Luminescence of Molecular and Block Copolymeric 2,7-Bis(phenylethenyl)-fluorenones; Identifying Green-Band Emitter Sites in a Fluorene-Based Luminophore

• Published in: Chemistry of materials Vol. 19; no. 13; pp. 3265 - 3270
• Main Authors: Rathnayake, Hemali P, Cirpan, Ali, Karasz, Frank E, Odoi, Michael Y, Hammer, Nathan I, Barnes, Michael D, Lahti, Paul M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26.06.2007
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm070552h

2,7-Bis(3,4,5-trimethoxyphenylethenyl)fluorenone (OFOPV) and a segmented oligomer analogue linking OFOPV units with polymethylene flexible spacersalt-poly(2,6-dimethoxylphenylene-4-vinylene-[9-fluorenone-2-yl-7-vinylene]3,5-dimethoxyphenylene-4-[1,6-hexanedioxyl]) (pFOPV)were synthesized and their luminescence properties studied. Solution-phase photoluminescence (PL) of OFOPV and pFOPV shows concentration-dependent relative intensities of a fine-structured higher energy band and a featureless lower energy band, consistent with solution excimer formation. Neat film PL and electroluminescence (EL) spectra using 100% OFOPV and pFOPV emitter layers show red emission bands (λmax ∼ 610 nm). Solid film PL spectra of OFOPV diluted in PMMA or Zeonex are significantly blue-shifted relative to the neat film spectra. PL and EL spectra of 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethylfluorene (OFPV) blended with <1% by weight of OFOPV gives significant green region (g-band) emission in addition to the normal blue emission of OFPV. Monomeric OFOPV produced by adventitious oxidation is therefore identified as giving g-band emission in thermally stressed OFPV-based OLEDs, due to intermolecular energy transfer from OFPV excitons to lower energy OFOPV. The red emission in neat solid-phase OFOPV and pFOPV appear to arise from fluorenone-type excimers that do not play a direct role in g-band emission in this case.