A new class of functionalized terpyridyl ligands as building blocks for photosensitized supramolecular architectures.: Synthesis, structural, and electronic characterizations

A new class of triarylpyridinio-derivatized [4'-(p-phenyl)(n)]terpyridyl ligands (R2RTP+)-R-1-T-2-(p)(n)tpy, was designed as a novel category of electron-acceptor (A)-substituted proto-photosensitizing molecules. The first elements of this versatile family of ligands (i.e., n = 0, 1 and R-1 = R-2 = H), H3TP+-tpy and H3TP+-ptpy, were synthesized as well as their Ru(II) and Os(II) complexes to form the related acceptor-functionalized M(tPY)(2)(2+) and M(PtPY)(2)(2+) pholosensitizer components denoted PO and P1, respectively. Within the P1 series of compounds, an electron-donor (D)-substituted ligand, Me2N-ptpy, was also involved and associated with H3TP+-ptpy, giving rise to various combinations (up to 10 polyad systems). The two resulting series of nanometer-scale rigid rod-like photosensitized supramolecular architectures are of potential interest for long-range photoinduced electron transfer purposes. The main structural features of such supermolecules were determined by comparing the results obtained from (i) single-crystal X-ray analysis of the two free ligands together with that of the P0A/Ru and P1A(2)/Ru complexes and (ii) a detailed solution H-1 NMR study of the PO series and, more specifically, of the P0A/Ru dyad (ROESY experiment), It is shown that the pseudoperpendicular conformation of the covalently linked A and P subunits found in the solid state is persistent in fluid medium; i.e., A is not conjugated with P (PO and P1). The first insights regarding the consequences upon intercomponent couplings of combined substituent effects and conjugation (case of D-based polyads)-or absence of conjugation-are discussed in the light of ground-state electronic properties of the compounds.