Electronic properties of poly(1,4-phenylene methylidynenitrilo-1,4-phenylene nitrilomethylidyne) (PPI)

Poly(1,4-phenylene methylidynenitrilo-1,4-phenylene nitrilomethylidyne) (PPI) was prepared and investigated using UV spectroscopy and tunneling current measurements at metal/PPI interfaces. The difference between the LUMO and HOMO level energies of PPI is determined as well as its electron affinity. The measured shift of the LUMO level of PPI relative to unsubstituted poly(p-phenylene vinylene) (PPV) agrees with semi-empirical quantum mechanical calculations performed on the dimer using the CNDO/S method which predicts a stabilization of both LUMO and HOMO levels with respect to unsubstituted PPV.