Cyclopenta[<i>c</i>]thiophene-Based D–A Conjugated Copolymers: Effect of Heteroatoms (S, Se, and N) of Benzazole Acceptors on the Properties of Polymers

Three new donor–acceptor (D–A) type copolymers <b>P1</b>, <b>P2</b>, and <b>P3</b> have been synthesized by Stille condensation between the distannyl derivative of thiophene-capped cyclopenta­[<i>c</i>]­thiophene (CPT) with 4,7-dibromo­[2,1,3]­benzothiadiazole, 4,7-dibromo­[2,1,3]­benzoselenadiazole, and 4,7-dibromo­[2,1,3]­benzotriazole, respectively. These new CPT-based D–A copolymers showed an interesting trend of visible color (red, green, and blue) in solution as the acceptor was varied keeping the donor constant. The optical band gaps of the polymers, which were estimated by measuring the absorption onset in the UV–vis spectra of the film, were found to be 1.57, 1.44, and 1.86 eV for <b>P1</b>, <b>P2</b>, and <b>P3</b>, respectively. DFT calculations correlated the strength of the acceptors with the interesting trend in the colors of these (D)_nonvariant–(A)_variant copolymers. Compared with the solution, the film state absorption of <b>P2</b> and <b>P3</b> was significantly red-shifted compared to that of <b>P1</b>, indicating the presence of strong interchain interactions due to efficient self-π-stacking in the solid state

Solution Processable Benzooxadiazole and Benzothiadiazole Based D‑A‑D Molecules with Chalcogenophene: Field Effect Transistor Study and Structure Property Relationship

We present here the physicochemical characterization of a series of D-A-D type molecules which comprise benzooxadiazole (BDO) and benzothiadiazole (BDT) core symmetrically linked to two aromatic-heterols (furan (F), thiophene (T) and selenophene (Se)) at 4 and 7-positions. The molecular structures of four compounds <b>2</b> (T-BDO-T), <b>3</b> (Se-BDO-Se), <b>5</b> (T-BDT-T), and <b>6</b> (Se-BDT-Se) were determined by single-crystal X-ray diffraction. The combination of chalcogen atoms of benzochalcogenadiazole and chalcogenophene in D-A-D molecules has significant impact on their molecular packing in crystal structures. Structural analyses and theoretical calculations showed that all the molecules are nearly planar. Crystal structures of <b>2</b>, <b>3</b>, <b>5</b>, and <b>6</b> showed significant short range interactions such as π···π, CH···π, S···π, Se···π, N···H, O···H, S···H, Se···H, S···O, and Se···N interactions, which influence crystal packing and orientation of the capped aromatic-heterol rings with respect to the central BDO or BDT unit. The π-stacking interactions have been observed via intermolecular overlap of the donor with acceptor units of the adjacent molecules which facilitate the charge transport process. Good thermal stability and solubility in common organic solvents make them good candidate for flexible electronics. Interestingly, the molecules <b>2</b>, <b>3</b>, and <b>6</b> have the propensity to form ordered crystallites when sheared during the drying process in the thin films. Devices based on these solution processable all organic FETs demonstrated hole mobility as high as 0.08 cm² V^–1 s^–1 and <i>I</i>_on/<i>I</i>_off ratio of 10⁴

Solution Processable Benzooxadiazole and Benzothiadiazole Based D‑A‑D Molecules with Chalcogenophene: Field Effect Transistor Study and Structure Property Relationship

We present here the physicochemical characterization of a series of D-A-D type molecules which comprise benzooxadiazole (BDO) and benzothiadiazole (BDT) core symmetrically linked to two aromatic-heterols (furan (F), thiophene (T) and selenophene (Se)) at 4 and 7-positions. The molecular structures of four compounds <b>2</b> (T-BDO-T), <b>3</b> (Se-BDO-Se), <b>5</b> (T-BDT-T), and <b>6</b> (Se-BDT-Se) were determined by single-crystal X-ray diffraction. The combination of chalcogen atoms of benzochalcogenadiazole and chalcogenophene in D-A-D molecules has significant impact on their molecular packing in crystal structures. Structural analyses and theoretical calculations showed that all the molecules are nearly planar. Crystal structures of <b>2</b>, <b>3</b>, <b>5</b>, and <b>6</b> showed significant short range interactions such as π···π, CH···π, S···π, Se···π, N···H, O···H, S···H, Se···H, S···O, and Se···N interactions, which influence crystal packing and orientation of the capped aromatic-heterol rings with respect to the central BDO or BDT unit. The π-stacking interactions have been observed via intermolecular overlap of the donor with acceptor units of the adjacent molecules which facilitate the charge transport process. Good thermal stability and solubility in common organic solvents make them good candidate for flexible electronics. Interestingly, the molecules <b>2</b>, <b>3</b>, and <b>6</b> have the propensity to form ordered crystallites when sheared during the drying process in the thin films. Devices based on these solution processable all organic FETs demonstrated hole mobility as high as 0.08 cm² V^–1 s^–1 and <i>I</i>_on/<i>I</i>_off ratio of 10⁴

Charge Delocalization in a Homologous Series of α,α′-Bis(dianisylamino)-Substituted Thiophene Monocations

A homologous series of three molecules containing thiophene, bithiophene, and terthiophene bridges between two redox-active tertiary amino groups was synthesized and explored. Charge delocalization in the one-electron-oxidized forms of these molecules was investigated by a combination of cyclic voltammetry, near-infrared optical absorption spectroscopy, and EPR spectroscopy. All three cation radicals can be described as organic mixed-valence species, and for all of them the experimental data are consistent with strong delocalization of the unpaired electron. Depending on what model is used for analysis of the optical absorption data, estimates for the electronic coupling matrix element (<i>H</i>_<i>AB</i>) range from ∼5000 to ∼7000 cm^–1 for the shortest member of the homologous series. According to optical absorption and EPR spectroscopy, even the terthiophene radical appears to belong either to Robin–Day class III or to a category of radicals commonly denominated as borderline class II/class III systems. The finding of such a large extent of charge delocalization over up to three adjacent thiophene units is remarkable