Nitrogen-doped polycyclic aromatic hydrocarbons by a one-pot Suzuki coupling/intramolecular SNArS_NAr reaction

We report a new method for the synthesis of nitrogen-doped (N-doped) polycyclic aromatic hydrocarbons (PAHs) by a Suzuki coupling/intramolecular S$_N$Ar cascade reaction. A one- or two-fold [3 + 3] naphtho-annulation of halogenated aniline was conducted under Suzuki–Miyaura cross-coupling conditions to yield a series of fully fused N-doped PAHs. In contrast to reported methods to synthesize pyridinic or pyrrolic nitrogen-doped PAHs, our method enables preparation of PAHs doped with graphitic nitrogen, for which few reports are known in the literature. The crystal structure as well as absorption, fluorescence and electrochemical properties of these N-doped PAHs were investigated, which demonstrated the capability of N-doping to adjust optical and electronic properties and alter the LUMO energy level

Structure-Property Relationships from Atomistic Multiscale Simulations of the Relevant Processes in Organic Solar Cells. I. Thermodynamic Aspects

Interface structures of a variety of molecular p-type semiconductors in heterojunction with fullerene C-60 were generated in molecular dynamic simulations. Using the dimer method (i.e., dimers were used as the quantum-mechanical system) along with a continuum salvation approach and macroscopic electric fields, energetic profiles of the interfaces of organic solar cells (OSCs) were calculated. Several important loss mechanisms, such as exciton trapping, charge trapping, and interfacial charge-transfer traps, were observed. Structure-property relationships were established. They reveal that apart from the molecular orientation and dipolarity, molecular size is an important parameter that influences potential loss mechanisms

Atomistic Approach To Simulate Processes Relevant for the Efficiencies of Organic Solar Cells as a Function of Molecular Properties. II. Kinetic Aspects

The individual steps of the light-to-energy conversion process in the vicinity of the interfaces of organic solar cells are investigated with kinetic Monte Carlo simulations employing Marcus hopping rates obtained from quantum-chemical calculations. A chemically diverse set of p-type semiconducting molecules in heterojunction with fullerene C-60 is used. Starting with exciton diffusion, exciton dissociation, charge generation, and charge separation are modeled on an atomistic level. Numerous aspects were already analyzed, but comprehensive simulations including all three processes in amorphous model interface systems and a comparison of various different molecular p-type semiconductors seem to be missing. Our investigation identifies several important kinetic effects that could limit device efficiencies, such as the strong reduction of charge transport rates in the vicinity of the interface due to Coulomb interactions between the charges, the importance of adjusting the relative rates of exciton transfer and dissociation, and the impact of morphology. Charge drift velocities and hole mobilities obtained from the simulations compare well with experimental values indicating that the main effects are covered by the simulations. A correlation between experimental short-circuit currents and simulated charge drift velocities suggests that slow charge-transfer processes could represent a major efficiency-limiting parameter in organic solar cells

C64_{64} Nanographene Tetraimide – A Receptor for Phthalocyanines with Subnanomolar Affinity

Phthalocyanines are extensively used by the dye and pigment industry and in photovoltaic and photodynamic therapy research due to their intense absorption of visible light, outstanding stability, and versatility. As pigments, the unsubstituted phthalocyanines are insoluble owing to strong intermolecular $π-π-$stacking interactions, which causes limitations for the solution chemistry for both free base and metalated phthalocyanines. Here we show a supramolecular host–guest strategy to dissolve phthalocyanines into solution. C$_{64}$ nanographene tetraimide (1) binds two free base/zinc/copper phthalocyanines in a 1 : 2 stoichiometry to solubilize phthalocyanines as evidenced by $^1$H NMR spectroscopy, UV/Vis absorption and single-crystal X-ray analysis. Binding studies using a tetra-tert-butyl-substituted soluble phthalocyanine revealed binding affinities of up to 10$^9$ M$^{−1}$ in tetrachloromethane, relating to a Gibbs free energy of −52 kJ mol$^{−1}$. Energy decomposition analysis revealed that complexes between 1 and phthalocyanines are stabilized by dispersion interactions followed by electrostatics as well as significant charge-transfer interactions

Fluorescence Enhancement by Supramolecular Sequestration of a C54C_{54} -Nanographene Trisimide by Hexabenzocoronene

A supramolecular trilayer nanographene complex consisting of a newly synthesized D3h-symmetric C54-nanographene trisimide (NTI 1) and two hexabenzocoronenes (HBC) has been obtained by self-assembly. This 1:2 complex is structurally well-defined according to UV/vis and single crystal X-ray studies and exhibits high thermodynamic stability even in polar halogenated solvents. Complexation of NTI 1 by two HBC molecules protects the NTI 1 π-surface efficiently from oxygen quenching, thereby leading to a sequestration-induced fluorescence enhancement under ambient conditions

Water-Soluble Cationic Perylene Diimide Dyes as Stable Photocatalysts for H2O2 Evolution

