105 Studies of the Upconversion of Green to Blue Light by Solutions of Ruthenium(II) Photosensitizers and 9,10-Diphenylanthracene as Emitter

Wednesday, November 4, 2009: 11:20 AM
Charolais (Camino Real Hotel)
Kullatat Suwatpipat , Department of Chemistry, Mississippi State University, Mississippi State, MS
Stephen C. Foster , Department of Chemistry, Mississippi State University, Mississippi State, MS
William P. Henry , Department of Chemistry, Mississippi State University, Mississippi State, MS
A solution of a ruthenium(II) complex and 9,10-diphenylanthracene (DPA) in dichloromethane was irradiated with a 514 nm laser. A green photon was absorbed by the ruthenium complex resulting in a triplet excited state. This species then transfers energy to a DPA molecule producing a triplet state excited DPA. Triplet-triplet annihilation between two excited DPA molecules generates singlet excited and ground state DPA molecules. The excited singlet DPA then emits a blue photon with wavelength between 415-500 nm to return to its ground state. Thus the upconversion of lower-energy light to higher-energy light occurs.     
       Three homoleptic ruthenium(II) complexes, [Ru(bpy)3](PF6)2 (bpy = 2,2’-bipyridine), [Ru(dmb)3](PF6)2 (dmb = 4,4’-dimethyl-2,2’-bipyridine) and [Ru(phen)3](PF6)2 (phen = 1,10-phenanthroline) were investigated as photosensitizers. In addition, six heteroleptic complexes were used in these studies: [Ru(bpy)2(dmb)](PF6)2, [Ru(bpy)(dmb)2](PF6)2, [Ru(bpy)2(phen)](PF6)2, [Ru(bpy)(phen)2](PF6)2, [Ru(dmb)2(phen)](PF6)2 and [Ru(dmb)(phen)2](PF6)2. The order of upconversion efficiency for the homoleptic complexes from highest to lowest was [Ru(dmb)3](PF6)2, [Ru(phen)3](PF6)2, [Ru(bpy)3](PF6)2, which agreed with their absorptivity at the 514 nm excitation wavelength. The heteroleptic complexes were inferior in upconversion efficiency to the homoleptic ones.     
       The results obtained for varying concentrations of both photosensitizer and emitter will be presented as will the effect of oxygen on the upconversion. Both laser power and positioning of the solution cell dramatically impact the upconversion intensity as will be described. This study confirms the general mechanism proposed earlier by other researchers and allows for further clarification of the chemical reactions that need to be considered when attempting to design upconversion systems.