| Abstract
| - The control of the position of the energy levels in conducting polymers through fluorinesubstitution is demonstrated. The synthesis of four different monomers and polymers of the poly(terphenylenevinylene) type is presented. The synthetic procedure started with 4-bromo-2,5-dioctylphenylboronic acid (1) coupled by the Suzuki method with 4-bromobenzaldehyde to give 4‘-bromo-2‘,5‘-dioctyl-4-formylbiphenyl (2) that was again coupled by the Suzuki method with 4-diethylphosphonylmethylphenylboronic acid and 4-cyanomethylphenylboronic acid to give the monomers 4‘ ‘-diethylphosphonylmethyl-2‘,5‘-dioctyl-4-formylterphenyl (3) and 4‘ ‘-cyanomethyl-2‘,5‘-dioctyl-4-formylterphenyl (4). Thepartially fluorinated analogous monomers were prepared similarly employing 2,5-difluoro-3,6-diperfluorooctyl-1,4-dibromobenzene. This gave 4-bromo-2,5-difluoro-3,6-diperfluorooctyl-4‘-diethylphosphonylmethylbiphenyl (5) and 4-bromo-2,5-difluoro-3,6-diperfluorooctyl-4‘-cyanomethylbiphenyl (6). Compounds5 and 6 were both subjected to Suzuki couplings with 4-formylphenylboronic acid to give respectively4-formyl-2‘,5‘-difluoro-3‘,6‘-diperfluorooctyl-4‘ ‘-diethylphosphonylmethylterphenyl (7) and 4-formyl-2‘,5‘-difluoro-3‘,6‘-diperfluorooctyl-4‘ ‘-cyanomethylterphenyl (8). The monomers 3, 4, 7, and 8 were polymerizedto give the polymers poly(2‘,5‘-dioctyl-4,4‘ ‘-terphenylenevinylene) (9), poly(2‘,5‘-dioctyl-4,4‘ ‘-terphenylenecyanovinylene) (10), poly(2‘,5‘-difluoro-3‘,6‘-diperfluorooctyl-4,4‘ ‘-terphenylenevinylene) (11), and poly(2‘,5‘-difluoro-3‘,6‘-diperfluorooctyl-4,4‘ ‘-terphenylenecyanovinylene) (12). Thin films of the polymers onpolycrystalline gold substrates were subjected to ultraviolet photoelectron spectroscopy, and the ionizationpotentials were determined to be 4.85, 4.60, 4.75, and 5.95 eV for 9, 10, 11, and 12 respectively. Thepositions of the highest occupied energy levels were determined to be 1.45, 2.65, 2.25, and 3.05 eV lowerthan that of gold for 9, 10, 11, and 12, respectively. Fluorine and cyano substitution thus allows for anenergy level tuning by as much as 1.6 eV.
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