Imine-stabilized silylium ions: synthesis, structure and application in catalysis.

Novel norbornene-based imine-stabilized silylium ions 2 have been synthesized via the simple reaction of sulfide-stabilized silylium ion 1 with carbonyl derivatives. Those silylium ions were fully characterized in solution and in the solid state by NMR spectroscopy and X-ray diffraction analysis as well as DFT calculations. Unlike the previously reported phosphine-stabilized silylium ion VI, behaving as a Lewis pair, calculations show that 2 have a strong Lewis acid character. Indeed, imine-stabilized silylium ions 2 are able to activate Si-H bonds and catalyzed the hydrosilylation of carbonyl derivatives under mild conditions.

Reductive Elimination at Pb(II) Center of an (Amino)plumbylene-Substituted Phosphaketene: New Pathway for Phosphinidene Synthesis.

A stable (amino)plumbylene-substituted phosphaketene 3 was synthesized by the successive reactions of PbCl2 with two anionic reagents (lithium amidophosphine and NaPCO). Of particular interest, the thermal evolution of 3, at 80 °C, leads to the transient formation of corresponding amino- and phosphanylidene-phosphaketenes (6 and 7), via a reductive elimination at the PbII center forming new N-P and P-P bonds. Further evolution of 6 gives a new cyclic (amino)phosphanylidene phosphorane 4, which shows a unique reactivity as a phosphinidene. This result provides a new synthetic route to phosphinidenes, extending and facilitating further their access.

The effect of "on/off" molecular switching on the photophysical and photochemical properties of axially calixarene substituted activatable silicon(iv)phthalocyanine photosensitizers.

Silicon(iv) phthalocyanines ( and ) bearing two calixarene groups as axial ligands were synthesized. Surprisingly, both phthalocyanines were obtained as two different isomers ( and ) depending on the distance between calixarene benzene groups and the phthalocyanine ring. DFT and TD-DFT computations were performed to model plausible structures of these isomers and to simulate electronic absorption spectra. These isomers converted into each other depending on the polarity of the used solvent, temperature and light irradiation. The photophysical and photochemical properties of each isomer were investigated in dimethylsulfoxide (DMSO) for the determination of photodynamic therapy (PDT) activities of these compounds. The more blue-shifted isomers ( and ) showed higher fluorescence quantum yields and singlet oxygen generation compared to more red-shifted counterparts ( and ). This behavior is extremely important for developing activatable photosensitizers for cancer treatment by PDT. Although these photosensitizers produce lower singlet oxygen in normal cells, they produce higher singlet oxygen (six times higher for ) in cancer cells since these photosensitizers converted to more blue-shifted isomers by using light irradiation.

Effects of position (α or ß) and linker heteroatom (O or S) of substituent on the photophysicochemical behavior of poly(oxyethylene) substituted ZnPcs and assessment of J-aggregation or protonation using TD-DFT computations.

A series of zinc phthalocyanines (ZnPcs) tetra-substituted with 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanol () or 1,3-di[2-(2-ethoxyethoxy)ethoxy]-2-propanethiol () at peripheral (ß) () and non-peripheral (α) () positions have been synthesized and characterized. The spectroscopic, photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen generation and photodegradation) properties of these newly synthesized phthalocyanines have been investigated in DMSO. The effects of the position of the substituents on the phthalocyanine skeleton and the nature of the linker heteroatom on their spectroscopic, photophysical and photochemical properties have been determined. The quenching behavior of the zinc phthalocyanines by 1,4-benzoquinone has been studied in DMSO. All of the zinc(ii) Pc complexes ( and ) showed similar electronic absorption spectra in various solvents (chloroform, dichloromethane, DMF, DMSO, THF and toluene). However, complex gave an extra red-shifted band at 742 nm in chloroform and dichloromethane. DFT and TD-DFT computations were performed on the model structures (, and ) to find out the cause of the extra red-shifted Q band (J-type aggregation or protonation of the Pc ring). The computational results showed that monoprotonation of a meso nitrogen atom leads to the formation of this extra band. Photophysical and photochemical measurements indicated that these newly synthesized ZnPc derivatives are promising candidates for use as photosensitizers in the application of PDT.