Emerging C H functionalization strategies for constructing fused polycyclic aromatic hydrocarbons and nanographenes

Curved Nanographenes: Multiple Emission, Thermally Activated Delayed Fluorescence, and Non-Radiative Decay

The intriguing and rich photophysical properties of three curved nanographenes (CNG 6, 7, and 8) are investigated by time-resolved and temperature-dependent photoluminescence (PL) spectroscopy. CNG 7 and 8 exhibit dual fluorescence, as well as dual phosphorescence at low temperature in the main PL bands. In addition, hot bands are detected in fluorescence as well as phosphorescence, and, in the narrow temperature range of 100-140 K, thermally activated delayed fluorescence (TADF) with lifetimes on the millisecond time-scale is observed. These findings are rationalized by quantum-chemical simulations, which predict a single minimum of the S1 potential of CNG 6, but two S1 minima for CNG 7 and CNG 8, with considerable geometric reorganization between them, in agreement with the experimental findings. Additionally, a higher-lying S2 minimum close to S1 is optimized for the three CNG, from where emission is also possible due to thermal activation and, hence, non-Kasha behavior. The presence of higher-lying dark triplet states close to the S1 minima provides mechanistic evidence for the TADF phenomena observed. Non-radiative decay of the T1 state appears to be thermally activated with activation energies of roughly 100 meV and leads to disappearance of phosphorescence and TADF at T > 140 K.

Palladium-catalyzed annulative π-extension of o-halobiphenyls with o-chloropyridinecarboxylic acids to access azatriphenylenes

A palladium-catalyzed bay-region annulative π-extension reaction of o-halobiphenyls with o-chloropyridinecarboxylic acids was developed. A variety of azatriphenylene derivatives could be synthesized by this approach.

Palladium-Catalyzed Sequential Vinyl C-H Activation/Dual Decarboxylation: Regioselective Synthesis of Phenanthrenes and Cyclohepta[1,2,3-de]naphthalenes

The application of a C(vinyl), C(aryl)-palladacycle from vinyl-containing substrates is challenging due to the interference of a reactive double bond in palladium catalysis. This Letter describes a [4 + 2] or [4 + 3] cyclization based on a C(vinyl), C(aryl)-palladacycle by employing α-oxocarboxylic acids as the insertion units under a palladium/air system. The reaction proceeded through the key vinyl C-H activation and dual decarboxylation sequence, forming phenanthrenes and cyclohepta[1,2,3-de]naphthalenes regioselectively in good yields. The synthetic versatility of this protocol is highlighted by the gram-scale synthesis and synthesizing functional material molecule.

Late-Stage Functionalisation of Polycyclic (N-Hetero-) Aromatic Hydrocarbons by Detoxifying CYP5035S7 Monooxygenase of the White-Rot Fungus Polyporus arcularius

Functionalisation of polycyclic aromatic hydrocarbons (PAHs) and their N-heteroarene analogues (NPAHs) is a tedious synthetic endeavour that requires diverse bottom-up approaches. Cytochrome P450 enzymes of white-rot fungi were shown to participate in the fungal detoxification of xenobiotics and environmental hazards via hydroxylation of PAH compounds. In this paper, the recently discovered activity of the monooxygenase CYP5035S7 towards (N)PAHs was investigated in detail, and products formed from the substrates azulene, acenaphthene, fluorene, anthracene, and phenanthrene by whole-cell biocatalysis were isolated and characterised. The observed regioselectivity of CYP5035S7 could be explained by a combination of the substrate's electron density and steric factors influencing the substrate orientation giving insight into the active-site geometry of the enzyme.

Novel Synthetic Approach to Heteroatom Doped Polycyclic Aromatic Hydrocarbons: Optimizing the Bottom-Up Approach to Atomically Precise Doped Nanographenes

The success of the rational bottom-up approach to nanostructured carbon materials and the discovery of the importance of their doping with heteroatoms puts under the spotlight all synthetic organic approaches to polycyclic aromatic hydrocarbons. The construction of atomically precise heteroatom doped nanographenes has evidenced the importance of controlling its geometry and the position of the doping heteroatoms, since these parameters influence their chemical-physical properties and their applications. The growing interest towards this research topic is testified by the large number of works published in this area, which have transformed a once "fundamental research" into applied research at the cutting edge of technology. This review analyzes the most recent synthetic approaches to this class of compounds.

Bay-Region Annulative π-Extension of o-Iodobiphenyls with Aliphatic Anhydrides Catalyzed by Pd(OAc)2

Bay-region annulative π-extension of o-iodobiphenyls with aliphatic anhydrides was developed. Many o-iodobiphenyls and aliphatic anhydrides can react well under the optimized conditions. A lot of phenanthrol derivatives can be efficiently prepared by this approach. The control experiments support that dibenzopalladacyclopentadienes may be the reaction intermediates.

Rules of Nucleophilic Additions to Zigzag Nanographene Diones*

Nucleophilic addition of carbon-centered nucleophiles to nanographene ketones represents a valuable late-stage method for the functionalization of zigzag nanographenes, but its use is rare in the chemical literature. Using two model systems, non-Kekulé triangulene-4,8-dione and Kekulé anthanthrone, we identify unexpected regioselectivities and uncover the rules that govern these reactions. Considering the large number of nanographene ketones that have been reported since the pioneering work of Eric Clar, this method enables synthesis and exploration of hitherto unknown functionalized nanographenes.

Exploration of Kobayashi's aryne precursor: a potent reactive platform for the synthesis of polycyclic aromatic hydrocarbons

Arynes due to their transient nature leads to remarkable and versatile applications in the synthetic world. Apparently, researchers have focused on the construction of simple to complex π-conjugated systems using arynes as the reactive platform. In this regard, Kobayashi's aryne precursor has shown a great extent of reactivity and afforded significant advancement in the synthesis of polycyclic aromatic systems with wide practical utility. This review emphasizes the extensive utilization of Kobayashi's aryne intermediates and their derivatives for the synthesis of different classes of polycyclic aromatic hydrocarbons (PAHs).