Figure 4 (a) Chemical
structure; (b) Single-crystal data of NTI-EH and NTI-Bu; (c) Device
thermal stability of polymers; (d) Aging of hot PNTB-HD:N3, PNTB-2T:N3
and PM6:N3 chloroform solution (identical with condition for device
fabrication) for 2 h at room temperature. Reproduced with
permission.[33] Copyright, 2022 Elsevier
Ltd.
3.2.
Thieno-[3,4-c]-pyrrole-4,6-dione
(TPD) based polymers.
TPD unit was first synthesized by Sicé in 1954 by treating
thiophene-3,4-dicarbocylic acid with ammonia.[72]Tour and co-workers first reported TPD-based conjugated copolymers in
1997.[73] TPD unit has the advantages of easy
synthesis, high coplanarity, and strong electron-withdrawing
ability.[46] In addition, Various side groups can
be introduced into the N-site of TPD to tune solubility of the resulting
polymer and morphology of blend films.[39,46] To
date, four synthetic routes have been reported for the preparation of
TPD (Scheme 2) . Bjørnholm et
al. [74] reported the synthesis of TPD from
starting materials of 3, 4-dibromothiophene, which was converted to 3,
4-dicyanothiophene by Rosenmund-von Braun reaction with cuprous cyanide
(Synthetic route 1). The alkaline hydrolysis of 3, 4-dicyanothiophene
result in thiophenedicarboxylic acid, and then reflux in acetic
anhydride to produce cyclic anhydride. The TPD was synthesized by
treating 4-amino-thiophene-3-carboxylic acid with thionyl chloride. The
synthesis of TPD dimer was based on the bromination of the TPD with 1
equiv of NBS, however, it makes the conditions hard to control to obtain
the desired product with a good yield. In 2011, an efficient synthetic
route was reported for the preparation of the
1-iodo-5-alkyl-4H-thieno[3,4-c] pyrrole-4,6(5H)-dione (TPD-I) by
Leclerc et al. .[75] They
synthesized3-ethyl 4-methyl 2-aminothiophene-3,4-dicarboxylate by the
Gewald reaction between methyl 2-oxopropanoate and ethyl cyanoacetate.
Then, the Sandmeyer-type reaction makes the amine of 3-ethyl 4-methyl
2-iodothiophene-3,4-dicarboxylate substituted by an iodide. Followed by
acidic hydrolysis to obtain 3-ethyl 4-methyl
2-iodothiophene-3,4-dicarboxylate. Finally,
1-iodo-5-alkyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD-I) was
obtained via pyrroledione ring formation (Synthetic route 2). In 2015,
Shinichiro Fuse et al. reported the synthesis of TPD through a
Pd-catalyzed carbonylative amidation reaction from commercially
available 3,4-dibromothiophene in a yield of 63 % (Synthetic route
3).[76] It should be noted it is the most
straightforward synthetic route to synthesize TPD by one-step reaction.
In 2023, Min et al. reported a synthetic route of DT-TPD through
a two-step reaction in a yield of 31 %.[77] The
key ring forming reaction was conducted by heating the mixture of
4-alkylthiophene-2-carbaldehyde, S8, 1-methylpyrrolidine-2,5-dione,
2-aminobenzimidazole, NH4I,
K2CO3, N-methyl-2-pyrrolidone and
H2O in 140 °C for 48 hours, yielding DT-TPD (Synthetic
route 4).
Scheme 2 Synthetic route
of TPD.
Leclerc et al. synthesized
the a TPD-based polymer, and afforded a PCE of 5.5 % when blended with
PC71BM in 2010.[78] After that,
Thieno[3,4-c]pyrrole-4,6-dione (TPD) unit as an electron-deficient
unit has been widely used to construct conjugated polymers for
application in fullerene and non-fullerene based
OSCs.[39,46],[79,80] Figure 5 summarizes the
structures of typical TPD-based polymers and relevant properties are
listed in Table 2. Wang et al. [81]synthesized PBDT-TPD and PBDTS-TPD based on the BDT and TPD, and PCEs of
6.8 % and 7.7 % were achieved by blending with PNDI-T. Gao et
al. [82] synthesized polymers PBDTT-TPD and
PBDT-TPD. Compared with the alkoxy-modified polymer PBDT-TPD, the
alkyl-thienyl modified polymer PBDTT-TPD possesses deeper HOMO energy
level, higher extinction coefficient and better hole transport property,
leading to a higher PCE of 7.15 % for PBDTT-TPD:IDIC based OSCs.