Head-to-tail
regioregular poly(4-alkylthiazole)s containing silylethers in the
side-chains were synthesized via Kumada-Coupling polycondensation
of “reversed” monomers, that were metalated
at the sterically hindered 5-position. Their optical, electrochemical,
and bulk properties have been studied, and evidence is presented that
indicates the occurrence of quasi-living chain-growth behavior in
the polymerization process. Two polymers, PTzTIP and PTzDIBO, featuring triisopropylsilyl and diisobutyloctadecylsilyl
side chains, respectively, were prepared. PTzTIP is largely
insoluble, while PTzDIBO is fully soluble in common organic
solvents, including hexane, and readily gave number-averaged molecular
weights exceeding 100 kDa, corresponding to an average degree of polymerization
greater than 200, as determined via gel-permeation chromatography
(GPC) in CHCl3. The formation of a regular head-to-tail
regiostructure could be confirmed through comparison with a head-to-head–tail-to-tail
regioregular polybithiazole (PBTzTIP), synthesized via
Yamamoto-polymerization of a head-to-head-linked bithiazole. Regioregular PTzDIBO could be obtained via different polymerization protocols,
including external initiation with two new aryl-nickel-complexes,
which furnished material with particularly low polydispersities (<1.4
at M
n > 100 kDa). Furthermore, a direct
correlation between the obtained molecular weight and the monomer/catalyst
ratio was observed in series of batch polymerization experiments,
in agreement with a chain-growth polycondensation process. The incorporation
of the precatalyst–aryl moiety into the polymer chains could
be proven by comparison with a model compound. The functionalized
end-groups allowed to independently determine the molecular weight
via 1H NMR, which gave good agreement with the values obtained
from GPC, further corroborating the occurrence of chain-growth.
Conjugated
polymers are emerging as alternatives to inorganic semiconductors
for the photoelectrochemical water splitting. Herein, semi-transparent
poly(4-alkylthiazole) layers with different trialkylsilyloxymethyl
(R
3
SiOCH
2
−) side chains (PTzTNB, R =
n
-butyl; PTzTHX, R =
n
-hexyl) are applied
to functionalize NiO thin films to build hybrid photocathodes. The
hybrid interface allows for the effective spatial separation of the
photoexcited carriers. Specifically, the PTzTHX-deposited composite
photocathode increases the photocurrent density 6- and 2-fold at 0
V versus the reversible hydrogen electrode in comparison to the pristine
NiO and PTzTHX photocathodes, respectively. This is also reflected
in the substantial anodic shift of onset potential under simulated
Air Mass 1.5 Global illumination, owing to the prolonged lifetime,
augmented density, and alleviated recombination of photogenerated
electrons. Additionally, coupling the inorganic and organic components
also enhances the photoabsorption and amends the stability of the
photocathode-driven system. This work demonstrates the feasibility
of poly(4-alkylthiazole)s as an effective alternative to known inorganic
semiconductor materials. We highlight the interface alignment for
polymer-based photoelectrodes.
Annealed films of regioregular polythiazoles with tri(n-hexyl)silyloxymethyl-side-chains self-organize into crystalline lamellar domains, and show greatly enhanced electron mobility.
A series of polythiazoles (PvTzs) featuring conjugated styryl sidechains equipped with different solubilizing p‐alkoxy‐groups (OR, R = n‐octyl, n‐dodecyl, 2‐ethylhexyl, 2‐hexyldecyl) is prepared by Negishi‐coupling polycondensation. Soluble material with number‐average molecular weights of up to Mn = 8.5 kDa (polydispersity (PDI) = 1.3, degree of polymerization (DPn) ≈ 20) is obtained, with a head‐to‐tail content of the PvTzs of ≈77%, as estimated from comparison with reference polymers. The polymers exhibit optical absorption properties similar to their polythiophene analogues, while their electrochemical characterization shows a significant stabilization of their frontier orbital levels. Fluorescence measurements indicate that upon excitation of the electron rich alkoxystyryl side‐chains charge transfer onto the more electron deficient polythiazole backbone occurs. This finding is corroborated by density functional theory (DFT) calculations on oligomeric model systems, which also consistently reproduce the optical properties observed for the polymers. The potentialities of these materials for applications in organic electronics can be demonstrated by their use as donor materials in organic photovoltaic cells, which exhibit higher open circuit voltages (VOC, up to 0.86 V) than P3HT‐ or analogous polythiophene‐based cells (VOC = 0.5–0.6 V).
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