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| Figure 1. Synthesis of building block (1). |
Speaking of Organic Electronics, I would like to share with
you another recent article regarding some interesting organo-phosphorus
conjugated compounds. [1]
In the paper, the researchers have developed synthetic
routes towards novel phosphorus-containing π-conjugated compounds, by using an
interesting phosphorus reagent known as (Tipp)P(SiMe3)2
(Figure 1). It was great to observe that the phosphorus compound (1) was not as
air-sensitive as one might usually expect. Due to the presence of the two
electron-withdrawing carbonyl groups, the yellow-colored compound (1) was
stable enough to survive column chromatography.
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| Figure 2. Building up the conjugated pathway, as in (2). |
On the other hand, the DAD (Donor-Acceptor-Donor) type
compound (2) was synthesized by a Stille coupling at elevated temperature (Figure 2). It should
be noted that the (mono or bis) tributylstannyl-thiophene is often a good candidate in these
coupling reactions, especially when the thiophene units are need for organic
electronics or functional materials. It is also interesting to note that the
presence of the bulky TIPP group is essential for a successful coupling in this
case.
X-ray crystallographic structures have been obtained for
some of the compounds, and UV/vis spectra and cyclic voltammograms have also
been acquired. When these compounds were compared with their corresponding
nitrogen analogues, the LUMO energies of the organo-phosphorus compounds were
found to be lower. The observations implied σ*-π* electronic couplings in these
compounds. These phosphorus compounds were highly stable from TGA studies
(likely due to the 2 carbonyl EWGs), which made them potential candidates for
uses as organic materials.
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| Figure 3. Synthesis of the heavily conjugated organic molecule (3). |
For the next stage, the compound (2) was used to synthesize
the conjugated polymer (3) though sequential Stille coupling reactions (Figure 3). The
researchers found that the optical bandgap of (3) was much narrower than its
nitrogen counterpart. So, this polymer should be a great contender as a low
bandgap conjugated polymer.
I like this paper because the novel organo-phosphorus
compound looks interesting and useful to me. In the past, I have read about
phospholes, and also some of the zirconium-based methods for their syntheses. A
novel strategy has been used in this paper, and this approach is something I am
not aware of. As a researcher working a lot with phosphines and
phosphorus-based compounds, I find this article a rewarding one to read!
by Ed Law
27/9/2016
1. Thieno[3,4-c]phosphole-4,6-dione:
A Versatile Building Block for Phosphorus-Containing
Functional π-Conjugated Systems
Youhei Takeda, Kota
Hatanaka, Takuya Nishida, and Satoshi Minakata
Chem. Eur. J., 2016
DOI:
10.1002/chem.201602392
