Defects in the electronic structure of poly (p-phenylene vinylene): Electronic spectra, electrochemical behavior, and molecular orbital calculations

Abstract

The electronic spectrum of thin films of poly(p‐phenylene vinylene) (PPV) in an insulating neutral form exhibits three absorption bands with maxima at 6.12, 5.06, and 3.08 eV. The first two maxima are related to localized molecular states and the broad band at 3.08 eV is described in terms of a vibrationally coupled excitonmodel. Upon electrochemicaldoping of PPV, two additional absorption bands appear at 0.80 and 2.10 eV which are associated with a dication whose charge is spread over a few monomer units. Thin films of PPV can be electrochemically converted from the oxidized (conducting) form to the neutral (insulating) form repeatedly in LiAsF6/propylene carbonate solution without evidence of decomposition. The E 0 measured using cyclic voltammetry is 3.85 V vs a Li/Li+ reference electrode; however, the observed optically active defects occur in a region of higher potential.