title: Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers.
abstract: The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2''-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.
authors.affiliation: Istituto FRAE-CNR, Bologna, Italy.
authors.forename: Susana
authors.initials: S
authors.lastname: Encinas
authors.forename: Lucia
authors.initials: L
authors.lastname: Flamigni
authors.forename: Francesco
authors.initials: F
authors.lastname: Barigelletti
authors.forename: Edwin C
authors.initials: EC
authors.lastname: Constable
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Housecroft
authors.forename: Emma R
authors.initials: ER
authors.lastname: Schofield
authors.forename: Egbert
authors.initials: E
authors.lastname: Figgemeier
authors.forename: Dieter
authors.initials: D
authors.lastname: Fenske
authors.forename: Markus
authors.initials: M
authors.lastname: Neuburger
authors.forename: Johannes G
authors.initials: JG
authors.lastname: Vos
authors.forename: Margareta
authors.initials: M
authors.lastname: Zehnder