Positional Isomers of Chromophore-Peptide Conjugates Self-Assemble into Different Morphologies.

Ordering π-systems into defined supramolecular structures is important for the development of organic functional materials. In recent years, peptides with defined secondary structures and/or self-assembly properties were introduced as powerful tools to order peptide-chromophore conjugates into different morphologies. This work explores whether or not the directionality of peptides can be used to control the self-assembly. The position of the π-system in conjugates between oligoprolines and perylene monoimide (PMI) chromophores was varied by attaching the PMI moiety to the second-to-last residue from the C- and N-termini, respectively. Microscopic and diffraction analysis revealed that the positional isomers form distinctly different supramolecular architectures that extend into the micrometer regime. NMR spectroscopic studies in solution phase allowed correlation of the self-assembly properties with markedly different conformational preferences of the isomeric building blocks. These insights enabled the design of building blocks with predictable self-assembly properties. Thus, the directionality of peptides offers exciting opportunities for controlling the self-assembly and electronic properties of π-systems.

A triaxial supramolecular weave.

Despite recent advances in the synthesis of increasingly complex topologies at the molecular level, nano- and microscopic weaves have remained difficult to achieve. Only a few diaxial molecular weaves exist-these were achieved by templation with metals. Here, we present an extended triaxial supramolecular weave that consists of self-assembled organic threads. Each thread is formed by the self-assembly of a building block comprising a rigid oligoproline segment with two perylene-monoimide chromophores spaced at 18 Å. Upon π stacking of the chromophores, threads form that feature alternating up- and down-facing voids at regular distances. These voids accommodate incoming building blocks and establish crossing points through CH-π interactions on further assembly of the threads into a triaxial woven superstructure. The resulting micrometre-scale supramolecular weave proved to be more robust than non-woven self-assemblies of the same building block. The uniform hexagonal pores of the interwoven network were able to host iridium nanoparticles, which may be of interest for practical applications.

(o-Phenyleno)naphthalene diimides: a pink fluorescent chromophore.

(o-Phenyleno)naphthalene dianhydride 7 was synthesized by a six-step reaction. Imidizations of 7 led to various diimides 8. Their optical and electrochemical properties hold promise for organic electronics.

Enhanced Photocurrent Density by Spin-Coated NiO Photocathodes for N-Annulated Perylene-Based p-Type Dye-Sensitized Solar Cells.

The low photocurrent density of p-type dye-sensitized solar cells (p-DSSCs) has limited the development of high-efficiency tandem cells due to the inadequate light-harvesting ability of sensitizers and the low hole mobility of semiconductors. Hereby, two new "push-pull" type organic dyes (PQ-1 and PQ-2) containing N-annulated perylene as electron donor have been synthesized, where the PQ-2-based p-DSSCs show higher photoelectric conversion efficiency (PCE) of 0.316% owing to the higher molar extinction compared to of that PQ-1. Additionally, the photocurrent densities were remarkably increased from 2.20 to 5.85 mA cm(-2) for PQ-1 and 2.45 to 6.69 mA cm(-2) for PQ-2 by spin-coated NiO photocathode based-p-DSSCs, respectively. This results are ascribed to the enhancement of hole transport rate, dye-loading amounts and transparency of NiO films in comparison to that prepared by screen-printing method. Electrochemical impedance spectroscopy and theoretical calculations studies indicate that the molecular dipole moment approaching closer to the NiO surface shifts the quasi-Fermi level to more positive levels, improving open-circuit voltage (Voc). Intensity-modulated photocurrent spectroscopy illustrates that the hole transit time in NiO films prepared in spin-coating is shorter than that prepared by screen-printing method.

Synthesis, Ensemble, and Single Molecule Characterization of a Diphenyl-Acetylene Linked Terrylenediimide Dimer.

The synthesis and the photophysical characterization at the ensemble and single molecule level of a terrylenediimide (TDI) dimer are reported. The spectroscopic experimental data are compared with those obtained for the corresponding model compound TDI. Steady-state and ps time-correlated single photon counting have shown that both chromophores in the TDI dimer are in the weak coupling regime allowing their interaction by Förster resonance energy transfer. Femtosecond transient absorption experiments showed an excitation power dependence of the fluorescence decay, which could indicate the occurrence of singlet-singlet annihilation. Single molecule intensity traces were investigated for the TDI dimer and suggested two intensity levels. For both intensity levels several parameters among which emission maximum, fluorescence decay times, antibunching, blinking off-times and rate of dark state formation were compared. The blinking analysis revealed that the yield of dark state formation is an order of magnitude higher when the two chromophores are still active compared to the case where one is photobleached. The off-times remain however similar.

Photophysical investigation of cyano-substituted terrylenediimide derivatives.

Two new terrylenediimide (TDI) chromophores with cyano substituents in the bay and core area (BCN-TDI and OCN-TDI, respectively) have been characterized by a wide range of techniques, and their applicability for stimulated emission depletion (STED) microscopy has been tested. By cyano substitution an increase of the fluorescence quantum yield and a decrease of the nonradiative rate constant is achieved and attributed to a reduced charge-transfer character of the excited state due to a lower electron density of the TDI core. For BCN-TDI, the substitution in the bay area induces a strong torsional twist in the molecule which, similar to phenoxy bay-perylenediimide (PDI), has a strong effect on the fluorescence lifetime but appears to prevent the aggregation that is observed for OCN-TDI. The single-molecule photobleaching stability of BCN- and OCN-TDI is lower than that of a reference TDI without cyano substitution (C7-TDI), although less so for OCN-TDI. The photophysical properties of the excited singlet state are only slightly influenced by the cyano groups. The observed intense stimulated emission, the pump-dump-probe experiments, and STED single-molecule imaging indicate that STED experiments with the cyano-substituted TDIs are possible. However, because of aggregation and more efficient photobleaching, the performance of BCN- and OCN-TDI is worse than that of the reference compound without cyano groups (C7-TDI). Bay-substituted TDIs are less suitable for STED microscopy.

Green emitting photoproducts from terrylene diimide after red illumination.

The spectral properties of emissive photoproducts, formed upon 633 nm irradiation of a terrylene diimide dye, were investigated. Ensemble and single-molecule level experiments were conducted by immobilizing the TDI dye molecules in a polystyrene film. In the bulk experiments, green emission could be observed from the photobleached areas (photobleached with 633 nm light) when excited with 480 or 514 nm light. Similar phenomena were also observed at the single-molecule level. On the basis of the single-molecule experiments, a conversion efficiency of about 5% was estimated for the formation of emissive spectrally blue-shifted photoproducts. These green emissive photoproducts have spectral properties that resemble those of lower rylene homologues, e.g. perylene diimide or perylene monoimide. Our results indicate that the formation of blue-shifted emissive photoproducts can have implications for analyzing single-molecule FRET experiments or multiple color-labeled fluorescent systems.