Synthesis and properties of Zn2+/Cd2+-directed self-assembled metallo-supramolecular polymers based on 1,4-diketo-pyrrolo[3,4-c]pyrrole (DPP) derivatives

New building blocks based on 1,4-diketopyrrolo[3,4-c] pyrrole (DPP), 2,5-bis(2-ethylhexyl)-3,6-bis(5-[p-(2,2':6',2 ''-terpyridine-4'-yl)phenyl]thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (M1) and 2,5-bis(2-ethylhexyl)-3,6-bis(4-[p-(2,2':6',2 ''-terpyridine-4'-yl) phenyl]phenyl)pyrrolo[3,4-c] pyrrole-1,4(2H,5H)-dione (M2) were synthesized by the Suzuki Pd-catalyzed cross-coupling reaction. Under moderate conditions, directed self-assembly polymerizations by the transition metal ions Zn2+ and Cd2+, respectively, were carried out. The metallo-supramolecular polymers P1Zn, P1Cd, P2Zn and P2Cd were obtained and fully characterized. The supramolecular polymers P2Zn and P2Cd, containing DPP modified by a phenyl unit, showed absorption maxima at about 504 and 506 nm in films. In contrast, the polymers P1Zn and P1Cd, in which the thiophene moiety-modified DPP was introduced, exhibited strong and broad visible absorption over 300-800 nm with maxima at about 601 and 598 nm and shoulder peaks at about 665 and 671 nm, respectively. The low band gaps estimated from CV of 1.52, 1.51, 1.58 and 1.58 eV for P1Zn, P1Cd, P2Zn and P2Cd, respectively, are also reported.