Optoelectronic properties of quasi-linear, self-assembled platinum complexes: Pt-Pt distance dependence

Charge-carrier mobilities of various self-assembled platinum complexes were measured by time-resolved microwave conductivity techniques in the temperature range -80 to +100°C. Eight compounds were investigated in the present study, including the original Magnus' green salt ([Pt(NH₃) ₄][PtCl₄]) and derivatives with the general structure [Pt(NH₂R)₄][PtCl₄], where R denotes an alkyl side chain. In one instance, the chlorines were substituted with bromines. For these complexes, which all consist of a linear backbone of platinum atoms with Pt-Pt distances, d, varying from 3.1 to ≥ 3.6 Å, a strong, inverse correlation was found between d and the one-dimensional charge-carrier mobility, σμ_1D. The highest value of σμ_1D at room temperature was observed for R = (S)-3,7-dimethyloctyl (dmoc) with σμ_1D ≥ 0.06 cm² V^-1 s^-1. Almost all materials exhibited a charge-carrier mobility that was relatively independent of the temperature over the range studied. One exceptional compound (R = (R)-2-ethylhexyl) showed a pronounced negative temperature dependence of the charge-carrier mobility; upon decreasing the temperature from +100°C to -80°C the charge-carrier mobility increased by a factor of about ten.