Interactions between polymer chains of poly(9,9-dioctylfluorene-2,7-diyl) (PF8) have been studied in toluene solution over a wide concentration range using multinuclear NMR spectral and relaxation measurements with both the fully protonated and alkyl chain deuterated polymers, small angle neutron scattering (SANS), together with theoretical calculations using DFT and semiempirical methodologies. Full assignment of the 1H and 13C chemical shifts in the NMR spectra of isolated chains of PF8 has been made using DFT, and are in good agreement with spectra in chloroform and in toluene solutions. Somewhat different behavior is seen in toluene solution, where, upon increasing polymer concentration, broadening of the alkyl chain resonances is seen, consistent with interactions between the side chains. Similar behavior is seen with the 2H resonance of PF8-d 34. In both cases, line-narrowing and restoration of the structured alkyl chain resonances is seen upon studying the spectra of concentrated solutions using the magic angle spinning (MAS) technique, in agreement with the attribution of the broadening to interchain interactions between the octyl groups. Support for this interpretation comes from 1H and 13C spin−lattice relaxation time measurements, which also show differences in group dynamics along the alkyl chains. Semiempirical theoretical calculations, using PM3 and PM6 Hamiltonians, add further support to the importance of interactions between the alkyl groups of separate PF8 chains. SANS measurements on PF8 in toluene solutions from very dilute to concentrated solutions, extended to ultrasmall q ranges, provide further insight. Three concentration ranges can be identified. In dilute solutions, the results suggest that PF8 is present as fully dissolved polymer coils. Upon increasing polymer concentration, an intermediate region is observed, in which there are indications of transient contacts between the polymers, which the NMR results suggest involves side chain interactions. As a consequence of interactions between the chains, gel formation occurs. On the basis of these and previous results, some general considerations are presented upon the solubility and aggregation behavior of PF8, including indications of how interactions between alkyl chains may be important in the stabilization of the so-called β-phase of PF8.

A new water soluble fluorene‐based polyelectrolyte containing on‐chain porphyrin units has been synthesized via Suzuki coupling, for use in optoelectronic devices. The material consist of a random copolymer of poly{1,4‐phenylene‐[9,9‐bis(4‐phenoxy butylsulfonate)]fluorene‐2,7‐diyl} (PBS‐PFP) and a 5,15‐diphenylporphyrin (DPP). The energy transfer process between the PBS‐PFP units and the porphyrin has been investigated through steady state and time‐resolved measurements. The copolymer PBS‐PFP‐DPP displays two different emissions one located in the blue region of the spectra, corresponding to the fluorene part and another in the red due to fluorescent DPP units either formed directly or by exciton transfer. However, relatively inefficient energy transfer from the PFP to the on‐chain porphyrin units was observed. We compare this with a system involving an anionic blue light‐emitting donor PBS‐PFP and a anionic red light‐emitting energy acceptor meso‐tetrakisphenylporphyrinsulfonate (TPPS), self‐assembled by electrostatic attraction induced by Ca2+. Based on previous studies related to chain aggregation of the anionic copolymer PBS‐PFP, two different solvent media were chosen to further explore the possibilities of the self‐assembled system: dioxane–water and aqueous nonionic surfactant n‐dodecylpentaoxyethylene glycol ether (C12E5). In contrast, with the on‐chain PBS‐PFP‐DPP system the strong overlap of the 0‐0 emission peak of the PBS‐PFP and the Soret absorption band of the TPPS results in an efficient Förster transfer. This is strongly dependent on the solvent medium used. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

An anionic fluorene-phenylene poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}-based copolymer containing on-chain perylenediimine (PDI) chromophoric units, PBS-PFP-PDI, was synthesized and its photophysical properties studied as aggregates and isolated chains in water and dioxane/water (1:1) solution. UV-vis and emission spectroscopy measurements, time-correlated single photon counting, and wide field imaging have been employed to investigate the excited-state behavior of the PBS-PFP-PDI copolymer, including the effect of environment on the energy and electron transfer to the on-chain PDI chromophore. Although the Förster overlap integral is favorable, no evidence is found for intramolecular singlet excitation energy transfer in isolated copolymer chains in solution. Fluorescence is suggested to involve an interchain process, thus revealing that isolated copolymer chains in solution do not undergo efficient intramolecular energy transfer. However, quenching of the PBS-PFP excited state by PDI is observed in aqueous media and ultrafast pump-probe studies in water or dioxane-water solutions show that electron transfer occurs from the phenylene-fluorene units to the PDI. The extent of electron transfer increases with aggregation, suggesting it is largely an interchain process. The interaction of the negatively charged PBS-PFP-PDI copolymer with the positively charged surfactant hexadecyltrimethylammonium bromide (CTAB) in solution has also been studied. The copolymer PBS-PFP-PDI aggregates with the surfactant already at concentrations below the critical micelle concentration (cmc) and the nonpolar environment allows intermolecular energy transfer, observed by the weak emission band located at 630 nm that is associated with the emission of the PDI chromophore. However, the fact that the PDI photoluminescence (PL) lifetime (~1.4 ns) obtained in the presence of CTAB is considerably shorter than that of the nonaggregated chromophore (~5.4 ns) suggests that even in this case there is considerable PL quenching, possibly through some charge transfer route. The increase of the PBS-PFP-PDI photoluminescence intensity at surfactant concentrations above the cmc indicates deaggregation of polyelectrolyte within the initially formed polyelectrolyte-surfactant aggregates.