Photodriven Electron Transport within the Columnar Perylenediimide Nanostructures Self-Assembled with Sulfonated Porphyrins in Water

Columnar stacks of <i>N</i>,<i>N</i>′-di­(2-(trimethylammoniumiodide)­ethylene) perylenediimide (TAIPDI)_<i>n</i> can host <i>meso</i>-tetrakis­(4-sulfonatophenyl)­porphyrin zinc tetrapotassium salt (ZnTPPSK₄) molecules at different ratios through the ionic and π–π interactions prompted by an aqueous environment. Photoexcitation of this host–guest complex generates very fast charge separation (1.4 × 10¹² s^–1). Charge recombination is markedly decelerated by a probable electron delocalization mechanism along the long-range of tightly stacked TAIPDIs (4.6 × 10⁸ s^–1), giving an exceptional <i>k</i>_CS/<i>k</i>_CR ratio of 3000 as determined by using time-resolved transient absorption techniques

Characterization of Growth Patterns of Nanoscale Organic Films on Carbon Electrodes by Surface Enhanced Raman Spectroscopy

Electrochemical deposition of aromatic organic molecules by reduction of diazonium reagents enables formation of molecular layers with sufficient integrity for use in molecular electronic junctions of interest to microelectronics. Characterization of organic films with thicknesses in the 1–10 nm range is difficult with Raman spectroscopy, since most molecular structures of electronic interest have Raman cross sections which are too small to observe as either thin films on solid electrodes or within intact molecular junctions. Layer formation on a 10 nm thick Ag island film on a flat carbon surface (eC/Ag) permitted acquisition of structural information using surface enhanced Raman spectroscopy (SERS), in many cases for molecules with weak Raman scattering. Raman spectra obtained on eC/Ag surfaces were indistinguishable from those on carbon without Ag present, and the spectra of oligomeric molecular layers were completely consistent with those of the monomers. Layer growth was predominantly linear for cases where such growth was sterically allowed, and linear growth correlated strongly with the line width and splitting of the CC phenyl ring stretches. Molecular bilayers made by successive reduction of different diazonium reagents were also observable and will be valuable for applications of 1–20 nm organic films in molecular electronics

Broadband Light Harvesting and Fast Charge Separation in Ordered Self-Assemblies of Electron Donor–Acceptor-Functionalized Graphene Oxide Layers for Effective Solar Energy Conversion

Three-dimensionally (3D) ordered assemblies of GO layers functionalized with tetrakis­(1-methylpyridinium-4-yl)­porphyrin <i>p</i>-toluenesulfonate (Por), <i>N</i>,<i>N</i>′-di­(2-(trimethylammonium iodide)­ethylene) perylenediimide (PDI), and Zn­(II) phthalocyanine tetrasulfonic acid (ZnPc) were obtained in water. Proper molar ratio is essential between the cationic dyes, Por and PDI, acting as the “glue” molecules to combine the GO layers and the anionic ZnPc, acting as dispersant of GO layers to (i) construct the 3D assemblies and (ii) the proportional absorption distribution of dye-functionalized GO assemblies. Resulting 3D structures effectively harvest the light from ultraviolet to near-infrared (NIR) regions. Dye molecules are arranged in mainly lateral order on the GO layers with partial stacking, which allows direct interactions with the π-conjugations of the GO surface in 3D architecture. Ultrafast charge separation upon the photoexcitation of the dyes at various wavelengths in the visible/NIR region was observed in these assemblies, in which ZnPc and PDI were the ultimate electron donor and acceptor, respectively. Lateral charge migration among the partially stacked dye molecules was inferred from the decay characteristics of the radical ion pair. Triggered by the charge separation processes in the 3D ordered self-assemblies, significantly higher photocurrent density in the OTE/SnO₂ electrode deposited with self-assemblies of (GO–Por–PDI–ZnPc)_<i>n</i> was generated compared to those deposited with only GO or dye components