David Schmidt

Influence of Solid-State Packing of Dipolar Merocyanine Dyes on Transistor and Solar Cell Performances

A series of nine dipolar merocyanine dyes has been studied as organic semiconductors in transistors and solar cells. These dyes exhibited single-crystal packing motifs with different dimensional ordering, which can be correlated to the performance of the studied devices. Hereby, the long-range ordering of the dyes in staircase-like slipped stacks with J-type excitonic coupling favors charge transport and improves solar cell performance. The different morphologies of transistor thin films and solar cell active layers were investigated by UV-vis, AFM, and XRD experiments. Selenium-containing donor-acceptor (D-A) dimethine dye 4 showed the highest hole mobility of 0.08 cm(2) V(-1) s(-1). BHJ solar cells based on dye 4 were optimized by taking advantage of the high crystallinity of the donor material and afforded a PCE of up to 6.2%.

Perylene Bisimide Radicals and Biradicals: Synthesis and Molecular Properties

Unprecedented neutral perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) radicals and biradicals were synthesized by facile chemical oxidation of 4-hydroxyaryl-substituted PBIs. Subsequent characterization by optical and magnetic spectroscopic techniques, as well as quantum chemical calculations, revealed an open-shell singlet biradical ground state for the PBI biradical OS-2(..) (〈s(2)〉=1.2191) with a relatively small singlet-triplet energy gap of 0.041 eV and a large singlet biradical character of y=0.72.

Ambient Stable Zwitterionic Perylene Bisimide‐Centered Radical

The unexpected introduction of a cationic imidazolium substituent in the 2-position of a tetrachloro-substituted perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) by the reaction of PBI-Cl4 1 with the N-heterocyclic carbene 1,3-di-iso-propyl-imidazolin-2-ylidene ((i)Pr2Im 2) enables the isolation of an ambient stable zwitterionic radical. The remarkable stability of this unprecedented PBI-centered radical facilitates the complete characterization by several spectroscopic methods as well as single crystal structure analysis. Redox studies revealed that (i)Pr2Im-PBI-Cl4 4 can be transferred reversibly to the corresponding anion and cation, respectively, even on a preparative scale.

An Electron-Poor C64 Nanographene by Palladium-Catalyzed Cascade C-C Bond Formation: One-Pot Synthesis and Single-Crystal Structure Analysis.

Abstract Herein, we report the one‐pot synthesis of an electron‐poor nanographene containing dicarboximide groups at the corners. We efficiently combined palladium‐catalyzed Suzuki–Miyaura cross‐coupling and dehydrohalogenation to synthesize an extended two‐dimensional π‐scaffold of defined size in a single chemical operation starting from N‐(2,6‐diisopropylphenyl)‐4,5‐dibromo‐1,8‐naphthalimide and a tetrasubstituted pyrene boronic acid ester as readily accessible starting materials. The reaction of these precursors under the conditions commonly used for Suzuki–Miyaura cross‐coupling afforded a C64 nanographene through the formation of ten C−C bonds in a one‐pot process. Single‐crystal X‐ray analysis unequivocally confirmed the structure of this unique extended aromatic molecule with a planar geometry. The optical and electrochemical properties of this largest ever synthesized planar electron‐poor nanographene skeleton were also analyzed.

Structural and quantum chemical analysis of exciton coupling in homo- and heteroaggregate stacks of merocyanines

Exciton coupling is of fundamental importance and determines functional properties of organic dyes in (opto-)electronic and photovoltaic devices. Here we show that strong exciton coupling is not limited to the situation of equal chromophores as often assumed. Quadruple dye stacks were obtained from two bis(merocyanine) dyes with same or different chromophores, respectively, which dimerize in less-polar solvents resulting in the respective homo- and heteroaggregates. The structures of the quadruple dye stacks were assigned by NMR techniques and unambiguously confirmed by single-crystal X-ray analysis. The heteroaggregate stack formed from the bis(merocyanine) bearing two different chromophores exhibits remarkably different ultraviolet/vis absorption bands compared with those of the homoaggregate of the bis(merocyanine) comprising two identical chromophores. Quantum chemical analysis based on an extension of Kashas exciton theory appropriately describes the absorption properties of both types of stacks revealing strong exciton coupling also between different chromophores within the heteroaggregate.

