Synthesis and characteristics of poly[N,N′-diphenyl-N,N′-bis(4-aminobiphenyl)-(1,1′-biphenyl)-4,4′-diamine pyromellitimide] as a hole injecting and transporting layer for hybrid organic light-emitting device

A novel hole injecting and transporting polymer, poly [N,N'-diphenyl-N,N'-bis(4-amino-biphenyl)-(1,1'-biphenyl)-4,4'-diamine pyromellitimide] (PMDA-DBABBD PI), was obtained by thermal imidization from its poly(amic acid) (PAA) made by the reaction of pyromellitic dianhydride with the DBABBD that was chemically reduced from N,N'-diphenyl-NX-bis(4-nitrobiphenyl)-(1,1'-biphenyl)-4,4'diamine synthesized through the palladium-catalyzed amination. The materials were characterized by using H-1 NMR, C-13 NMR, FT-IR, HR GC-MS, EA, and DSC. The characteristics of the PAA or PI thin films were investigated with XPS and an impedance spectroscopy. The hybrid light-emitting devices (HOLEDs) with the PAA and PI thin films were fabricated to examine the performance of the polymeric thin films as a hole injecting and transporting layer. The PI thin film having the glass transition temperature of 200 degreesC showed stable characteristics in the application for the HOLED whereas the PAA thin film seemed to be unstable. The power efficiency of the HOLED with the PI thin film was 0.23 cd/A at 4000 cd/m(2).