A Twisted Bay-Substituted Quaterrylene Phosphorescing in the NIR Spectral Region

Furan-Extended Helical Rylenes with Fjord Edge Topology and Tunable Optoelectronic Properties

Lateral furan-expansion of polycyclic aromatics, which enables multiple O-doping and peripheral edge evolution of rylenes, is developed for the first time. Tetrafuranylperylene TPF-4CN and octafuranylquaterrylene OFQ-8CN were prepared as model compounds bearing unique fjord edge topology and helical conformations. Compared to TPF-4CN, the higher congener OFQ-8CN displays a largely red-shifted (≈333 nm) and intensified absorption band (λ_max =829 nm) as well as a narrowed electrochemical band gap (≈1.08 eV) due to its pronounced π-delocalization and emerging of open-shell diradicaloid upon the increase of fjord edge length. Moreover, strong circular dichroism signals in a broad range until 900 nm are observed for open-shell chiral OFQ-8CN, owing to the excellent conformational stability of its central bis(tetraoxa[5]helicene) fragments. Our studies provide insights into the relationships between edge topologies and (chir)optoelectronic properties for this novel type of O-doped PAHs.

Helically Twisted Nanoribbons Based on Emissive Near-Infrared Responsive Quaterrylene Bisimides

Graphene nanoribbons (GNRs) have the potential for next-generation functional devices. So far, GNRs with defined stereochemistry are rarely reported in literature and their optical response is usually bound to the ultraviolet or visible spectral region, while covering the near-infrared (NIR) regime is still challenging. Herein, we report two novel quaterrylene bisimides with either one- or twofold-twisted π-backbones enabled by the steric congestion of a fourfold bay arylation leading to an end-to-end twist of up to 76°. The strong interlocking effect of the π-stacked aryl substituents introduces a rigidification of the chromophore unambiguously proven by single-crystal X-ray analysis. This leads to unexpectedly strong NIR emissions at 862 and 903 nm with quantum yields of 1.5 and 0.9%, respectively, further ensuring high solubility as well as resolvable and highly stable atropo-enantiomers. Circular dichroism spectroscopy of these enantiopure chiral compounds reveals a strong Cotton effect Δε of up to 67 M^-1 cm^-1 centered far in the NIR region at 849 nm.

Exciton Delocalization Counteracts the Energy Gap: A New Pathway toward NIR-Emissive Dyes

Exciton coupling between the transition dipole moments of ordered dyes in supramolecular assemblies, so-called J/H-aggregates, leads to shifted electronic transitions. This can lower the excited state energy, allowing for emission well into the near-infrared regime. However, as we show here, it is not only the excited state energy modifications that J-aggregates can provide. A bay-alkylated quaterrylene was synthesized, which was found to form J-aggregates in 1,1,2,2-tetrachloroethane. A combination of superradiance and a decreased nonradiative relaxation rate made the J-aggregate four times more emissive than the monomeric counterpart. A reduced nonradiative relaxation rate is a nonintuitive consequence following the 180 nm (3300 cm^-1) red-shift of the J-aggregate in comparison to the monomeric absorption. However, the energy gap law, which is commonly invoked to rationalize increased nonradiative relaxation rates with increasing emission wavelength, also contains a reorganization energy term. The reorganization energy is highly suppressed in J-aggregates due to exciton delocalization, and the framework of the energy gap law could therefore reproduce our experimental observations. J-Aggregates can thus circumvent the common belief that lowering the excited state energies results in large nonradiative relaxation rates and are thus a pathway toward highly emissive organic dyes in the NIR regime.

Direct borylation of terrylene and quaterrylene

The preparation of large rylenes often needs the use of solubilizing groups along the rylene backbone, and all the substituents of the terrylenes and quaterrylenes were introduced before creating the rylene skeleton. In this work, we successfully synthesized 2,5,10,13-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)terrylene (TB4) by using an iridium-catalyzed direct borylation of C–H bonds in terrylene in 56% yield. The product is soluble in common organic solvents and could be purified without column chromatography. Single crystal X-ray diffraction analysis revealed that the terrylene core is not disturbed by the substituents and is perfectly flat. The photophysical properties of TB4 are also unchanged by the substituents because the carbon atoms at 2,5,10,13-positions have less coefficients on its HOMO and LUMO, estimated by theoretical calculations. Finally, the same borylation reaction was applied for quaterrylene, resulting in the formation of soluble tetra-borylated quaterrylene despite a low yield. The post modification of rylenes enables us to prepare their borylated products as versatile units after creating the rylene skeletons.