Surface-confined Ullmann coupling of thiophene substituted porphyrins.

The covalent coupling of (5,10,15,20-tetrabromothien-2-ylporphyrinato)zinc(II) (TBrThP) molecules on the Ag(111) surface has been investigated under ultra-high-vacuum conditions, using scanning tunnelling microscopy and x-ray photoelectron spectroscopy. The findings provide atomic-level insight into surface-confined Ullmann coupling of thiophene substituted porphyrins, analyzing the progression of organometallic intermediate to final coupled state. Adsorption of the TBrThP molecules on the Ag(111) surface at room temperature is found to result in the reductive dehalogenation of the bromothienyl substituents and the subsequent formation of single strand and crosslinked coordination networks. The coordinated substrate atoms bridge the proximal thienyl groups of the organometallic intermediate, while the cleaved bromine atoms are bound on the adjacent Ag(111) surface. The intermediate complex displays a thermal lability at ∼423 K that results in the dissociation of the proximal thienyl groups with the concomitant loss of the surface bound bromine. At the thermally induced dissociation of the intermediate complex the resultant thienylporphyrin derivatives covalently couple, leading to the formation of a polymeric network of thiophene linked and meso-meso fused porphyrins.

Reinvestigating 2,5-di(pyridin-2-yl)pyrazine ruthenium complexes: selective deuteration and Raman spectroscopy as tools to probe ground and excited-state electronic structure in homo- and heterobimetallic complexes.

The mono- (1) and dinuclear (2) ruthenium(II) bis(2,2'-bipyridine) complexes of 2,5-di(pyridin-2-yl)pyrazine (2,5-dpp), for which the UV/Vis absorption and emission as well as electrochemical properties have been described earlier, are reinvestigated here by resonance, surface enhanced and transient resonance Raman spectroscopy together with selective deuteration to determine the location of the lowest lying excited metal to ligand charge transfer ((3)MLCT) states. The ground state absorption spectrum of both the mono- and dinuclear complexes are characterised by resonance Raman spectroscopy. The effect of deuteration on emission lifetimes together with the absence of characteristic bipy anion radical modes in the transient Raman spectra for both the mono- and dinuclear complexes bridged by the 2,5-dpp ligand confirms that the excited state is 2,5-dpp based; however DFT calculations and the effect of deuteration on emission lifetimes indicate that the bipy based MLCT states contribute to excited state deactivation. Resonance Raman and surface enhanced Raman spectroscopic (SERS) data for 1 and 2 are compared with that of the heterobimetallic complexes [Ru(bipy)(2)(2,5-dpp)PdCl(2)](2+)3 and [Ru(bipy)(2)(2,5-dpp)PtCl(2)](2+)4. The SERS data for 1 indicates that a heterobimetallic Ru-Au complex forms in situ upon addition of 1 to a gold colloid.