Red emitting N-functionalized poly(1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole) (poly-DPP):: A deeply colored polymer with unusually large Stokes shift

New pi-conjugated polymers are described, which entirely consist of aryl-aryl-coupled 1,4-diketo-2,5-dialkyl-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) units. The alkyl groups are n-hexyl (4a) or 2-ethylhexyl (4b) groups. The polymers are synthesized using nickel-promoted and palladium-catalyzed one-pot coupling reactions starting from 1,4-diketo-2,5-dialkyl-3,6-di(4-bromophenyl)pyrrolo[3,4-c]pyrrole (dibromo-DPP) as monomer, or conventional palladium-catalyzed coupling of dibromo-DPP and the 3,6-bis(pinacolato)boronester derivative of DPP. Polymers exhibit molecular weights up to 33 000 and are excellently soluble in chloroform and toluene. Deep red solutions (lambda(max) of 4b: 525 nm) with intense red photoemission (lambda(max) of 4b: 632 nm) and unusually large Stokes shift up to 107 nm are obtained. Cyclic voltammetry indicates quasi-reversible oxidation and reduction behavior, the onset potentials of 4b are +1.03 and -0.74 V vs SCE, respectively. From these potentials, HOMO/LUMO levels of -5.47 and -3.70 eV, respectively, can be calculated. Good solubility and processability into thin films render the compounds suitable for electronic applications.