Organic semiconducting materials derived from πelectron-rich pyrroles have garnered attention in recent years for the development of organic semiconductors. Although pyrrole is the most electron-rich five-membered heteroaromatic ring, it has found few applications in organic photovoltaics and organic field-effect transistors due to synthetic challenges and instability. However, computational modeling assisted screening processes have indicated that relatively stable materials containing pyrrolic units can be synthesized without compromising their inherent electron-donating properties. In this work, we provide a complete, up-to-date review of pyrrole-containing semiconducting materials used for organic photovoltaics and organic field-effect transistors and highlight recent advances in the synthesis of these materials.

Nickel catalysts represent a low cost and environmentally friendly alternative to palladium-based catalytic systems for Suzuki–Miyaura cross-coupling (SMC) reactions. However, nickel catalysts have suffered from poor air, moisture, and thermal stabilities, especially at high catalyst loading, requiring controlled reaction conditions. In this report, we examine a family of mono- and dinuclear Ni(II) and Pd(II) complexes with a diverse and versatile α-diimine ligand environment for SMC reactions. To evaluate the ligand steric effects, including the bite angle in the reaction outcomes, the structural variation of the complexes was achieved by incorporating iminopyridine- and acenaphthene-based ligands. Moreover, the impact of substrate bulkiness was investigated by reacting various aryl bromides with phenylboronic acid, 2-naphthylboronic acid, and 9-phenanthracenylboronic acid. Yields were the best with the dinuclear complex, being nearly quantitative (93–99%), followed by the mononuclear complexes, giving yields of 78–98%. Consequently, α-diimine-based ligands have the potential to deliver Ni-based systems as sustainable catalysts in SMC.

Two p-type donor–acceptor (D–A) semiconducting small molecules were synthesized to investigate the effect of the backbone curvature on the organic field-effect transistor performance. The backbone curvature of the donor–acceptor small molecules was modified by changing the spacer group from bithiophene to thienothiophene. Bithiophene to thienothiophene spacer groups were placed between 4H-thieno[3,2-b]pyrrole (donor) and benzo[c][1,2,5]thiadiazole (acceptor) to generate TP-BT4T-TP and TP-BT2TT-TP donor–acceptor molecules. A good charge carrier mobility of 2.59 × 10–2 cm2 V–1 s–1 was measured for the curved molecule (TP-BT4T-TP), while the linear molecule analog (TP-BT2TT-TP) only gave a low mobility of 5.41 × 10–5 cm2 V–1 s–1 after annealing at 120 °C in bottom-contact bottom-gate devices. Out-of-plane grazing-incidence X-ray diffraction analysis revealed more drastic thermally induced crystallinity for TP-BT4T-TP as compared to TP-BT2TT-TP, explaining the difference observed in the performance of devices fabricated from each molecule.

Incorporating selenophene into organic semiconductors has recently shown promising results in both organic solar cells (OSCs) and organic field-effect transistors (OFETs). In most studies, replacing thiophene with selenophene has improved the performance in OSCs and OFETs. However, some other reports do not show the same trend. Therefore, the structure−property relationship of selenophene-containing semiconducting materials is still to be investigated and understood. On the other hand, reports have shown that thiophene flanked benzothiadiazole-and thieno-[3,2-b]pyrrole-based donor−acceptor−donor molecular architecture gave a banana-shaped small organic conjugated molecule with moderate OFETs performance. To understand the structure− property relationship and influence on OFETs performance, by replacing thiophene with selenophene in chalcogenopheno[3,2-b]pyrrole, we report a nonconventional fused ring system, estermonocapped selenopheno[3,2-b]pyrrole, which was coupled with chalcogenophene spacer flanked benzothiadiazole to yield two curved small organic conjugated molecules, diethyl 2,2′-(5,5′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-5,2-diyl))bis(4dodecyl-4H-selenopheno[3,2-b]pyrrole-5-carboxylate (BT-2T-2SeP) and diethyl 2,2′-(benzo[c][1,2,5]thiadiazole-4,7-diylbis-(selenophene-5,2-diyl))bis(4-dodecyl-4H-selenopheno[3,2-b]pyrrole-5-carboxylate (BT-2Se- 2SeP). This is the first report of selenopheno [3,2-b]pyrrole incorporated in donor−acceptor small conjugated organic molecules for OFETs applications. BT-2T-2SeP and BT-2Se-2SeP exhibited comparable maximum hole mobilities of 8.82 × 10 −3 cm 2 V −1 s −1 and 1.44 × 10 −2 cm 2 V −1 s −1 , respectively. Furthermore, these molecules exhibited lower threshold voltages between 0-(−5) V and high on−off current ratios of 10 4 and ∼10 5 , respectively, for BT-2T-2SeP and BT-2Se-2SeP.

Hypervalent (HV) iodine­(III) compounds with fluorine-containing ligands (F, CF3, C6F5CO2, or CF3(CF2)8CO2 (n-C9F19CO2)) reacted, in the presence of iodine or copper salts, with the double bonds in cis-1,4-polyisoprene (polyIP) to afford fluorine-containing polymers. For instance, fast iodo-fluorination of polyIP was accomplished in the presence of 4-(difluoroiodo)­toluene (4-TolIF2) and iodine. The reaction of polyIP with 1-trifluoromethyl-1,2-benziodoxol-3­(1H)-one (Togni reagent II) and copper­(I) iodide under mild conditions yielded polymers with vicinal pendant trifluoromethyl and 2-iodobenzoate groups, which were subjected to acid-promoted elimination to give a fluorine-containing unsaturated polymer. The simultaneous introduction of trifluoromethyl groups and a halogen (Cl or Br) was achieved by reacting polyIP with Togni reagent II in the presence of thionyl halide and copper­(II) salts. The alkyl chloride pendant groups in the product of the copper-mediated reaction of polyIP with thionyl chloride and Togni reagent II were subsequently converted to azide functionalities by nucleophilic substitution with NaN3, and the produced azide-containing polymer was subjected to copper­(I)-catalyzed “click” coupling reaction with a fluorescent alkyne, propargyl 4-(1-pyrenyl)­butyrate. Perfluoroacyloxy pendant groups were also introduced successfully by the reaction of polyIP with HV iodine­(III) reagents with perfluorinated carboxylate ligands, i.e., C6H5I­(O2CC6F5)2 and C6H5I­(O2C­(n-)­C9F19)2, in the presence of iodine. No significant chain degradation and/or cross-linking was observed in any of the functionalization reactions. The modified polymers showed relatively good thermal stability and high hydrophobicity, with contact angles toward water in the range of 89–116°.