ABSTRACT
A series of novel fused 4'-substituted 2,2' : 6',2''-terpyridine ligands and their ruthenium(II) complexes were prepared. The unusual 4'-substituents comprised 2,3,4,5-pentaphenylbenzene and its tert-butyl derivative (1 and 2) and the products from oxidative cyclodehydrogenation, i.e. polyaromatic fragments consisting of ten or thirteen fused benzene rings (3 and 4). The syntheses of all the ligands are discussed in terms of the demands and limitations of the Scholl reaction. The optical properties of the ligands, along with the single-crystal X-ray structures of 1 and 2, are presented. The latter show that the pentaphenylbenzene and terpyridine appendages of 1 and 2 are perpendicular in the solid state. Despite the inclusion of the large organic chromophore the absorption and emission properties of the Ru(II) bis-terpy complexes (of ligands 1, 2 and 3) were found to be comparable to those of [Ru(terpy)(2)](2+). They are non-emissive at room temperature but emit at 77 K with excited state lifetimes of 11-12 µs.
ABSTRACT
Two superaromatic terpyridine ligands (1 and 2) incorporating a hexa-peri-hexabenzocoronene (HBC) unit at the 4'-position have been prepared. In 1, the terpyridine and the HBC domains are directly fused, while in 2, they are separated by an acetylene linker. Also presented is the synthesis and characterization of several novel HBC derivatives, including 2-iodo-5,8,11,14,17-penta-tert-butylhexa-peri-hexabenzocoronene (7), a valuable synthetic intermediate. Different synthetic routes to 1 and 2 are employed, and two alternative methods resulted in excellent yields of 2. The optical properties of both novel terpyridines are examined using UV-visible absorption and emission spectroscopy. The single-crystal X-ray structures of 7 and a precursor, 4-iodo-4'-tert-butylphenylacetylene (5), are discussed.
ABSTRACT
Metal complexes [M(phtpy)(pztpy)](PF(6))(2) (phtpy = 4'-phenyl-2,2':6',2''-terpyridine, pztpy = 4'-(N-piperazinyl)-2,2':6',2''-terpyridine, M = Ru, Os) were prepared and examined spectroscopically and electrochemically. The piperazine attachment was found to significantly modify the photophysical and electrochemical properties compared to the parent bis-terpyridine complexes, causing a red-shift of the (1)MLCT (23 nm, 53.9 eV) and a substantial cathodic shift of the redox potential (0.3 V for Ru, 0.23 V for Os). Self-assembled monolayers (SAMs) of the complexes on polished gold electrodes were generated simply by the in situ formation of a dithiocarbamate (DTC) anchoring group at the terminal piperazinyl nitrogen on the pztpy ligand. Cyclic voltammetry revealed that the monolayers show excellent reversible behaviour and exceptional stability. The high stability of the SAMs is attributed to the strong bidentate attachment to the gold surface of the DTC tether and the favourable low oxidation potentials of the complexes which result from the electron-rich piperazine nitrogen on the pztpy ligand. Such DTC-based SAMs demonstrate a substantial improvement over commonly-employed thiol-based systems, and offer new scope for future development.
