The Role of Isomeric Effects on the Luminescence Lifetimes and Electrochemistry of Oligothienyl‐Bridged Dinuclear Tris(2,2′‐bipyridine)ruthenium(II) Complexes

Abstract

The luminescence lifetimes (in CH 3 CN at room temperature) and electrochemical potentials (in CH 3 CN) of a range of mono-and bis(bidentate) 2,2Ј-bipyridine-capped oligothiophene-bridged Ru II complexes based on the 6-(2-thienyl)-2,2Ј-bipyridine and 4-(2-thienyl)-2,2Ј-bipyridine motifs have been measured. The redox potentials occurred in a very narrow range and showed only small shifts from that of [Ru(bpy) 3 ] 2+ , which indicates that the inductive effects of the substituents on the 2,2Ј-bipyridine ligands are very similar across this series. In the complexes that incorporated a bithiophene moiety the oxidation of the bithienyl group occurred at higher potentials than the metal-centered Ru

The Effects of Pendant vs. Fused Thiophene Attachment upon the Luminescence Lifetimes and Electrochemistry of Tris(2,2′‐bipyridine)ruthenium(II) Complexes

“…As observed in our previous study,5 the red [Ru(bpy) 3 ] 2+ ‐type MLCT luminescence was quenched in those cases where a thiophenyl substituent was present in the 6‐position of the unique 2,2′‐bipyridine, the only exception being the prototype C1 and C3 where a very weak red luminescence was observed (see Table 2). Whereas, when the thiophene is attached to the 4‐position ( C2 ), a red luminescence and an excitation spectrum very similar to that of [Ru(bpy) 3 ] 2+ (Figure 4) are observed, although with a slightly greater quantum yield and longer lifetime (3000 ns) when compared to that of [Ru(bpy) 3 ] 2+ (1745 ns) obtained under identical conditions.…”

“…The fusion of the thiophene ring onto the c face does not introduce the same steric strain to the inner coordination sphere, resulting in less positive Ru III /Ru II couples and longer luminescence lifetimes (see next section). In our earlier work,5 a second oxidation process at higher potentials was detected in the voltammograms of complexes bearing a bithiophenyl moiety attached to one of the bpy ligands, whereas those possessing only a single (uncoupled) thiophene ring possessed no such wave. As anticipated, no such oxidation processes were observed for the complexes C1 – C13 within the solvent limit.…”

“…Those complexes which contained a fused thiophene on the c face ( C12 and C13 ) displayed the longest lifetimes in this series, in line with the fact that their coordination geometries most closely mimic that of [Ru(bpy) 3 ] 2+ . As only weak electronic coupling was found in bridged dimetallic complexes comprising the chelating motifs L1 and L2 ,5 it is therefore of interest to extend these studies through the generation of bridged complexes by utilising the fused L12 and L13 motifs. The study of the photophysical properties and intervalence charge‐transfer properties (IVCT) of such bridged complexes will help elucidate the optimal structural and electronic requirements for communication between metal centres linked in this manner.…”

“…The coupling between an energy/electron source and its conducting unit is of great importance 4. In our previous study5 we examined the isomeric effects within the covalent coupling of oligothiophene units and 2,2′‐bipyridine chelating units upon the electrochemical and photophysical properties of their [Ru(bpy) 2 L] 2+ complexes. It was found that coupling of the oligothiophene in the 6‐position of the 2,2′‐bipyridine unit led to quenching of all long‐lived red luminescence This is due to the energy of the metal‐centredd–d transition being lowered for 6‐substituted bipyridines, leading to competitive radiationless relaxation and quenching of the luminescence.…”

The intramolecular aryl embrace: from light emission to light absorption

“…Compound 2 was obtained as a brown oil as the 1st major fraction, and after recrystallization from hexanes, 2 was isolated as white crystals (220 mg, 10%). The 2nd major fraction was identified as 4-(thiophen-2-yl)-2,2¢-bipyridine 35 (260 mg, 12%). Spectroscopic data for 2 were in agreement with those published.…”