abstract
We report the solvent-driven assembly of a polyelectrolytic polyfluorene-polythiophene diblock copolymer-poly[9,9-bis(2-ethylhexyl)fluorene]-b-poly[3-(6-trimethylammoniumhexyl)thiophene] (PF2/6-b-P3TMAHT)-in tetrahydrofuran (THF), water, their 1:1 mixture and in subsequently prepared thin films, as investigated using a combination of scattering, microscopic and photoluminescence techniques. In solution PF2/6-b-P3TMAHT forms large (> 100 nm) aggregates which undergo a transition from objects with surface fractal interface (THF) to ones with a significant planar component due to the presence of the 2-dimensionally merged ribbon-like aggregates or fused walls of the observed vesicular aggregates [THF-water (1:1)]. In THF-water and water the blocks are loosely segregated into P3TMAHT and PF2/6 rich domains, with PF2/6 dominating the aggregate interior. Depending on solvent, the spun films contain either aggregates with a crystalline interior (THF) or large 200 nm-2 mu m vesicular aggregates embedded in a featureless matrix (THF-water and water). Structural variations are concomitant with distinctive solvatochromic changes in the photophysical properties including a color change from deep red (THF) to pale orange (THF-water and water) in solution, a decrease in fluorescence quantum yield with increasing water content, and a shift from photoluminescence of individual PF2/6 blocks (THF) to efficient PF2/6 -> P3TMAHT energy transfer (THF-water and water).
keywords
X-RAY-SCATTERING; CONJUGATED POLYMERS; SOLID-STATE; NANOSTRUCTURE FORMATION; THERMOTROPIC ALIGNMENT; MOLECULAR-WEIGHT; QUANTUM YIELDS; COPOLYMERS; FILMS; MORPHOLOGY
subject category
Chemistry; Materials Science
authors
Knaapila, M; Evans, RC; Gutacker, A; Garamus, VM; Torkkeli, M; Adamczyk, S; Forster, M; Scherf, U; Burrows, HD
Groups
acknowledgements
We thank A. P. Monkman of the University of Durham for many fruitful discussions and Y. Cerenius of MAX-lab as well as W. Caliebe and A. Timmann of HASYLAB for assistance. R.C.E thanks FCT for a postdoctoral fellowship (SFRH/BPD/42450/2007). U.S. acknowledges partial funding by the EC seventh Framework Programme collaborative project