Self-Assembly of 9,10-Bis(phenylethynyl) anthracene (BPEA) Derivatives: Influence of pi-pi and Hydrogen Bonding Interactions on Aggregate Morphology and Self-Assembly Mechanism

9,10-Bis(phenylethynyl)anthracenes (BPEAs) are an important class of dyes with various applications including chemiluminescence emitters, materials for photon upconversion and for optoelectronic devices. Some of these applications require control over the packing modes of the active molecules within the active layer, which can be effected by bottom-up self-assembly. Studies aimed at controlling the molecular organization of BPEAs have primarily focused on bulk or liquid crystal materials, while in-depth investigations of BPEA-based assemblies in solution remain elusive. In this article, we report the self-assembly of two new BPEA derivatives with hydrophobic side chains, one of them featuring amide functional groups (2) and the other one lacking them (1). Comparison of the self-assembly behaviour in solution of both systems via spectroscopic (UV/Vis, fluorescence and NMR), microscopic (AFM) and theoretical (PM6) studies reveals the crucial role of the amide groups in controlling the self-assembly. While for both systems the formation of H-type face-to-face -stacks is proposed, the interplay of -stacking and H-bonding is responsible of driving the formation of 1D stacks and increasing the binding constant two-to-three orders of magnitude. Our findings show that H-bonding is a prerequisite to create ordered BPEA assemblies in solution

Zinc Phthalocyanine−Graphene Hybrid Material for Energy Conversion: Synthesis, Characterization, Photophysics and Photoelectrochemical Cell Preparation

Graphene exfoliation upon tip sonication in o-­‐DCB was accomplished. Then, covalent grafting of (2-­‐ aminoethoxy)(tri-­‐tert-­‐butyl) zinc phthalocyanine (ZnPc), to exfoliated graphene sheets was achieved. The newly formed ZnPc-­‐graphene hybrid material was found soluble in common organic solvents without any precipitation for several weeks. Application of diverse spectroscopic techniques verified the successful formation of ZnPc-­‐graphene hybrid materi-­‐ al, while thermogravimetric analysis revealed the amount of ZnPc loading onto graphene. Microscopy analysis based on AFM and TEM was applied to probe the morphological characteristics and to investigate the exfoliation of graphene sheets. Efficient fluorescence quenching of ZnPc in the ZnPc-­‐graphene hybrid material suggested that photoinduced events occur from the photoexcited ZnPc to exfoliated graphene. The dynamics of the photoinduced electron transfer was evaluated by femtosecond transient absorption spectroscopy, thus, revealing the formation of transient species such as ZnPc+ yielding the charge-­‐separated state ZnPc•+–graphene•–. Finally, the ZnPc-­‐graphene hybrid material was integrated into a photoactive electrode of an optical transparent electrode (OTE) cast with nanostructured SnO2 films (OTE/SnO2), which exhibited sta le and reproducible photocurrent responses and the incident photon-­‐to-­‐current conversion efficien-­‐ cy was determine

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

Creation of superheterojunction polymers via direct polycondensation: segregated and bicontinuous donor–acceptor π-columnar arrays in covalent organic frameworks for long-lived charge separation

By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor–acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor π-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic π-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctionsa new type of heterojunction machinery, for photoinduced electron transfer and charge separation. We show that this polycondensation method is widely applicable to various metallophthalocyanines and diimides as demonstrated by the combination of copper, nickel, and zinc phthalocyanine donors with pyrommellitic diimide, naphthalene diimide, and perylene diimide acceptors. By using time-resolved transient absorption spectroscopy and electron spin resonance, we demonstrated that the COFs enable long-lived charge separation, whereas the metal species, the class of acceptors, and the local geometry between donor and acceptor units play roles in determining the photochemical dynamics. The results provide insights into photoelectric COFs and demonstrate their enormous potential for charge separation and photoenergy conversions