Four-Step Domino Reaction Enables Fully Controlled Non-Statistical Synthesis of Hexaarylbenzene with Six Different Aryl Groups*

Hexaarylbenzene (HAB) derivatives are versatile aromatic systems playing a significant role as chromophores, liquid crystalline materials, molecular receptors, molecular-scale devices, organic light-emitting diodes and candidates for organic electronics. Statistical synthesis of simple symmetrical HABs is known via cyclotrimerization or Diels–Alder reactions. By contrast, the synthesis of more complex, asymmetrical systems, and without involvement of statistical steps, remains an unsolved problem. Here we present a generally applicable synthetic strategy to access asymmetrical HAB via an atom-economical and high-yielding metal-free four-step domino reaction using nitrostyrenes and α,α-dicyanoolefins as easily available starting materials. Resulting domino product—functionalized triarylbenzene (TAB)—can be used as a key starting compound to furnish asymmetrically substituted hexaarylbenzenes in high overall yield and without involvement of statistical steps. This straightforward domino process represents a distinct approach to create diverse and still unexplored HAB scaffolds, containing six different aromatic rings around central benzene core. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH Gmb

Integrating metalloporphycenes into p-type NiO-based dye-sensitized solar cells

In the current work, we have explored a novel synthetic route towards metalated porphycenes and their use in p-type NiO-based dye-sensitized solar cells. Particular emphasis is placed on the influence that the relative positioning of the anchoring group exerts on the DSSC performance

Oxidative Cyclodehydrogenation Reactions with Tetraarylporphyrins

The extension of the aromatic π‐system of porphyrins is a powerful method to alter their optoelectronic properties. Herein, aryl substituents were fused to porphyrin cores by Scholl oxidation reactions that selectively produced mono‐ and doubly‐fused porphyrins in yields of up to 69 %. Several different aryl substituents attached to the porphyrin were investigated with respect to their reactivity under Scholl conditions. The fused products were fully characterized, i.e., by UV/Vis absorption spectroscopy, which showed drastic changes in the electronic features. Insight into the solid‐state behavior was obtained by X‐ray crystallography. Our approach represents a novel option for the late‐stage functionalization of porphyrin‐based compounds

Making the invisible visible: improved electrospray ion formation of metalloporphyrins/-phthalocyanines by attachment of the formate anion (HCOO-)

A protocol is developed for the coordination of the formate anion (HCOO-) to neutral metalloporphyrins (Pors) and -phthalocyanines (Pcs) containing divalent metals as a means to improve their ion formation in electrospray ionization (ESI). This method is particularly useful when the oxidation of the neutral metallomacrocycle fails. While focusing on Zn(II)Pors and Zn(II)Pcs, we show that formate is also readily attached to Mn(II), Mg(II) and Co(II)Pcs. However, for the Co(II)Pc secondary reactions can be observed. Upon collision-induced dissociation (CID), Zn(II)Por/Pc·formate supramolecular complexes can undergo the loss of CO2 in combination with transfer of a hydride anion (H-) to the zinc metal center. Further dissociation leads to electron transfer and hydrogen atom loss, generating a route to the radical anion of the Zn(II)Por/Pc without the need for electrochemical reduction, although the Zn(II)Por/Pc may have a too low electron affinity to allow electron transfer directly from the formate anion. In addition to single Por molecules, multi Por arrays were successfully analyzed by this method. In this case, multiple addition of formate occurs, giving rise to multiply charged species. In these multi Por arrays, complexation of the formate anion occurs by two surrounding Por units (sandwich). Therefore, the maximum attainment of formate anions in these arrays corresponds to the number of such sandwich complexes rather than the number of porphyrin moieties. The same bonding motif leads to dimers of the composition [(Zn(II)Por/Pc)2·HCOO]-. In these, the formate anion can act as a structural probe, allowing the distinction of isomeric ions with the formate bridging two macrocycles or being attached to a dimer of directly connected macrocycles.Financial support from the Deutsche Forschungsgemeinschaft (DFG)-SFB 953 “Synthetic Carbon Allotropes”, the MINECO, Spain (CTQ-2014-52869-P) and the Comunidad de Madrid (S2013/MIT-2841 FOTOCARBON, T.T.) is acknowledged

Synthesis and first X-ray structure of a hexa-peri-hexabenzocoronene–fullerene-dyad: a model for an inter-carbon-allotrope hybrid

The synthesis of a new hexa-peri-hexabenzocoronene (HBC)–fullerene dyad 1 was accomplished involving a covalent linkage between both the planar and the spherical conjugated π-system of the two chromophores. We also present the first X-ray single crystal structure of a HBC–fullerene conjugate. A very short HBC–fullerene distance of 3.2 Å is observed. For the synthesis of this molecule, a new versatile applicable template, namely, a mono-functionalized hexa-peri-hexabenzocoronene 7 was attached to a fullerene. Absorption and fluorescence spectroscopy, as well as quantum yield measurements of 1, indicated close electronic communication between the two subunits, which is promising for possible applications in molecular electronics

Wet-Chemically Prepared Porphyrin Layers on Rutile TiO2(110)

