SYNTHESIS AND PHOTOPHYSICAL PROPERTIES OF MONO(2,2',2''TERPYRIDINE) COMPLEXES OF RUTHENIUM(II)

A series of [Ru(tpy)(X)(Y)(Z)](n+) complexes have been synthesized (tpy = 2,2',2 ''-terpyridine: X = triphenylphosphine (PPh(3)); trans Y = Z = trifluoroacetate (CF3CO2-), n = 0 (1); trans Y = Z = 4-ethylpyridine (4-Etpy), n = 2(2): trans Y = Z = 4-(dimethylamino)pyridine (DMAP), n = 2 (3); Y = 4-Etpy, Z = chloride (Cl-), n 1 (4); cis Y = Z = 4-Etpy, n = 2 (5); X = Cl-; trans Y = Z = 4-Etpy, n. 1(6); X = Y = Z = 4-Etpy, n = 2 (7)) and isolated as their PF6- salts. UV-visible spectroscopic and electrochemical studies have been conducted and photochemical and photophysical properties of representative examples determined. Emission, absorption, and electrochemical properties depend on the nonchromophoric ligands and the coordination geometry. The complexes investigated emit in 4:1 (v/v) EtOH/MeOH glasses at 77 K and have lifetimes which range from 1.1 to 11.0 mu s depending on the ancillary ligands. Through a combination of emission spectral fitting and resonance Raman measurements on [Ru(tpy)2](PF6)(2), the acceptor characteristics of tpy as a chromophoric ligand have been analyzed. At room temperature the Ru(II) mono-tpy complexes are short-lived, weak emitters. Emission quantum yields and lifetimes for [Ru(tpy)(4-Etpy)(3)](PF6)(2) (7) and [Ru(tpY)(2)](PF6)(2) in 4:1 (v/v) EtOH/MeOH are strongly temperature dependent from T = 90-270 K. These results are consistent with the existence of low-lying dd states which are responsible for the short excited state lifetimes at room temperature and the appearance of ligand-loss photochemistry for 7.