutral molecule (VOPc⋅, a stable radical) and its cation produced upon electron ionization (EI) isolated in 5 K neon matrices. Ionization of the essentially non‐emissive VOPc⋅ forms a high‐spin diradical cation (VOPc(+..)) which shows profound photoluminescence (PL) in the NIR range. This unique phenomenon is potentially of interest for NIR‐emitting electro‐optic devices

Photoactivated Refractive Index Anisotropy in Fluorescent Thiophene Derivatives

The optical control of anisotropy in materials is highly advantageous for many technological applications, including the real-time modulation of another light signal in photonic switches and sensors. Here, we introduce three thiophene derivatives with a donor-acceptor structure, which feature different positions of an electron-acceptor nitrile group, and both photoalignment and luminescence properties. Quantum chemical calculations highlight the presence of trans-forms stable at room temperature and metastable cis-isomers. Besides photoluminescence peaked at 440-460 nm and 0.4 ns lifetime, the three nonlinear optical chromophores exhibit photoinduced anisotropy of the refractive index closely depending on the specific molecular structure, with higher values of birefringence at lower driving signal being obtained for ortho substitution of the nitrile group. All-optical modulation of an external light beam at rates of hundreds of hertz is demonstrated in the fluorescent systems. This finding opens an interesting route to multispectral photonic switches embedded in the active layers of light-emitting devices

TTF based donor-pi-acceptor dyads synthesized for NLO applications

Two new TTF-pi-acceptor dyads that contain p-nitrophenyl group as acceptor and bis-(styryl)benzene system as an efficient π−conjugated bridge have been synthesized by multistep synthetic procedure and their electrochemical behavior has been studied by cyclic voltammetry (CV). The occurrence of an intramolecular charge transfer (ICT) in these molecules has been evidenced by UV–Visible electronic absorption spectroscopy and these studies were completed by DFT calculations in both gas phase and in solution. The nonlinear optical parameters obtained via SHG and THG measurements are described and indicate that these materials are valuable candidates for the construction of optoelectronic and photonic devices. The Optical Kerr Effect measurements indicate that these materials exhibit a great potential in the field of optical switchers construction, where the material\u27s photoresponse time is a crucial parameter

Pre-nucleation clusters as solute precursors in crystallisation

Crystallisation is at the heart of various scientific disciplines, but still the understanding of the molecular mechanisms underlying phase separation and the formation of the first solid particles in aqueous solution is rather limited. In this review, classical nucleation theory, as well as established concepts of spinodal decomposition and liquid–liquid demixing, is introduced together with a description of the recently proposed pre-nucleation cluster pathway. The features of pre-nucleation clusters are presented and discussed in relation to recent modifications of the classical and established models for phase separation, together with a review of experimental work and computer simulations on the characteristics of pre-nucleation clusters of calcium phosphate, calcium carbonate, iron(oxy)(hydr)oxide, silica, and also amino acids as an example of small organic molecules. The role of pre-nucleation clusters as solute precursors in the emergence of a new phase is summarized, and the link between the chemical speciation of homogeneous solutions and the process of phase separation via pre-nucleation clusters is highlighted

Photoinduced Birefringence in PMMA Polymer Doped with Photoisomerizable Pyrazoline Derivative

Upon S₀–S₁ excitation, the pyrazoline derivative molecule (<i>Z</i>)-2-(4-nitrophenyl)-3-(1-phenyl-4,5-dihydro-1<i>H</i>-pyrazol-3-yl)­acrylonitrile, abbreviated as PY-oCNNO₂, can be transformed from its ground state <i>trans</i> (<i>E</i>) form to bended <i>cis</i> (<i>Z</i>) form. Similar to the case of the well-known family of the photochromic azobenzenes, such a molecular property can be employed to fabrication of photochromic polymers by suitable doping of the chromophores into polymer matrix. In this work, we prepared poly­(methyl methacrylate) thin films doped with PY-oCNNO₂ and measured the characteristic for optical switchers dynamic and static photoinduced birefringence (PIB) phenomenon. Possible conformational states of PY-oCNNO₂, energy barriers, and associated dipole moments were calculated using TD-DFT quantum chemical methods. The presented experiments show that pyrazoline derivatives constitute a prospective group of materials with a great potential for photonic applications

Photo-Physical Transformations in Pyrazoline Derivative Based Systems

Discovery of <i>E</i>/<i>Z</i> or <i>trans</i>–<i>cis</i> photoisomerization in the azobenzenes and their derivatives had tremendous impact on the whole domain of photochromic materials including photochromic polymers and liquid crystals. Here we show similar configurational photoinduced transformation in a simple derivative of pyrazoline. The X-ray crystallographic investigations of (<i>E</i>)-3-(4-nitrostyryl)-1-phenyl-4,5-dihydro-1<i>H</i>-pyrazole (abbreviated as PY-pNO₂) in grown crystals show two different structures comprising of either <i>cis</i> or <i>trans</i> molecules. The performed quantum chemical calculations confirm the existence of both configurations of PY-pNO₂ at the room temperature. Photophysical properties of this compound derived from quantum chemical calculations predict possibility of <i>trans</i> to <i>cis</i> switching of PY-pNO₂ by light. Indeed, molecules of PY-pNO₂ embedded in PMMA polymeric matrix when illuminated with 532 nm linearly polarized laser light show the induced optical anisotropy, i.e., birefringence characteristic for photoisomerizable molecules similar to that in the group of the azobenzene derivatives