Solution-Processible Conjugated Electrophosphorescent Polymers

Abstract

We report the synthesis and photophysical study of a series of solution-processible phosphorescent iridium complexes. These comprise bis-cyclometalated iridium units [Ir(ppy)(2)(acac)] or [Ir(btp)(2)(acac)] where ppy is 2-phenylpyridinato, btp is 2-(2'-benzo[b]thienyl)pyridinato, and acac is acetylacetonate. The iridium units are covalently attached to and in conjugation with oligo(9,9-dioctylfluorenyl-2,7-diyl) [(FO)(n)] to form complexes [Ir(ppy-(FO)(n))(2)(acac)] or [Ir(btp-(FO)(n))(2)(acac)], where the number of fluorene units, n, is 1, 2, 3, approximately 10, approximately 20, approximately 30, or approximately 40. All the complexes exhibit emission from a mixed triplet state in both photoluminescence and electroluminescence, with efficient quenching of the fluorene singlet emission. Short-chain complexes, 11-13, [Ir(ppy-(FO)(n)-FH)(2)(acac)] where n = 0, 1, or 2, show green light emission, red-shifted through the FO attachment by about 70 meV, but for longer chains there is quenching because of the lower energy triplet state associated with polyfluorene. In contrast, polymer complexes 18-21 [Ir(btp-(FO)(n))(2)(acac)] where n is 5-40 have better triplet energy level matching and can be used to provide efficient red phosphorescent polymer light-emitting diodes, with a red shift due to the fluorene attachment of about 50 meV. We contrast this small (50-70 meV) and short-range modification of the triplet energies through extended conjugation, with the much more substantial evolution of the pi-pi* singlet transitions, which saturate at about n = 10. These covalently bound materials show improvements in efficiency over simple blends and will form the basis of future investigations into energy-transfer processes occurring in light-emitting diodes.

Design and Synthesis of Phosphorescent Iridium Containing Dendrimers for Potential Applications in Organic Light‐Emitting Diodes

“…As reported earlier in literature, [20] we also find that this synthesis is a better approach than the direct chelation of phenylpyridine containing oligomers with IrCl 3 . All of the intermediate compounds were characterized by 1 H NMR.…”

“…In addition, a much weaker and lower energy absorption band was also found well extending into the visible region (between 420-500 nm), which probably correspond to an admixture of metal to ligand charge transfers ( 1 MLCT and 3 MLCT), and a 3 pp à transition. [20] Compared with widely used Ir(PPy) 3 , the intensity of the MLCT transitions of these three Ir-containing dendrimers was very low, simply because of the low loading of iridium complex in the materials. A similar phenomenon has been observed by Holmes et al in Ir-containing oligofluorenes.…”

“…The absolute PL quantum yields of the thin films were measured at ambient temperature using a commercial fluorimeter in combination with an integrating sphere according to the literature procedure. [17] The starting materials, 2 0 ,7-bis(9,9-dioctylfluorene)-2-boronic acids, [18] 3,6-dibromocarbazole, [19] N-octyl-3,6-dibromocarbazole, [19] and Ir(Br-ppy) 2 (acac) [20] (Br-ppy ¼ 2-(4-bromophenyl)pyridine, acac ¼ acetyl acetonate) were prepared using the procedures reported previously.…”

“…The development of solutionprocessible phosphorescent materials has become the focus of intense researches in this field. [20][21][22][23] Given that carbazole-based materials are widely used as hosts for triplet emitters in OLEDs, it is not surprising that a variety of carbazole oligomers have been attached to iridium complexes. [10,12,24] In this study, we designed and synthesized two branched carbazole oligomers and then attached them to a core iridium complex by Suzuki coupling.…”

Polymer‐Fullerene Bulk‐Heterojunction Solar Cells

“…[82][83][84][85] The metal atom integrated into the polymer backbone can increase the mixing of the first excited singlet and triplet states, leading to higher electroluminescence quantum efficiencies of PLEDs. In contrast, metallated conjugated polymers have rarely been tested as donor materials in bulk-heterojunction solar cells.…”