A cross-coupling-annulation cascade from peri-dibromonaphthalimide to pseudo-rylene bisimides

Herein we report a synthetic method to annulate naphthalimide moieties at different positions of a pyrene core by a cascade reaction involving palladium-mediated Suzuki–Miyaura cross-coupling and direct C–H arylation affording a new class of rylene bisimides, which we term as pseudo-rylene bisimides. The Pd-mediated reactions of peri-dibromonaphthalimide and pyrene boronic acid esters lead exclusively to six-membered ring annulation by a cascade C–C bond formation, for which a mechanistic rationale is proposed. Depending on the molecular geometry of the new pseudo-rylene bisimides, their optical properties resemble those of zethrene or terrylene bisimides, or polycyclic aromatic hydrocarbons like coronenes. The structural integrity of this new type of pseudo-rylene bisimides was confirmed by single crystal X-ray analysis.

Three-Dimensional Metal–Fullerene Frameworks

Hexakis-substituted [60]fullerene adducts with icosahedral symmetry provide an unprecedented scaffold for the spatial arrangement of twelve functional groups with high geometric precision. This unique molecular symmetry identifies such polyfunctional organic building blocks as potential highly connective linkers for coordination polymer and metal-organic framework synthesis. Hereby, the linker exhibits a higher connectivity than the metal ions and with the main connectivity based on the ligand, this can create a new type of inversely cross-linked framework. Two hexakis adducts bearing either twelve glycolic acid or 3-hydroxypropionic acid side chains attached to its malonate units were incorporated as organic connectivity centers in the first fullerene-containing three-dimensional frameworks by coordination with Zn(2+) .

Generic wound signals initiate regeneration in missing-tissue contexts

Despite the identification of numerous regulators of regeneration in different animal models, a fundamental question remains: why do some wounds trigger the full regeneration of lost body parts, whereas others resolve by mere healing? By selectively inhibiting regeneration initiation, but not the formation of a wound epidermis, here we create headless planarians and finless zebrafish. Strikingly, in both missing-tissue contexts, injuries that normally do not trigger regeneration activate complete restoration of heads and fin rays. Our results demonstrate that generic wound signals have regeneration-inducing power. However, they are interpreted as regeneration triggers only in a permissive tissue context: when body parts are missing, or when tissue-resident polarity signals, such as Wnt activity in planarians, are modified. Hence, the ability to decode generic wound-induced signals as regeneration-initiating cues may be the crucial difference that distinguishes animals that regenerate from those that cannot.Some wounds trigger regeneration, while others simply heal but how this is regulated is unclear. Here, by manipulating ERK and Wnt signalling pathways, the authors create headless planarians and finless zebrafish and show that wounds that normally only trigger wound healing can activate regeneration of heads and bones.

Library of Azabenz-Annulated Core-Extended Perylene Derivatives with Diverse Substitution Patterns and Tunable Electronic and Optical Properties

Here, we present a collection of different azabenz-annulated perylene derivatives. By developing new synthetic strategies and improving existing protocols, we have expanded the structural diversity of these dye molecules to a multifunctional class of ligating chromophores. The Pictet-Spengler (PS) reaction of 1-amino-perylenes with different aldehydes is used to modify the terminal substitution pattern. PS transformations of 1,6- and/or 1,7-diamino perylenes result in 2-fold annulated nitrogen-containing coronene-type molecules like anti-(ab)2-PBI 15, syn-(ab)2-PBI 16, and syn-(ab)2-PTE 18. In addition, azabenz-annulated perylene bisanhydrides (ab-PBA 6 and syn-(ab)2-PBA 19) were explored as universal starting materials providing access to any desired imide functionality. Furthermore, a newly developed regioselective nitration procedure for perylene monoimide diesters (PMIDE) enables the synthesis of 1-nitro-PMIDE 10 and thus of azabenz-annulated perylene derivatives with unsymmetric peri-substitution patterns (ab-PMIDE 12 and ab-PMIMA 13). According to our spectroscopic and theoretical investigations, the optical and electrochemical properties of these multifunctional chromophores can easily be modified and adjusted to many desirable applications following the synthetic strategies presented in this work.

Metal-Based Diversity for Crystalline Metal-Fullerene Frameworks

Four different three-dimensional metal-fullerene frameworks were synthesized through polymerization of two C60 -derived dodecaacids with varying alkyl spacers in the presence of Ca2+ , Cu2+ or Cd2+ ions. Structural analysis of the frameworks was performed by single-crystal X-ray diffraction and porosity of the materials was investigated by sorption measurements.