Characterization of designed cobaltacarborane porphyrins using conductive probe atomic force microscopy

© 2016 Jayne C. Garno, et al. Porphyrins and metalloporphyrins have unique chemical and electronic properties and thus provide useful model structures for studies of nanoscale electronic properties. The rigid planar structures and π-conjugated backbones of porphyrins convey robust electrical characteristics. For our investigations, cobaltacarborane porphyrins were synthesized using a ring-opening zwitterionic reaction to produce isomers with selected arrangements of carborane clusters on each macrocycle. Experiments were designed to investigate how the molecular structure influences the selforganization, surface assembly, and conductive properties of three molecular structures with 2, 4, or 8 cobaltacarborane substituents. Current versus voltage (I-V) spectra for designed cobaltacarborane porphyrins deposited on conductive gold substrates were acquired using conductive probe atomic force microscopy (CP-AFM). Characterizations with CP-AFM provide capabilities for obtaining physical measurements and structural information with unprecedented sensitivity. We found that the morphology of cobaltacarborane porphyrin structures formed on surfaces depends on a complex interplay of factors such as the solvent used for dissolution, the nature of the substrate, and the design of the parent molecule. The conductive properties of cobaltacarborane porphyrins were observed to change according to the arrangement of cobaltacarborane substituents. Specifically, the number and placement of the cobaltacarborane ligands on the porphyrin macrocycle affect the interactions that drive porphyrin self-assembly and crystallization. Interestingly, coulombic staircase I-V profiles were detected for a porphyrin with two cobaltacarborane substituents

Solvent-Responsive Properties of Octadecyltrichlorosiloxane Nanostructures Investigated Using Atomic Force Microscopy in Liquid

An emerging challenge for nanoscale measurements is to capture and quantify the magnitude of structural changes in response to environmental changes. Certain environmental parameters can affect the nanoscale morphology of samples, such as changing the pH, solvent polarity, ionic strength, and temperature. We prepared test platforms of <i>n</i>-octadecyltrichlorosilane ring nanostructures to study surface morphology changes at the nanoscale in selected liquid media compared to dry conditions in air. Particle lithography combined with organosilane vapor deposition was used to fabricate nanostructures of regular dimensions. Multilayer nanostructures of OTS were used as a test platform for scanning probe studies of solvent-responsive properties where the sides of designed ring structures expose a 3D interface for studying the interaction of solvents with molecular side groups. In dry, ambient conditions, nanostructures of OTS were first imaged using contact mode atomic force microscopy (AFM). Next, ethanol or buffer was introduced to the sample cell, and images were acquired using the same probe. We observed substantial changes in the lateral and vertical dimensions of the ring nanostructures in AFM topography frames; the sizes of the rings were observed to swell by tens of nanometers. Even after heat treatment of samples to promote cross-linking, the samples still evidenced swelling in liquid media. This research will have consequences for studies of the properties of nanomaterials, such as solvent-responsive organic films and polymers

Solvent-Responsive Properties of Octadecyltrichlorosiloxane Nanostructures Investigated Using Atomic Force Microscopy in Liquid

An emerging challenge for nanoscale measurements is to capture and quantify the magnitude of structural changes in response to environmental changes. Certain environmental parameters can affect the nanoscale morphology of samples, such as changing the pH, solvent polarity, ionic strength, and temperature. We prepared test platforms of n-octadecyltrichlorosilane ring nanostructures to study surface morphology changes at the nanoscale in selected liquid media compared to dry conditions in air. Particle lithography combined with organosilane vapor deposition was used to fabricate nanostructures of regular dimensions. Multilayer nanostructures of OTS were used as a test platform for scanning probe studies of solvent-responsive properties where the sides of designed ring structures expose a 3D interface for studying the interaction of solvents with molecular side groups. In dry, ambient conditions, nanostructures of OTS were first imaged using contact mode atomic force microscopy (AFM). Next, ethanol or buffer was introduced to the sample cell, and images were acquired using the same probe. We observed substantial changes in the lateral and vertical dimensions of the ring nanostructures in AFM topography frames; the sizes of the rings were observed to swell by tens of nanometers. Even after heat treatment of samples to promote cross-linking, the samples still evidenced swelling in liquid media. This research will have consequences for studies of the properties of nanomaterials, such as solvent-responsive organic films and polymers. © 2014 American Chemical Society