Highly Luminescent Polymers Containing the 2,3,5,6-Tetraarylated Pyrrolo [3,4-c] pyrrole-1,4-dione (N-Aryl DPP) Chromophore in the Main Chain

Synthesis and characteristic properties of polymers P-1-P-3 are described containing the 2,3,5,6-tetraarylated pyrrolo[3,4-c]pyrrole-1,4-dione unit in the main chain. P-1 is prepared from 2,5-bis(4-t-butylphenyl)-3,6-bis(4'-bromophenyl)pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) and 9,9-di-n-hexylfluorene-2,7'-bispinacolato-boronester 3, P-2 from 2,5-bis(4'-bromo-phenyl)-3,6-bis(4-t-butylphenyl)-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP2) and 3, and P-3 from DPP1, 3, and 2,5-bis(n-hexyloxybenzene)-1,4-bispinacolatoboronester 4 via Pd-catalyzed Suzuki coupling. Molecular weights of the polymers are about 8000-10000 Da. All polymers are soluble in common organic solvents such as toluene, chloroform, dichloromethane, tetrahydrofuran (THF), and dimethylsulfoxide (DMSO) and exhibit a strong fluorescence with Stokes shift up to 56 nm (P-3) and quantum yield up to 81% (P-1). Although P-1 and P-2 are isomers, their optical and electrochemical properties are very different. P-1 with a polyconjugated carbon backbone exhibits absorption and fluorescence maxima of 516 and 569 nm, respectively, which are bathochromically shifted by 15-25 nm with regard to monomer DPP1. In P-2, the pi-conjugation of the backbone is interrupted by the lactam N-atoms, so that absorption and fluorescence are similar to those of monomer DPP2 (489 and 531 nm, respectively). Properties of polyconjugated copolymer P-3 are similar to those of P-1, Band gaps of P-1 and P-2 are 2 and 2.3 eV, respectively. Cyclovoltammetric studies indicate irreversible oxidation and reduction cycles.