Photocatalytic generation of hydrogen peroxide, H2O2, has gained increasing attention in recent years, with applications ranging from solar energy conversion to biophysical research. While semiconducting solid-state materials are normally regarded as the workhorse for photogeneration of H2O2, an intriguing alternative for on-demand H2O2 is the use of photocatalytic organic dyes. Herein we report the use of water-soluble dyes based on perylene diimide molecules which behave as true molecular catalysts for the light-induced conversion of dissolved oxygen to hydrogen peroxide. In particular, we address how to obtain visible-light photocatalysts which are stable with respect to aggregation and photochemical degradation. We report on the factors affecting efficiency and stability, including variable electron donors, oxygen partial pressure, pH, and molecular catalyst structure. The result is a perylene diimide derivative with unprecedented peroxide evolution performance using a broad range of organic donor molecules and operating in a wide pH range.Funding Agencies|National Science Centre, Poland [2019/33/B/ST5/01212]; Bavarian State Ministry for Science and the Arts; European Research Council (ERC) under the European Union [949191, 787937]; city council of Brno, Czech Republic; Knut and Alice Wallenberg Foundation</p

12b,24b‐Diborahexabenzo[a,c,fg,l,n,qr]pentacene: A Low‐LUMO Boron‐Doped Polycyclic Aromatic Hydrocarbon

Herein we devise and execute a new synthesis of a pristine boron-doped nanographene. Our target boron-doped nanographene was designed based on DFT calculations to possess a low LUMO energy level and a narrow band gap derived from its precise geometry and B-doping arrangement. Our synthesis of this target, a doubly B-doped hexabenzopentacene (B$_2$-HBP), employs six net C−H borylations of an alkene, comprising consecutive hydroboration/electrophilic borylation/dehydrogenation and BBr$_3$/AlCl$_3$/2,6-dichloropyridine-mediated C−H borylation steps. As predicted by our calculations, B$_2$-HBP absorbs strongly in the visible region and emits in the NIR up to 1150 nm in o-dichlorobenzene solutions. Furthermore, B2-HBP possesses a very low LUMO level, showing two reversible reductions at −1.00 V and −1.17 V vs. Fc+/Fc. Our methodology is surprisingly selective despite its implementation of unfunctionalized precursors and offers a new approach to the synthesis of pristine B-doped polycyclic aromatic hydrocarbons

Organic Light‐Emitting Diodes Based on Silandiol‐Bay‐Bridged Perylene Bisimides

Perylene bisimides (PBIs) are among the best fluorophores but have to be enwrapped for optoelectronic applications by large and heavy substituents to prevent their ππ‐stacking, which is known to accelerate non‐radiative decay processes in the solid state. Here, light‐weight di‐tert‐butylsilyl groups are introduced to bridge 1,12‐dihydroxy and 1,6,7,12‐tetrahydroxy PBIs to afford sublimable dyes for vacuum‐processed optoelectronic devices. For both new compounds, this substitution provides a twisted and shielded perylene π‐core whose, via OSiObridges, rigid structure affords well‐resolved absorption and emission spectra with strong fluorescence in solution, as well as in the solid state. The usefulness of these dyes for vacuum‐processed optoelectronic devices is demonstrated in organic light‐emitting diodes (OLEDs) that show monomer‐like emission spectra and high maximum external quantum efficiency (EQEmax) values of up to 3.1% for the doubly silicon‐bridged PBI

Photoblinking dynamics in single calix[4]arene-linked perylene bisimide dimers

We have studied the fluorescence from individual bridge-linked perylene bisimide dimers and observed blinking over three decades in time which reveals a power-law distribution for the 'off' times. The time traces featured three distinct levels of intensity which we assign to the dimer, monomer and background level, respectively. Based on the chronological order of the occurence of the intensity levels we grouped the time traces into three categories and come to the conclusion that for one of these groups the blinking behaviour is governed by a mechanism that is reminiscent to Coulomb blockade in semiconductor quantum dots. (C) 2009 Elsevier B. V. All rights reserved

Folding‐Induced Promotion of Proton‐Coupled Electron Transfers via Proximal Base for Light‐Driven Water Oxidation

Proton‐coupled electron‐transfer (PCET) processes play a key role in biocatalytic energy conversion and storage, for example, photosynthesis or nitrogen fixation. Here, we report a series of bipyridine‐containing di‐ to tetranuclear Ru(bda) macrocycles 2 C–4 C (bda: 2,2′‐bipyridine‐6,6′‐dicarboxylate) to promote O−O bond formation. In photocatalytic water oxidation under neutral conditions, all complexes 2 C–4 C prevail in a folded conformation that support the water nucleophilic attack (WNA) pathway with remarkable turnover frequencies of up to 15.5 s$^{−1}$ per Ru unit respectively. Single‐crystal X‐ray analysis revealed an increased tendency for intramolecular π‐π stacking and preorganization of the proximal bases close to the active centers for the larger macrocycles. H/D kinetic isotope effect studies and electrochemical data demonstrate the key role of the proximal bipyridines as proton acceptors in lowering the activation barrier for the crucial nucleophilic attack of H$_{2}$O in the WNA mechanism