GROUND-STATE AND EXCITED-STATE INTERACTIONS BETWEEN THE TRIS(2,2'-BIPYRIDINE)RUTHENIUM(2-SOLUTION() ION AND PHENOL IN AQUEOUS)

Although phenol (PhOH) does not quench Ru(bpy)(3)(2+) due to unfavora ble energetics, its presence in aqueous solution results in a blue shi ft in the emission spectrum and a change in the observed lifetime (tau (obs)) The effect of temperature (5-70 degrees C) and [PhOH] (0.1-0.7 M) on tau(obs) is complex; at low T, where nonradiative decay is the d ominant process, tau(obs) increases with increasing [PhOH]; at high T the opposite effect is seen, reflecting the dominance of the thermal p opulation of the d-d excited state. The NMR spectra of both Ru(bpy)(3 )(2+) and PhOH are altered in the presence of each other, indicating t he existence of ground-state interactions that are, undoubtedly, hydro phobic or pi-stacking in nature. The NOE difference spectra show that the H-3,H-5 protons of PhOH couple with the H-4,H-4 and H-6,H-6, proto ns of Ru(bpy)(3)(2+), indicating the existence of an offset face-to-fa ce orientation. (C) 1997 Elsevier Science S.A.