Comparison of the Optical and Electrochemical Properties of Bi(perylene diimide) s Linked through Ortho and Bay Positions

The Ullmann homocoupling of 2-bromoperylene diimides (PDIs) gave [2,2'-biperylene]3,4: 9,10: 3', 4': 9', 10'-tetrakis(dicarboximide) s, 2,2'-bi(PDI) s, and the Suzuki coupling of a PDI-2-boronic ester and a 1bromo- PDI gave a [1,2'-biperylene]-3,4: 9,10: 3', 4': 9', 10'tetrakis( dicarboximide), 1,2'-bi(PDI). These were compared with [1,1'-biperylene]-3,4: 9,10: 3', 4': 9', 10'-tetrakis( dicarboximide) s, 1,1'-bi(PDI) s. Solution absorption spectra suggest that the PDIs in 2,2'-bi(PDI) s are more planar and less strongly coupled than those in 1,1'-bi(PDI) s, which is consistent with density functional theory calculations. 2,2'Bi( PDI) s are less easily reduced than 1,1'-and 1,2'-bi(PDI) s by ca. 70-90 mV. Bulk heterojunction organic solar cells incorporating a 2,2'-bi(PDI) acceptor behaved similarly to those employing its 1,1'-bi(PDI) analogue.