Three different liquid crystal (LC) perylene diimides were investigated with respect to the optical and physical characteristics of their thin films. Films were prepared by spin-coating, vacuum evaporation, and Langmuir−Blodgett (LB) techniques on substrates such as microscope glass, indium−tin oxide-coated glass and highly oriented pyrolytic graphite. Films were characterized by polarized optical microscopy, absorption and fluorescence emission spectroscopy, and X-ray diffraction. The self-organizing ability of the LC perylene diimides allows them to rapidly reach a stable, low-energy configuration, unlike many thin film materials, and reveals that they are driven to organize and orient in a highly specific fashion, independent of substrate or deposition method. The molecules tend to form a slipped stack arrangement that maximizes attractive π−π electronic interactions, with the π−π stacking axis oriented parallel to the substrate. Relative to the substrate plane, the LC 1 perylene cores are tilted ∼47° along the stacking axis and ∼58° perpendicular to this direction. The two other LCs have similar structures. An analysis of the intermolecular electronic and steric interactions, and of the interactions between the molecules and the substrates, is proposed to explain why this is such a strongly preferred orientation. The implications for the potential use of such molecules in electronic and photovoltaic applications is discussed.

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With a view to the miniaturization of ion-selective electrodes (ISEs), thin (10−20 μm) polymer membranes are directly contacted to Au covered with a redox-active, lipophilic self-assembled monolayer (SAM). Several homogeneous and mixed monolayers are characterized by reflection−absorption infrared spectroscopy, ellipsometry, scanning tunneling microscopy, cyclic voltammetry, and contact angle measurements. These Au/thiol surfaces are combined with different K+-selective sensing membranes based on poly(vinyl chloride) (PVC), polyurethane (PUR), or PVC/PUR blends as a matrix and valinomycin as an ionophore. The sensors are investigated with regard to their potential stability in the presence of O2 and redox-active species. The occurrence of potential drifts upon changing the conditioning KCl solution to a NaCl solution is used as an indicator for the formation of an aqueous film between the membrane and Au/SAM. Stable systems are obtained with mixed monolayers (advancing contact angle θa ≈ 83°) and PVC membranes with a lower than usual plasticizer content (33 wt %), the ternary systems PVC/PUR/plasticizer (1:1:1), and PUR with 33 wt % plasticizer. On the other hand, a water film is formed between Au/SAM and conventional PVC membranes having 66% plasticizer and with less lipophilic monolayers uniquely based on a redox-active compound (θa ≈ 70°). The new solid-contact ISEs are promising both for miniaturization and for improving lower detection limits.