Polyyne-Type Materials - Polyynes: Synthesis, Properties, and Applications - page 201

SCHEME 10.3 General procedure for synthesis of PAEs.

The method for the synthesis of PAEs commonly uses a Pd-catalyzed
Sonogashira-Hagihara coupling of terminal alkynes with aromatic bromides
or iodides in amine solvents, and another is metathesis by using W or Mo
complexes (Scheme 10.3). The former is suitable for synthesizing various
types of alternate co-polymers by combination of Ar 1 and Ar 2 , and the latter
has the advantage of preparing high molecular weight PAEs.
The main interest in soluble PAEs has historically been their electronic
properties as conjugated polymers. The longest absorption band is due
to a p - p * transition that corresponds to a HOMO-LUMO energy gap of
the polymer. The max values of PAEs change from about 300 to 500 nm

by combination of substituents (alkyl, alkoky, ester etc.) and arylene
( p-phenylene, m-phenylene, thienylene, etc.) of PAEs. Further degrees of
polymerization and the solvent used frequently influence the

max value. In a

filmy solid state, the absorption max observed in solution bathochromically

shifts to longer wavelengths, which largely depend on the morphology of
polymer in the solid state.