Two-dimensional charge delocalization in X-shaped phenylenevinylene oligomers

A combined experimental and theoretical study of the optoelectronic properties of charged two-dimensional X-shaped phenylenevinylene oligomers (X-mers) is presented. Cations and anions of X-mers were produced by irradiation of solutions with high-energy electron pulses. The optical absorption spectra were measured using time-resolved visible/near-infrared spectroscopy in the range of 500-1600 nm (0.8-2.5 eV). The optical absorption spectra were also calculated using the singly excited configuration interaction method with an intermediate neglect of differential overlap reference wave function (INDO/s-CIS) together with a density functional theory (DFF) optimized geometry. The INDO/s-CIS calculations reproduce the main absorption features of charged X-mers near 1.6-1.7 eV. The charge distributions calculated with DFT show that the excess positive charge is mostly localized on the phenylene units containing methoxy substituents. In contrast, the excess negative charge is delocalized over the entire oligomer. Charge-transport calculations indicate that high charge carrier mobilities can be achieved for transport along stacks of X-mers at small mutual twist angles.