New ligands in the 2,2′-dipyridylamine series and their Rei complexes; synthesis, structures and luminescence properties

A series of new derivatives of the di2-pyridylamine ligand has been prepared, having the general formula py2NR, where R is one of a wide range of groups including naphthyl, pyrenyl, benzo-18-crown-6, pyrenyl, oxazolyl and bromo-biphenyl. All ligands are luminescent, with emission maxima between 370 and 520 nm, and with quantum yields in fluid solution of up to 0.74. Reaction of these ligands with ReCO5Cl afforded complexes of the type ReCO3ClL in which the di2-pyridylamine ligand binds as an N,N-bidentate chelate viathe two pyridyl units; five such complexes have been structurally characterised. With one exception the complexes are essentially non-luminescent, which we ascribe to the energetic availability of metal-based d-d excited states which can quench any MLCT or ligand-centred excited states. The exception is ReCO3Cltppd where tppd  N,N,N′,N′-tetrakis2-pyridyl-p-phenylenediamine in which one di2-pyridylamine site is occupied by a ReCO3Cl unit but the other is vacant; this luminesces in fluid solution at 516 nm   0.04, τ  42 ns.