Проектна діяльність бібліотек та інформаційних установ

Робоча навчальна програма «Проектна діяльність бібліотек та інформаційних установ» за напрямом підготовки 6.020102 «Книгознавство, бібліотекознавство і бібліографія», галузі знань 0201 «Культура», освітній рівень: перший (бакалаврський). - 2017 р

Design and Synthesis of Photodissociable Ligands Based on Azoimidazoles for Light-Driven Coordination-Induced Spin State Switching in Homogeneous Solution

Light-switchable azoimidazoles were rationally designed and synthesized, and their performance was investigated as photodissociable ligands (PDL) and for spin state switching of Ni porphyrins. The rationally designed ligands exhibit a high photochemical conversion rate (<i>trans</i> → <i>cis</i> > 98%) and no measurable fatigue over a large number of switching cycles at room temperature under air. As compared to the known phenylazopyridines, the phenylazoimidazoles exhibit a much stronger affinity as axial ligands to Ni porphyrin in the binding <i>trans</i> configuration and a low affinity in their <i>cis</i> form. This affinity switching was used to control the coordination number of Ni²⁺. Concomitant with the change in coordination number is the change of the spin state from triplet (high spin) to singlet state (low spin). We report on phenylazoimidazole-based PDLs that switch the paramagnetic ratio of the investigated nickel species by up to 70%. Consequently, azoimidazoles exhibit considerably higher switching efficiencies than previously described pyridine-based PDLs

Coordination-Induced Spin-State Switching with Nickel Chlorin and Nickel Isobacteriochlorin

We present the first coordination-induced spin-state switching with nickel chlorin and nickel isobacteriochlorin. The spin-state switching was monitored by UV–vis spectroscopy and NMR titration experiments. The association constants (<i>K</i>₁ and <i>K</i>₂) and thermodynamic parameters (Δ<i>H</i> and Δ<i>S</i>) of the coordination of pyridine were determined. The first X-ray analyses of a paramagnetic nickel chlorin and a nickel isobacteriochlorin provide further information about the structure of the octahedral complexes. Nickel chlorin and even more pronounced nickel isobacteriochlorin exhibit stronger coordination of axial ligands compared to the corresponding nickel porphyrin and thus provide the basis for more efficient spin-switching systems

Surface Control of Alkyl Chain Conformations and 2D Chiral Amplification

Trioctyl-functionalized triazatriangulenium (trioctyl-TATA) deposited on Au(111) and Ag(111) surfaces by electrospray ionization was investigated using low-temperature scanning tunneling microscopy. The molecule surprisingly adsorbs with gauche rather than anti conformations of the octyl groups. We observed chiral amplification in the islands. Only one of the eight possible configurations of the octyl groups was found in homochiral hexagonal networks. Quantum-chemical calculations confirmed and explained the preference for the gauche conformations of adsorbed trioctyl-TATA

Heterodiazocines: Synthesis and Photochromic Properties, <i>Trans</i> to <i>Cis</i> Switching within the Bio-optical Window

Diazocines, bridged azobenzenes, exhibit superior photophysical properties compared to parent azobenzenes such as high switching efficiencies, quantum yields, and particularly switching wavelengths in the visible range. Synthesis, however, proceeds with low yields, and derivatives are difficult to prepare. We now present two heterodiazocines which are easier to synthesize, and the general procedures should also provide facile access to derivatives. Moreover, both compounds can be switched with light in the far-red (650 nm). Accessibility and photophysical properties make them ideal candidates for applications such as photoswitchable drugs and functional materials

Ordered Monolayers of Free-Standing Porphyrins on Gold

The controlled attachment of chromo­phores to metal or semi­conducting surfaces is a prerequisite for the construction of photonic devices and artificial surface-based light-harvesting systems. We present an approach to mount porphyrins in ordered monolayers on Au(111) by self-assembly and verify it, employing STM, absorption spectroscopy, and quantum chemical calculations. The usual adsorption geometry of planar chromophores, flat on the surface or densely packed edge-on, is prevented by mounting the porphyrins upright on a molecular platform. An ethynyl unit as spacer and pivot joint provides almost free azimuthal rotation of the unsubstituted porphin. However, rotation of the larger tri­phenyl­porphyrin unit is sterically restricted: because the diameter of the substituted porphyrin is larger than the distance to its next neighbors, the phenyl substituents of neigboring molecules interact by dispersion force, which leads to an alignment of the azimuthal rotators

Photoswitchable Magnetic Resonance Imaging Contrast by Improved Light-Driven Coordination-Induced Spin State Switch

We present a fully reversible and highly efficient on–off photoswitching of magnetic resonance imaging (MRI) contrast with green (500 nm) and violet-blue (435 nm) light. The contrast change is based on intramolecular light-driven coordination-induced spin state switch (LD-CISSS), performed with azopyridine-substituted Ni-porphyrins. The relaxation time of the solvent protons in 3 mM solutions of the azoporphyrins in DMSO was switched between 3.5 and 1.7 s. The relaxivity of the contrast agent changes by a factor of 6.7. No fatigue or side reaction was observed, even after >100 000 switching cycles in air at room temperature. Electron-donating substituents at the pyridine improve the LD-CISSS in two ways: better photostationary states are achieved, and intramolecular binding is enhanced