No abstract

Mesoporous carbon nitrides, silicas and their composites have been prepared by a combined sol-gel and thermal condensation approach. Precursors for the carbon nitride (cyanamide) and silica (TEOS) are mixed and condensed simultaneously. After condensation and heat treatment it is observed that the carbon nitride and silica formed highly interpenetrating mesophases which leads either to the formation of mesoporous carbon nitride or silica after selective removal of one of the phases. Importantly, the carbon nitride preserves its graphitic stacking even in the spatial confinement introduced by the surrounding silica phase. As both precursors are liquids this approach allows convenient shaping into thin and thick films or monoliths of mesoporous carbon nitrides. Enhanced photocatalytic activity is observed for the production of hydrogen from water when these mesoporous carbon nitrides are applied as photocatalyst in comparison to the bulk, but also to other mesoporous carbon nitrides, prepared by the reported two-step, hard templating approach.

The optically active states in a novel (terpyridine)Ru(4H-imidazole) complex displaying an unusually broad and red-shifted absorption in the visible range are investigated experimentally and theoretically. Since this property renders the complex promising for an application as sensitizer in dye-sensitized solar cells, a detailed knowledge on the correlation between features in the absorption spectrum and structural elements is indispensable in order to develop strategies for spectroscopy/theory-guided design of such molecular components. To this aim, time-dependent density functional theory calculations, including solvent effects, are employed to analyze the experimental UV-vis absorption and resonance Raman (RR) spectra of the unprotonated and protonated forms of the complex. This provides a detailed photophysical picture for a complex belonging to a novel class of Ru-polypyridine black absorbers, which can be tuned by external pH stimuli. The complex presents two absorption maxima in the visible region, which are assigned by the calculations to metal-to-ligand charge transfer (MLCT) and intra-ligand states, respectively. RR simulations are performed in resonance with both bands and are found to correctly reproduce the observed effects of protonation. Finally, the examination of the molecular orbitals and of the RR spectra for the MLCT state shows that protonation favors a charge transfer excitation to the 4H-imidazole ligand.

Novel phenylazole ligands were applied successfully in the synthesis of cyclometalated iridium(III) complexes of the general formula [Ir(phenylazole)(2)(bpy)]PF(6) (bpy=2,2'-bipyridine). All complexes were fully characterized by NMR, IR, and MS spectroscopic studies as well as by cyclic voltammetry. Three crystal structures obtained by X-ray analysis complemented the spectroscopic investigations. The excited-state lifetimes of the iridium complexes were determined and showed to be in the range of several hundred ns to multiple µs. All obtained iridium complexes were active as photosensitizers in catalytic hydrogen evolution from water in the presence of triethylamine as a sacrificial reducing agent. Applying an in situ formed iron-based water reduction catalyst derived from [HNEt(3)](+) [HFe(3)(CO)(11)](-) and tris[3,5-tris-(trifluoromethyl)-phenyl]phosphine as the ligand, [Ir(2-phenylbenz-oxazole)(2)-(bpy)]PF(6) proved to be the most efficient complex giving a quantum yield of 16% at 440 nm light irradiation.