IR-visible sum-frequency generation (SFG) spectroscopy has been used in a total internal reflection geometry to study the molecular structure of polystyrene (PS) at PS/sapphire and PS/air interfaces, simultaneously. The symmetric vibrational modes of the phenyl rings dominate the SFG spectra at the PS/air interface as compared to the antisymmetric vibrational modes at the PS/sapphire interface. This indicates approximately parallel orientation of the phenyl rings at the PS/air interface while nearly perpendicular orientation at the PS/sapphire interface, with respect to the surface normal.

Aggregates of the diacid form of tetrakis(4-sulfonatophenyl)porphine (TPPS), formed in acidic aqueous solutions, were deposited onto hydrophilic (mica) and hydrophobic (polystyrene and graphite) substrates and imaged using atomic force microscopy (AFM). The AFM images revealed the aggregates were either individual rods with a diameter of 3.8 ± 0.3 nm and a length of 0.77 ± 0.43 μm or larger structures composed of bundles of individual rods. This study demonstrates that aggregates of the diacid form of TPPS are remarkably straight nanorods with a well-defined height. UV/vis spectroscopy and dynamic light-scattering measurements show that the aggregates form in solution and not on the surface of the substrate, with nucleation of the aggregates being the rate-limiting step, followed by rapid growth at the ends of the rods.

The photoconductivity of nanorods self-assembled from meso-tetrakis(4-sulfonatophenyl)porphine is described. The nanorods are insulating in the dark. Upon illumination with 488 nm light, the nanorods become photoconductive, exhibiting a rapid turn on/off (<100 ms) of the current when the light is turned on/off. This photoconductivity grows over hundreds of seconds with light exposure and decays slowly when the light is off. The nanorods can be trained via an applied bias to exhibit a short-circuit photocurrent (with corresponding open-circuit photovoltage) that flows in the direction opposite that of the training bias. A qualitative model is proposed, in which conduction occurs through the tightly coupled LUMOs of close-packed porphyrin molecules.