Synthesis and electronic properties of nitrogen-rich nanographene

A polycyclic aromatic hydrocarbon displaying twelve edge nitrogen centers for a 42 π-electron system is reported. This compound was synthesized via Sonogashira coupling of pyrimidine precursors, [2+2+2] cycloaddition of bis(aryl) alkynes, and anionic cyclodehydrogenation. Spectroscopy, electrochemistry, and computational results suggest a narrowing of the HOMO-LUMO gap compared to the N-free analogue. Metal coordination affects the optical properties of the extended π system.

Solvent-tunable exciton-charge transfer mixed state enhances emission of functionalized benzo[rst]pentaphene through symmetry breaking

A benzo[rst]pentaphene (BPP) substituted by two bis(methoxyphenyl)amino (MeOPA) groups (BPP-MeOPA) was synthesized and clearly characterized by NMR and single-crystal X-ray analysis. Detailed investigations of its photophysical properties, including transient absorption spectroscopy analyses, revealed that the introduction of the MeOPA groups breaks the symmetry of the BPP core, improving its absorption and emission from an S₁ state with both excitonic and charge-transfer character.

Fluorescent Benzothiadiazole Derivatives as Fluorescence Imaging Dyes: A Decade of New Generation Probes

The current review describes advances in the use of fluorescent 2,1,3-benzothiadiazole (BTD) derivatives after nearly one decade since the first description of bioimaging experiments using this class of fluorogenic dyes. The review describes the use of BTD-containing fluorophores applied as, inter alia, bioprobes for imaging cell nuclei, mitochondria, lipid droplets, sensors, markers for proteins and related events, biological processes and activities, lysosomes, plasma membranes, multicellular models, and animals. A number of physicochemical and photophysical properties commonly observed for BTD fluorogenic structures are also described.

Synthesis and Properties of Conjugated Polymers Based on a Ladderized Anthanthrene Unit

Polycyclic aromatic hydrocarbons (PAHs) are interesting building blocks for the preparation of conjugated polymers due to their extended π surface and planar conformation. However, their use as comonomer in conjugated polymers often leads to nonplanar main chains as a consequence of high steric hindrance at the linking point. Herein, we report the synthesis of a ladderized anthanthrene unit using an sp3 carbon bridge. Three conjugated copolymers with fluorene, isoindigo, and bithiophene derivatives have been synthesized and characterized to study the effect of such ladderization on the electronic properties. The dihedral angle between the ladderized anthanthrene and adjacent units has been significantly reduced by the formation of the sp3 carbon bridge, thus eliminating the steric hindrance with the proton at the peri position of the anthanthrene unit and red-shifting the absorption spectrum by 25 nm.

Regioselective Bromination and Functionalization of Dibenzo[hi,st]ovalene as Highly Luminescent Nanographene with Zigzag Edges

Dibenzo[hi,st]ovalene (DBOV) is a nanographene with a combination of zigzag and armchair edges, consisting of 38 sp² carbons. Excellent optical properties with strong red emission have been demonstrated. Here we report the regioselective bromination of DBOV bearing two mesityl groups (DBOV-Mes) by treatment with N-bromosuccinimide (NBS) under mild conditions. The dibrominated DBOV was further subjected to transition-metal-catalyzed cross-coupling reactions, that is, Suzuki and Sonogashira coupling, demonstrating the edge-decoration of DBOV with different functional groups. Notably, DBOVs arylated at the bay regions showed intense red emission and enhanced fluorescence quantum yields of up to 0.97. Amphoteric reduction and oxidation behavior were observed by cyclic voltammetry (CV) measurements. Chemical oxidation to stable radical cation species was also demonstrated, followed by reduction back to their neutral species.

Probing functional self-assembled molecular architectures with solution/solid scanning tunnelling microscopy

Over the past two decades, solution/solid STM has made clear contributions to our fundamental understanding of the thermodynamic and kinetic processes that occur in molecular self-assembly at surfaces. As the field matures, we provide an overview of how solution/solid STM is emerging as a tool to elucidate and guide the use of self-assembled molecular systems in practical applications, focusing on small molecule device engineering, molecular recognition and sensing and electronic modification of 2D materials.

Hydrogen-Bonded Donor-Acceptor Arrays at the Solution-Graphite Interface

Controlling the nanoscale morphology of organic thin films represents a critical challenge in the fabrication of organic (opto)electronic devices. The morphology of the (multicomponent) thin films in turn depends on the mutual orientation of the molecular components and their supramolecular packing on the surface. Here, it is shown how the surface co-assembly of electron-donating and -accepting building blocks can be controlled via (supra)molecular design. Hexa-peri-hexabenzocoronene (HBC) derivatives with multiple hydrogen-bonding (H-bonding) sites were synthesized and their co-assembly with alkyl-substituted perylene tetracarboxy diimide (PDI) was studied using scanning tunneling microscopy (STM) at the solution-graphite interface. STM data shows that electron-rich HBCs co-assemble laterally with electron deficient PDIs via preprogrammed H-bonding sites with high fidelity. The surface stoichiometry of the two components could be readily tuned by changing the number of H-bonding sites on the HBC derivatives via organic synthesis. This model study highlights the utility of (supra)molecular design in co-assembly of building blocks relevant for organic electronics.