Electrically conducting and thermally stable π-conjugated poly(arylene)s prepared by organometallic processes

Polyfluorenes with polyphenylene dendron side chains: toward non-aggregating, light-emitting polymers

A polyfluorene 12 has been prepared in which bulky polyphenylene dendrimer substituents suppress formation of long wavelength emitting aggregates, thus giving a polymer with pure blue emission. Absorption- and emission spectra and molecular modeling confirm that the bulky dendrimer side chains do not cause extra torsion between the fluorene units. New polyfluorenes with 9,9-diaryl substituents have been prepared to determine the minimum size of substituent necessary for aggregation suppression. An LED using 12 has been demonstrated to produce blue emission with onset voltages below 4 V.

Excimer Formation in Oligo[2,5-bis(hexadecyloxy)-1,4-phenylene]s Followed by Fluorescence Spectroscopy

Using the steady-state and time-resolved fluorescence spectroscopy, the behavior of "hairy-rod" oligo- and poly[2,5-bis(hexadecyloxy)-1,4-phenylene]s in tetrahydrofuran solutions was investigated. The materials were prepared by the Yamamoto coupling reaction using zinc as a reducing metal, the nickel(II)/triphenylphosphine complex as a catalyst, and 2,2'-bipyridine as a coligand. The appropriate oligomer fractions were separated by fractional precipitation and characterized by GPC and end group analysis. The fluorescence quantum yield of oligomers and polymers increased with their increasing conjugation length. The fluorescence emission spectra of polymers and longer oligomers exhibited one emission maximum at 390 nm with a single-exponential decay and fluorescence lifetimes (τ) around 1 ns. The substitution in positions 2 and 5 forces the adjacent backbone benzene units out of the plane, which results in twist angles 60-80°, and the bulky substituents exclude the cofacial sandwich-type configuration necessary for excimer formation. However, with shorter oligomers, another emission band at 460 nm appeared. Fluorescence decays at 460 nm were found to be double-exponential with longer excited-state lifetimes [e.g. τ1 = 6.9 ns (76%), τ2 = 2.4 ns (24%)]. With shorter oligomers (dimer, trimer), we assume a sandwich-type configuration with sufficiently close interchain distance and hence the excimer can form. Hydrophobic interactions of long aliphatic side chains in a polar medium play an important role in the excimer formation.

Unusual solvent effects on chiroptical properties of an optically active regioregular polythiophene in solution

The chiroptical properties of a novel, optically active regioregular poly[3-(4-((R)-4-ethyl-2-oxazolin-2-yl)phenyl)thiophene] (poly-1) were investigated in mixtures of a good solvent, chloroform, and a variety of poor solvents using CD spectroscopy. Most poor solvents induced CD on poly-1 with similar Cotton effects, while acetonitrile and nitromethane caused dramatic changes in the Cotton effects of poly-1.