Synthesis of Ru(II) polypyridyl complexes containing perylene-diimide ligands: spectroscopic and electrochemical properties

Abstract

Photoinduced charge separation (CS) excited states are essential processes that occur in nature through the absorption of visible light by chlorophyll in the photosynthetic system generating molecular oxygen and glucose for plants. Due to the importance and scope of applications of these processes, several research groups have been dedicated to the synthesis of artificial molecules such as dyads or supramolecular systems that present excited states of CS. Among the various systems studied, perylene-diimide molecules (PDIs) are extensively explored due to their optical properties, thermal and photochemical stability. One of the difficulties in studies with PDIs is the fact that they are insoluble in most solvents and PDI molecules are prone to form aggregates via À-À interactions, which lead to fluorescence quenching. In order to minimize these effects and obtain a CS state, we have recently prepared ruthenium-perylene dyads, namely cis-[(phen)2Ru(pPDIp)]2+, where pPDIp is a perylene functionalized at the imide positions with coordinating 1,10-phenanthroline (phen). The prepared dyads present solubility in organic solvents and are relatively soluble in an aqueous medium, their photochemical and photophysical properties are attributed to the {Ru(phen)3}2+ and pPDIp moieties, in addition to presenting the CS intermediate state observed by time-resolved absorption techniques that decays for generate the triplet excited states of the pPDIp with lifetime of 1.8 µs and the energy transfer Æ1Ÿ2 = 0.54, which favored the studies of electron transfer and photoinduced intermolecular energy. In order to evaluate the influence and effect of electron donating groups attached to polypyridyl ligands coordinated to Ru(II) on the spectroscopic and electrochemical properties of these dyads, in this project we intend to synthesize and characterize the complexes [Ru(±-diimina)2(pPDIp)](PF6)2 where ±-diimina = 5,6-Dimethyl-1,10-phenanthroline, 2,2'-Bipyridine and 4,4'-Dimethyl-2,2'-bipyridine. We intend to relate the spectroscopic (UV-Vis and luminescence) and electrochemical (cyclic voltammetry) properties of these new complexes and investigate the effect of the substituents on the generation of CS states. This study may contribute to deepening knowledge about coordination chemistry, UV-vis electronic spectroscopy, luminescence and in electrochemical techniques as well as open new research fronts for the practical application of these compounds.