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 (tp y = 2,2',2 ''-terpyridine: X = triphenylphosphine (PPh(3)); trans Y = Z = trifluoroacetate (CF3CO2-), n = 0 (1); trans Y = Z = 4-ethylpyridi ne (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-Etp y, n = 2 (5); X = Cl-; trans Y = Z = 4-Etpy, n. 1(6); X = Y = Z = 4-Et py, n = 2 (7)) and isolated as their PF6- salts. UV-visible spectrosco pic and electrochemical studies have been conducted and photochemical and photophysical properties of representative examples determined. Em ission, absorption, and electrochemical properties depend on the nonch romophoric ligands and the coordination geometry. The complexes invest igated 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 t py as a chromophoric ligand have been analyzed. At room temperature th e Ru(II) mono-tpy complexes are short-lived, weak emitters. Emission q uantum 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 de pendent from T = 90-270 K. These results are consistent with the exist ence of low-lying dd states which are responsible for the short excite d state lifetimes at room temperature and the appearance of ligand-los s photochemistry for 7.