Electronic and FTIR Spectroscopy of Controlled Chain Length Pristine and Iodine-Doped Permethylazine Oligomers
Bradford C. Sherman, Brian K. Schmitz, William B. Euler, Chemistry of Materials, 1995, 7, 806 – 812
Abstract
The electronic spectroscopy of a series of controlled chain length permethylazine oligomers, H2N-[N=C(CH3)-C(CH3)=N]x-NH2 (x = 1, 2, 3, 4, 5, 7, 11) is examined in solution and as thin films. As the chain length is increased evidence for the four pi bands expected from the dimeric repeat unit is found and this is corroborated by Hartree-Fock calculations at the 6-31G* level of the monomer (x=1) and dimer (x=2) in this series. In the thin film and in polar solvents a delocalization limit of about 4 repeat units is suggested, in agreement with FTIR results. Upon doping with gas phase iodine, thin films of all of these oligomers (x>2) develop the spectral signature of triiodide and this can be compensated for with ammonia gas. FTIR analysis of the iodine-doped thin films show that the only observed change is the development of a peak at 1505 cm–1 and that the basic geometry of the oligomers is unchanged. These results are interpreted as the formation of iodonium complexes bound to the imine nitrogen. This eliminates the bipolaron interpretation of similar spectral features found previously in iodine-doped polyazines since these oligomers are of insufficient chain length to support a bipolaron.