Alternating oligo(o,p-phenylenes) via ruthenium catalyzed diol-diene benzannulation: orthogonality to cross-coupling enables de novo nanographene and PAH construction

Transformation of Crowded Oligoarylene into Perylene-Cored Chiral Nanographene by Sequential Oxidative Cyclization and 1,2-Phenyl Migration

Synthetic innovation for constructing sophisticated nanographenes is of fundamental significance for a variety of advanced applications. Herein, we report a distinctive method to prepare π-extended chiral nanographenes with 29 benzenoid rings and two helical breaches from a highly crowded perylene-cored oligoarylene precursor. Under Scholl's conditions, the reaction predominantly involves the regioselective and sequential cyclization in the peri- and bay regions of the perylene core, and the complanation of the 1-phenyl[5]helicene intermediate module via 1,2-phenyl migration. The resulting chiral nanographenes are configurationally stable at 180 °C due to the high diastereomerization barriers of ca. 45 kcal mol^-1 . These molecules also possess globally delocalized π-systems with low HOMO/LUMO gaps, leading to nearly panchromatic absorption, intensive electronic circular dichroism signals and deep-red circularly polarized luminescence.

Chemical Tuning of Exciton versus Charge-Transfer Excited States in Conformationally Restricted Arylene Cages

Covalent assemblies of conjugated organic chromophores provide the opportunity to engineer new excited states with novel properties. In this work, a newly developed triple-stranded cage architecture, in which meta-substituted aromatic caps serve as covalent linking groups that attach to both top and bottom of the conjugated molecule walls, is used to tune the properties of thiophene oligomer assemblies. Benzene-capped and triazine-capped 5,5'-(2,2-bithiophene)-containing arylene cages are synthesized and characterized using steady-state and time-resolved spectroscopic methods. The conformational freedom and electronic states are analyzed using time-dependent density functional theory. The benzene cap acts as a passive spacer whose electronic states do not mix with those of the chromophore walls. The excited state properties are dominated by through-space interactions between the chromophore subunits, generating a neutral Frenkel H-type exciton state. This excitonic state undergoes intersystem crossing on a 200 ps time scale while the fluorescence output is suppressed by a factor of 2 due to a decreased radiative rate. Switching to a triazine cap enables electron transfer from the chromophore-linker after the initial excitation to the exciton state, leading to the formation of a charge-transfer state within 10 ps. This state can avoid intersystem crossing and exhibits red-shifted fluorescence with enhanced quantum yield. The ability to interchange structural modules with different electronic properties while retaining the overall cage morphology provides a new approach for tuning the properties of discrete chromophore assemblies.

Ruthenium-Catalyzed Cycloadditions to Form Five-, Six-, and Seven-Membered Rings

Ruthenium-catalyzed cycloadditions to form five-, six-, and seven-membered rings are summarized, including applications in natural product total synthesis. Content is organized by ring size and reaction type. Coverage is limited to processes that involve formation of at least one C-C bond. Processes that are stoichiometric in ruthenium or exploit ruthenium as a Lewis acid (without intervention of organometallic intermediates), ring formations that occur through dehydrogenative condensation-reduction, σ-bond activation-initiated annulations that do not result in net reduction of bond multiplicity, and photochemically promoted ruthenium-catalyzed cycloadditions are not covered.

Synthesis of some new distyrylbenzene derivatives using immobilized Pd on an NHC-functionalized MIL-101(Cr) catalyst: photophysical property evaluation, DFT and TD-DFT calculations

In this study the catalytic application of a heterogeneous Pd-catalyst system based on metal organic framework [Pd-NHC-MIL-101(Cr)] was investigated in the synthesis of distyrylbenzene derivatives using the Heck reaction. The Pd-NHC-MIL-101(Cr) catalyst showed high efficiency in the synthesis of these π-conjugated materials and products were obtained in high yields with low Pd-contamination based on ICP analysis. The photophysical behaviors for some of the synthesized distyrylbenzene derivatives were evaluated. The DFT and TD-DFT methods were employed to determine the optimized molecular geometry, band gap energy, and the electronic absorption and emission wavelengths of the new synthesized donor-π-acceptor (D-π-A) molecules in the gas phase and in various solvents using the chemical model B3LYP/6-31+G(d,p) level of theory.

Synthesis and Photophysical Properties of Soluble N-Doped Rubicenes via Ruthenium-Catalyzed Transfer Hydrogenative Benzannulation

Ruthenium-catalyzed butadiene-mediated benzannulation enabled the first synthesis of 3,10-(di-tert-butyl)rubicene and its N-doped derivatives as well as preliminary studies on their photophysical properties. Unlike the parent rubicene and 3,10-(di-tert-butyl)rubicene, which adopt classical herringbone-type packing motifs in the solid state, the N-doped congener 7 b displayed columnar packing with an alternating co-facial arrangement of aromatic and heteroaromatic substructures.

Benzannulation through Ruthenium(0)-Catalyzed Transfer Hydrogenative Cycloaddition: Precision Synthesis and Photophysical Characterization of Soluble Diindenoperylenes

The first application of ruthenium(0)-catalyzed 1,2-dione-diyne [2+2+2] cycloaddition to PAH construction is achieved by the precision synthesis of soluble diindenoperylenes (DIPs), the electronic structures of which were investigated using steady-state absorption and emission, transient absorption, cyclic voltammetry and time-dependent density functional theory.

Synthetic Applications of Oxidative Aromatic Coupling-From Biphenols to Nanographenes

Oxidative aromatic coupling occupies a fundamental place in the modern chemistry of aromatic compounds. It is a method of choice for the assembly of large and bewildering architectures. Considerable effort was also devoted to applications of the Scholl reaction for the synthesis of chiral biphenols and natural products. The ability to form biaryl linkages without any prefunctionalization provides an efficient pathway to many complex structures. Although the chemistry of this process is only now becoming fully understood, this reaction continues to both fascinate and challenge researchers. This is especially true for heterocoupling, that is, oxidative aromatic coupling with the chemoselective formation of a C-C bond between two different arenes. Analysis of the progress achieved in this field since 2013 reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted (cyclo)dehydrogenation, and developing new reagents.

Triple Helical Ir(ppy)3 Phenylene Cage Prepared by Diol-Mediated Benzannulation: Synthesis, Resolution, Absolute Stereochemistry and Photophysical Properties

Cyclometalation of a triple helical N-doped phenylene cage prepared by ruthenium(0)-catalyzed diol-diene benzannulation delivers a chiral, conformationally constrained Ir(ppy)₃ analogue. Like the parent complex, fac-Ir(ppy)₃ , the iridium-containing PAH-cage is phosphorescent, but displays enhanced resistance to oxygen quenching.