| Summary: | The synthesis and characterization of a series of functionalized head-to-tail
regioregular poly-3-alkylthiophenes are reported. The influences of the structure and
functional groups on the optical and electronic properties are investigated with NMR,
absorption, emission and infrared spectroscopy, gel permeation chromatography, and
cyclic voltammetry.
A regioregular poly-3-alkylthiophene (Poly-1) was synthesized via Grignard
Metathesis polymerization conditions. Poly-1 contains bromide groups as sites of latent
reactivity along the polymer backbone through which additional reactions were carried
out post-polymerization. The bromide was converted to an azide group (Poly-2) which
was further functionalized via Click chemistry with a variety of functional groups.
Click chemistry was carried out using the Huisgen 1,3-dipolar cycloaddition
reaction. Post-polymerization functionalization of Poly-2 provided a facile method for
preparing a variety of related functional polymers, each with identical average chain
length, average polydispersity and average distribution of monomers. Preparation of
Poly-3a, -3b, and -3c, demonstrated the utility of the Click reaction for modifications
with a variety of functional groups.
A series of poly-3-alkylthiophene analogs (Poly-1 - Poly-11) were characterized
by absorption and emission spectroscopies and the spectra were found to be dependant on
regioregularity along the polymer backbone. The UV-vis absorption maxima, varied with
the percentage of head-to-tail couplings in relation to the extent of conjugation.
The series of dithienylethene functionalized oligo- (71) and polymer analogs
(Poly-4, Poly-7 and Poly-11) displayed fluorescence quenching capabilities upon
photoinduced ring closing of the dithienylethene moiety via energy transfer. The extent
of quenching was determined to be dependent on both the length and structure of the
backbone. Extended conjugation contributed to amplified fluorescence quenching as
observed by complete fluorescence quenching of Poly-4.
The functionalization of the Poly-2 with the stable free nitroxide radical 2,2,6,6-
tetramethylpiperdine-1-oxyl is described. The resulting polymer, Poly-12, was
characterized with cyclic voltammetry and IR spectroscopy. Electrochemical deposition
of thin films of Poly-12 onto various working electrodes is described. The thin films were
investigated for potential charge storage via galvanostatic charge/discharge cycles. IR
spectroscopy revealed that the nitroxide radical had sensitized the polythiophene
backbone to oxidation, resulting in irreversible damage to the polymer and reduced
charge storage capacity.
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