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

Synthesis and characteristic properties of polymers P1-P4 containing 1,3,4,6-tetraarylated pyrrolo[3,2-b]pyrrole-2,5-dione (isoDPP) units in the main chain are described. PI and P2 were prepared upon palladium-catalyzed polycondensation of 3,6-bis(4-bromophenyl)-1,4-bis(4-tert-butylphenyl)pyrrolo[3,2-b]pyrrole-2,S-dione (M1) or 1,4-bis(4-bromophenyl)-3,6-bis(4-tert-butylphenyl)pyrrolo[3,2-b]-pyrrole-2,5-dione (M2) and 2,2'-(9,9-dihexyl-9H-fluoren-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (M4), while P3 and P4 were synthesized upon polycondensation of 3,6-bis(5-bromothien-2-yl)-1,4-bis(4-dodecylphenyl)pyrrolo[3,2-b]pyrrole-2,5-dione (M3) and 2,5-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thiophene (MS) or 9-(2-ethylhexyl)-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)carbazole (M6). 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 (epsilon > 2 x 10(4) L mol(-1) cm(-1)) but weak fluorescence, the quantum yields being below 1%. Although P1 and P2 are isomers, their optical properties are rather different. P1 with polyconjugated backbone exhibits an absorption maximum at 409 nm, while P2 has a maximum at 360 nm due to interruption of pi-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 (P3) and 435 nm (P4). All polymers exhibit nearly irreversible oxidation and reduction behavior. Bandgaps of the polymers with phenyl-substituted isoDPP units (PI and P2) are at about 2 eV, while those of polymers with thienyl-substituted isoDPP (P3 and P4) are at about 1.5 eV.