Electrochemical polymerization of 1,3,4,6-tetraarylpyrrolo[3,2-b]pyrrole-2,5-dione (isoDPP) derivatives

New pi-conjugated polymers containing 1,3,4,6-tetraarylpyrrolo[3,2-b] pyrrole-2,5-dione (isoDPP) units in the main chain were prepared by electrochemical polymerization of isoDPP-based monomers M1-M3. Monomers M1 and M2 were previously obtained upon palladium-catalyzed Suzuki cross-coupling of dibromo-isoDPP derivatives 3,6-bis(5-bromothiophen-2-yl)-1,4-bis(4-tert-butylphenyl) pyrrolo-[3,2-b]pyrrole-2,5-dione 1a, or 3,6-bis(5-bromothiophen-2-yl)-1,4-bis(4-hexylphenyl)-pyrrolo-[3,2-b] pyrrole2,5-dione 1b and 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolanyl)-3-hexylthiophene. Monomer M3 was synthesized by Stille coupling of 1a and 2-(tributylstannyl)-4-octylthiophene. The yields were about 88%. M1-M3 were obtained as dark red powders with excellent solubility in organic solvents. The electrochemical polymerization was carried out under potentiodynamic conditions, i. e., the potential was repeatedly cycled between 0.0 (or -0.2) V and 1.2 V vs. ferrocene (FOC). The polymers P1-P3 precipitated as stable, insoluble, well adhering thin films on ITO-coated glass or glassy carbon electrodes. P1-P3 exhibit broad absorption spectra with maxima between 526 and 629 nm. They are non-fluorescent. Cyclovoltammetric studies indicate reversible oxidation and reduction behavior. Anodic cycling is accompanied with reversible colour changes of polymer films. The oxidation potentials are between 0.27 and 0.71 V vs. FOC, and the reduction potentials are between -1.21 and -1.69 V. The band gaps of the polymers are between 1.51 and 1.62 eV. Due to their optical and electrochemical properties the polymers might be useful as active materials in electrochromic displays

Deeply Colored Polymers Containing 1,3,4,6-Tetraarylpyrrolo[3,2-<i>b</i>]pyrrole-2,5-dione (IsoDPP) Units in the Main Chain

Synthesis and characteristic properties of polymers <b>P1</b>–<b>P4</b> containing 1,3,4,6-tetraarylated pyrrolo­[3,2-<i>b</i>]­pyrrole-2,5-dione (isoDPP) units in the main chain are described. <b>P1</b> and <b>P2</b> were prepared upon palladium-catalyzed polycondensation of 3,6-bis­(4-bromophenyl)-1,4-bis­(4-<i>tert</i>-butylphenyl)­pyrrolo­[3,2-<i>b</i>]­pyrrole-2,5-dione (<b>M1</b>) or 1,4-bis­(4-bromophenyl)-3,6-bis­(4-<i>tert</i>-butylphenyl)­pyrrolo­[3,2-<i>b</i>]­pyrrole-2,5-dione (<b>M2</b>) and 2,2′-(9,9-dihexyl-9<i>H</i>-fluoren-2,7-diyl)­bis­(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (<b>M4</b>), while <b>P3</b> and <b>P4</b> were synthesized upon polycondensation of 3,6-bis­(5-bromothien-2-yl)-1,4-bis­(4-dodecylphenyl)­pyrrolo­[3,2-<i>b</i>]­pyrrole-2,5-dione (<b>M3</b>) and 2,5-bis­(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)­thiophene (<b>M5</b>) or 9-(2-ethylhexyl)-2,7-bis­(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)­carbazole (<b>M6</b>). Deeply colored polymers with molecular weights between 3.5 and 22 kDa were obtained. The polymers were soluble in common organic solvents such as dichloromethane, chloroform, and tetrahydrofuran. All polymers exhibit broad absorption bands with high extinction coefficients (ϵ > 2 × 10⁴ L mol^–1 cm^–1) but weak fluorescence, the quantum yields being below 1%. Although <b>P1</b> and <b>P2</b> are isomers, their optical properties are rather different. <b>P1</b> with polyconjugated backbone exhibits an absorption maximum at 409 nm, while <b>P2</b> has a maximum at 360 nm due to interruption of π-conjugation at the lactam N atoms. The presence of thienyl-isoDPP units in the backbone causes a red-shift of the absorption to 489 nm (<b>P3</b>) and 435 nm (<b>P4</b>). All polymers exhibit nearly irreversible oxidation and reduction behavior. Bandgaps of the polymers with phenyl-substituted isoDPP units (<b>P1</b> and <b>P2</b>) are at about 2 eV, while those of polymers with thienyl-substituted isoDPP (<b>P3</b> and <b>P4</b>) are at about 1.5 eV

Synthesis and characterization of 1,3,4,6-tetraarylpyrrolo[3,2-b]-pyrrole-2,5-dione (isoDPP)-based donor-acceptor polymers with low band gap

The synthesis of new pi-conjugated donor-acceptor (D-A) polymers containing tetraaryl-diketopyrrolo[3,2-b]-pyrrole (isoDPP) as the building block is described. Polymers were prepared upon palladium-catalyzed Stille coupling of 3,6-bis(5-bromothien-2-yl)-1,4-diphenyl-pyrrolo[3,2-b]pyrrole-2,5-dione (M1) with 4,4'-bis(2-ethylhexyl)-5,5'-bis(trimethyltin)dithieno[3,2-b:2',3'-d]silole (M2) or (4,8-bis-(2-ethylhexyloxy)benzo [1,2-b:4,5-b]dithiophene-2,6-diyl)bis(trimethylstannane) (M3). The polymers exhibit low band gaps of 1.53 and 1.67 eV, broad absorption bands with maxima of 523 nm and 620 nm, and high extinction coefficients of 6.5 x 10(4) L mol(-1) cm(-1), and 2.6 x 10(4) L mol(-1) cm(-1), respectively. Low fluorescence quantum yields between 0.13% and 0.82% were detected. Quantum chemical calculations indicated a nearly planar backbone with highly delocalized HOMO orbitals and localization of the LUMO electrons at the thienyl-isoDPP units. The X-ray structure analysis of M1 indicated a dihedral angle of 14.1 degrees between the thienyl groups and the isoDPP core, and a 76.6 degrees dihedral angle of the lactam phenyl group and the isoDPP core, the latter preventing any pi-stacking of the monomers. The polymers show high glass transitions (T-g) and excellent thermal stability. Photoirradiation studies indicate that the polymers are extremely stable to UV and visible light in solution. Spectroelectrochemical studies indicated a reversible electrochromism with isosbestic point near 710 nm