Porphyrins are large organic molecules that are interesting for different applications, such as photovoltaic cells, gas sensors, or in catalysis. For many of these applications, the interactions between adsorbed molecules and surfaces play a crucial role. Studies of porphyrins on surfaces typically fall into one of two groups: (1) evaporation onto well-defined single-crystal surfaces under well-controlled ultrahigh vacuum conditions or (2) more application-oriented wet chemical deposition onto less well-defined high surface area surfaces under ambient conditions. In this study, we will investigate the wet chemical deposition of 5-(monocarboxyphenyl)-10,15,20-triphenylporphyrin (MCTPP) on well-defined rutile TiO2 (110) single crystals under ambient conditions. Prior to deposition, the TiO2(110) crystals were also cleaned wet-chemically under ambient conditions, meaning none of the preparation steps were done in ultrahigh vacuum. However, after each preparation step, the surfaces were characterized in ultrahigh vacuum with X-ray photoelectron spectroscopy (XPS) and the result was compared with porphyrin layers prepared in ultrahigh vacuum (UHV) by evaporation. The differences of both preparations when exposed to zinc ion solutions will also be discussed.Fil: Wechsler, Daniel. Universitat Erlangen-Nuremberg; AlemaniaFil: Fernández, Cynthia Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Köbl, Julia. Universitat Erlangen-Nuremberg; AlemaniaFil: Augustin, Lisa Marie. Universitat Erlangen-Nuremberg; AlemaniaFil: Stumm, Corina. Universitat Erlangen-Nuremberg; AlemaniaFil: Norbert Jux. Universitat Erlangen-Nuremberg; AlemaniaFil: Steinruck, Hans Peter. Universitat Erlangen-Nuremberg; AlemaniaFil: Williams, Federico José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Lytken, Ole. Universitat Erlangen-Nuremberg; Alemani

A Functional Hexaphenylbenzene Library Comprising of One, Three, and Six Peripheral Rylene‐Diimide Substituents

Abstract Synthesis and characterization of a series of rylene‐diimide substituted hexaphenylbenzenes (HPBs) is presented. The direct connection of the rylene‐diimide units to the HPBs via the imide‐N‐position without any linkers as well as the use of naphthalene‐diimides (NDIs) next to perylene‐diimides (PDIs) is unprecedented. While mono‐substituted products were obtained by imidization reactions with amino‐HPB and the respective rylene‐monoimides, key step for the formation of tri‐ and hexa‐substituted HPBs is the Co‐catalysed cyclotrimerization. Particular emphasis for physic‐chemical characterization was on to the number of NDIs/PDIs per HPB and the overall substitution patterns. Lastly, Scholl oxidation conditions were applied to all HPB systems to generate the corresponding hexa‐peri‐hexabenzocoronenes (HBCs). Importantly, the efficiency of the transformation strongly depends on the number of NDIs/PDIs. While three rylene‐diimide units already hinder the Scholl reaction, the successful synthesis of mono‐substituted HBCs is possible

Structure and Conformation of Individual Molecules upon Adsorption of a Mixture of Benzoporphyrins on Ag(111), Cu(111), and Cu(110) Surfaces

We investigated the adsorption behavior of a mixture of six 2H‐tetrakis‐(3, 5‐di‐tert‐butylphenyl)(x)benzoporphyrins (2H‐diTTBP(x)BPs, x=0, 1, 2‐cis, 2‐trans, 3, and 4) on Ag(111), Cu(111) and Cu(110) at room temperature by scanning tunneling microscopy (STM) under ultra‐high vacuum conditions. On Ag(111), we observe an ordered two‐dimensional square phase, which is stable up to 400 K. On Cu(111), the same square phase coexists with a stripe phase, which disappears at 400 K. In contrast, on Cu(110), 2H‐diTTBP(x)BPs adsorb as immobile isolated molecules or dispersed short chains along the [1 1‾ ${\bar{1}}$ 0] substrate direction, which remain intact up to 450 K. The stabilization of the 2D supramolecular structures on Ag(111) and Cu(111), and of the 1D short chains on Cu(110) is attributed to van der Waals interactions between the tert‐butyl and phenyl groups of neighboring molecules. From high‐resolution STM, we can assign all six 2H‐diTTBP(x)BPs within the ordered structures. Moreover, we deduce a crown shape quadratic conformation on Ag(111) and Cu(111), an additional saddle‐shape on Cu(111), and an inverted structure and a quadratic appearance on Cu(110). The different conformations are attributed to the different degree of interaction of the iminic nitrogen atoms of the isoindole and pyrrole groups with the substrate atoms.A mixture of six 2H‐tetrakis‐(3, 5‐di‐tert‐butylphenyl)(x)benzoporphyrins (2H‐diTTBP(x)BPs, x=0, 1, 2‐cis, 2‐trans, 3, and 4) on Ag(111) as observed in high‐resolution scanning tunneling microscopy at room temperature. image German Research Foundation http://dx.doi.org/10.13039/501100001659Friedrich-Alexander-Universität Erlangen-NürnbergTU Dresden http://dx.doi.org/10.13039/50110000295

Self-assembly and coverage dependent thermally induced conformational changes of Ni(II)-meso-tetrakis (4-tert-butylphenyl) benzoporphyrin on Cu(111)

A systematic scanning tunnelling microscopy investigation of the self-assembly and of thermally induced conformational changes of Ni(II)-meso-tetrakis (4-tert-butylphenyl) benzoporphyrin (Ni-TTBPBP) on Cu(111) is presented. At room temperature, Ni-TTBPBPs diffuse on the surface and self-assemble into ordered islands with well-defined registry to the substrate, with two different azimuthal orientations. The formation of the characteristic supramolecular structure is attributed to van der Waals interactions between the tert-butyl groups. Upon moderate heating, the intramolecular conformation changes irreversibly due to a dehydrogenative intramolecular aryl–aryl coupling reaction. This reaction is coverage dependent, with a lower rate at higher initial coverage; this behaviour is attributed to a stabilization of Ni-TTBPBP in the ordered islands at higher coverage

[18]Annulene put into a new perspective

New insights into [18]annulene were gained by looking more closely at its X-ray structure, revealing a close face-to-face stacking of 3.16 Å in a herringbone-like crystal packing. Hexadehydro[18]annulene was co-crystalized in a benzene matrix, demonstrating the stabilizing role of intercalated solvent molecules in solid annulenes