Molecular wire behavior in pi-stacked donor-bridge-acceptor tertiary arylureas.

The synthesis, structure, and electronic properties of a series of tertiary polyarylureas possessing pyrene and dimethylaniline capping groups separated by zero-to-four phenylenediamine bridging groups are described. These molecules adopt folded π-stacked structures. The dynamics of photoinduced charge separation and charge recombination are investigated by femtosecond broadband pump−probe spectroscopy. The structure lacking a bridging group displays ultrafast charge separation (within 2 ps) and charge recombination typical of stacked dyad systems. Structures having one-to-four bridging groups undergo charge separation with decay times of 8−21 ps and charge recombination with decay times of 60−120 ps that are only weakly dependent upon the distance between the pyrene and dimethylaniline capping groups. This behavior is similar to that of wire-like systems having extended conjugated bridges and provides the first example of wire-like behavior in a π-stacked donor-bridge-acceptor system.