title: Photophysics of pi-conjugated metal-organic oligomers: aryleneethynylenes that contain the (bpy)Re(CO)(3)Cl chromophore.
abstract: A comprehensive study of a series of four monodisperse, metal-organic pi-conjugated oligomers of varying length is reported. The oligomers are based on the aryleneethynylene architecture, and they contain a 2,2'-bipyridine-5,5'-diyl (bpy) metal binding unit. The photophysical properties of the free oligomers and their complexes with the (L)Re(I)(CO)(3)X chromophore (where L = the bpy-oligomer and X = Cl or NCCH(3)) were explored by a variety of methods including electrochemistry, UV-visible absorption, variable temperature photoluminescence (PL), transient absorption (TA), and time-resolved electron paramagnetic spectroscopy (TREPR). The absorption of the free oligomers and the metal complexes is dominated by the pi,pi* transitions of the pi-conjugated oligomers. The free oligomers feature a strong blue fluorescence that is quenched entirely in the (L)Re(I)(CO)(3)X complexes. The metal-oligomers feature a weak, relatively long-lived red photoluminescence that is assigned to emission from both the (3)pi,pi* manifold of the pi-conjugated system and the dpi Re --> pi* bpy-oligomer metal-to-ligand charge transfer ((3)MLCT) state. On the basis of a detailed analysis of the PL, TA, and TREPR results an excited-state model is developed which indicates that the oligomer-based (3)pi,pi* state and the (3)MLCT states are in close energetic proximity. Consequently the photophysical properties reflect a composite of the properties of the two excited-state manifolds.
authors.affiliation: Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611-7200, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Walters
authors.forename: K D
authors.initials: KD
authors.lastname: Ley
authors.forename: C S
authors.initials: CS
authors.lastname: Cavalaheiro
authors.forename: S E
authors.initials: SE
authors.lastname: Miller
authors.forename: D
authors.initials: D
authors.lastname: Gosztola
authors.forename: M R
authors.initials: MR
authors.lastname: Wasielewski
authors.forename: A P
authors.initials: AP
authors.lastname: Bussandri
authors.forename: H
authors.initials: H
authors.lastname: van Willigen
authors.forename: K S
authors.initials: KS
authors.lastname: Schanze