Synthesis and properties of tetrasubstituted 1,10-phenanthrolines and their ruthenium complexes

The synthesis and the photophysical properties of a series of tetrasubstituted phenanthroline (phen) ruthenium complexes of the type [Ru(tbbpy)(2)(phen-R-4)](2+) (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; phen = 1, 10-phenanthroline; R represents the substitution at 3-, 5-, 6- and 8-positions with phenyl, 4tert-butylphenyl and para-biphenyl) and of a homoleptic [Ru(phen-R'4)3]2, (R' = 4-tert-butylphenyl) are described. The phen-R4 ligands were obtained in high yields using Suzuki-type coupling reactions. The solid-state structure of 3,5,6,8-tetraphenylphenanthrohne is reported. The investigation of the photophysical properties of the free ligands reveals a pronounced effect of the aryl substitution on absorption and emission properties. These properties are mirrored in the corresponding complexes, which possess room-temperature emission lifetimes of up to 2833 ns.