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A series of soluble alternating polyfluorene copolymers with different main chain structures and those of the same main chain structure polyfluorene-co-alt-phenylene with different functional groups attached at the 2- and/or 5-positions of the phenylene ring were synthesized by a palladium-catalyzed Suzuki coupling reaction. All 10 polymers had the band gaps ranging from 2.81 to 3.35 eV, corresponding to blue-light emission. Through controllable modification for both the main chain structures and the side chains, not only the optical and electronic properties of the blue emissive polymers had been tuned, but also the structure−property relationships, especially the HOMO and LUMO energy level engineering, had been studied. Relatively high PL efficiency in both solution and film states, good thermal stability, and relatively high glass transition temperatures were demonstrated on these polymers. In general, polymers with the main chain structure of polyfluorene-co-alt-phenylene were found to have higher Φfl both in solution and in solid states than those copolymers with other main chain structures. For the polymers with the same main chain structure of polyfluorene-co-alt-phenylene, attachment of electron-donating alkoxy groups on phenylene ring (P4) had caused a spectral red shift, corresponding to slightly decreased HOMO and increased LUMO energy levels, while attachment of electron-withdrawing ester groups (P6) had led to an obvious blue shift in the absorption spectrum with a decrement in both the HOMO and LUMO energy levels as compared to that of the unsubstituted polymer (P2). As for the polymers of different main chain structures, in comparison with the homopolymer P1, carbazole comonomer had caused an obvious spectral blue shift with increased HOMO and decreased LUMO energy levels. A decrement in both the HOMO and LUMO energy levels had been observed for P9 in which naphthalene was chosen as the comonomer. However, for P10, although there was no obvious difference between the absorption and emission spectra of P10 as compared to those of P1, both the HOMO and LUMO energy levels were reduced greatly when they were compared with those of P1.

NotesbondingSg Potassium acetate, which provides a strong hydrogen-bonding anion, also shows some promoting effect in this reaction. The absence of 3 in product solutions suggests its formation is rate limiting. However, the use of KBr in place of :KF gives both p-BrC6H4CF3 and 2.The convers,ion of 2 t o 4 likely occurs by a mechanism involving ammonolysis of the CF3 substituent to give p -H2NC6H4CF2NHz. Subsequent elimination of HF would generate 4.' O Experimental SectionMaterials. All reagents were commercially available and used without further purification. Anhydrous KF was handled under N2 to prevent deliquescence. Precautions were taken to prevent oxidation of cuprous chloride.Ammonolysis of p-Chlorobenzotrifluoride. Two procedures were used for the ammonolysis reactions. For the first procedure, an 80--mL Hast.elloy shaker tube was charged with reactants, catalysts, and promot.ers. The tube was chilled to -80 OC, evacuated, and, if desired, additional gas added prior to heating for a specified time. After reaction, the tube contents were removed and analyzed by GC or GC/mass spectrometry. The second, and most frequently used, procedure is similar to that described by Cramer." The reaction components were charged by weight to matched glass tubes (internal volume of 4.8-6.0 mL). Ammonia was condensed into the chilled, evacuated tubes, using standard vacuum line .techniques, and the tubes were sealed. A 4 W m L autoclave was charged with the tubes (usually five) with ethanol (as the heat transfer fluid) and N2 (for external pressure) and heated with agitation for the specified time.After reaction, the glass tubes were chilled, opened, and stoppered with a rubber septum containing a hollow needle through which the ammonia distilled as the tubes warmed to room temperature. The tube contents were then quantitatively transferred to 25-mL vodumetric flasks with carrier solution (79.7% cyclopentane, 20% chloroform, and 0.3 70 morpholine) for analysis by high-pressure liquid chromatography, high-pressure LC. Alternatively, the reactions were run with 1% n-undecane as internal standard for GC analysis. Experimental results are summarized in Table II.12 Hydrolysis of p-Aminobenzotrifluoride (2). A mixture of 4.0 mL of 2,0.3 g each !of copper powder and Cu2C12, 1.5 g of CaO, and 28 mL of 28% aqueous ammonia was heated for 2 h a t 240 "C. Analysis by GC of' the resulting solution showed that 2 had been completely consumed. No fluorine-containing components

Three conjugated polymers comprised of 9,9-dioctylfluorene and 2,2‘-bipyridine, which are alternatively linked by the C−C single bond (P1), vinylene bond (P2), or ethynylene bond (P3), have been synthesized via the Suzuki reaction, the Wittig−Horner reaction, and the Heck reaction, respectively. The optical, electrochemical, and other physical properties of the polymers are dependent on the linkers. The polymer linked by the C−C single bond exhibits a much larger Stokes shift compared with the other two polymers, indicative of higher extended and rigid backbone conformations in the polymers linked by the vinylene and ethynylene bonds. All the three polymers are sensitive to the existence of a variety of transition metal ions due to the chelation between the 2,2‘-bipyridyl moieties and the metal ions. For the metal ions which have moderate and weak coordination ability with the 2,2‘-bipyridyl moieties, an obvious difference in response sensitivity is observed among the three polymers:  P1 has the highest sensitivity, which is followed by P2, and P3 always exhibits the lowest sensitivity. The different sensing sensitivity is attributed to the different backbone rigidity of the three polymers, which is caused by the three different linkers. The results suggest the use of C−C single bond linker in the molecular design toward the 2,2‘-bipyridyl-based conjugated polymer chemosensors for achieving higher sensing sensitivity.