Luminescent Properties of Bis(n5-pentamethyl-cyclopentadienyl)ytterbium Derivatives

Several adducts of (n5-Me5C5)2Yb(II) (1) and (n5-Me5C5)2 YbCl(III) (2) have been found to exhibit photoluminescence (PL) at 295K. The mono-THF adducts of 1 and 2 have served as the parent complexes for this study;1,2,3 they are orange-red (λmax ~ 445, 505 and 790 nm)4 and purple (λmax ~ 520 nm), respectively. Electronic spectra of the adducts are sensitive to the Lewis base coordinated to the Yb(II) or Yb(III) center. Excitation into any of the visible absorption bands of 1 at 295K in toluene yields a broad (FWHM ~100 nm) PL band with uncorrected λmax ~935 nm. Solutions of 1 in THF, compositionally dominated by the bis-THF adduct, exhibit a band of similar character, but possessing, in addition, a shoulder at ~900 nm. Solid-state PL spectra of the mono- and bis-THF adducts of 1 display band maxima at ~960 and 910 nm, suggesting that the shoulder observed in THF solution is due to the bis-THF adduct. The THF data suggest that excited-state adduct dissociation competes favorably with other decay routes of the bis-THF adduct. Other adducts studied by dissolving 1·THF in the corresponding solvent include Et20, for which PL at 875 nm is found, and CH3CN and pyridine, for which no PL between ~700-1000 nm is observed. In THF, 2 exhibits the sharp PL bands characteristic of f-f transitions between ~950-1000 nm; spectra are compared to those previously observed for adducts of (n5-C5H5)3 Yb(III).5