Graphite, the most stable form of elemental carbon, consists of pure carbon sheets stacked upon one another like reams of paper. Individual sheets, known as graphene, prefer planar geometries as a consequence of the hexagonal honeycomb-like arrangements of trigonal carbon atoms that comprise their two-dimensional networks. Defects in the form of non-hexagonal rings in such networks cause distortions away from planarity. Herein we report an extreme example of this phenomenon. A 26-ring C80H30 nanographene that incorporates five seven-membered rings and one five-membered ring embedded in a hexagonal lattice was synthesized by stepwise chemical methods, isolated, purified and fully characterized spectroscopically. Its grossly warped structure was revealed by single-crystal X-ray crystallography. An independent synthetic route to a freely soluble derivative of this new type of 'nanocarbon' is also reported. Experimental data reveal how the properties of such a large graphene subunit are affected by multiple odd-membered-ring defects.

Donor-acceptor triptycences, TPA-QNX(CN)2 and TPA-PRZ(CN)2 were synthesized and their emissive properties were studied. They exhibited a blue-green fluorescence with emission lifetimes on the order of a microsecond in cyclohexane at room temperature. The long lifetime emission is quenched by O 2 and is attributed to thermally activated delayed florescence (TADF). Unimolecular TADF is made possible by the separation and weak coupling due to homo-conjugation of the HOMO and LUMO on different arms of the three-dimensional donoracceptor triptycene. Organic light emitting devices (OLEDs) were fabricated using TPA-QNX(CN)2 and TPA-PRZ(CN)2 as emitters which displayed electroluminescence with efficiencies as high as 9.4% EQE.Since the first report by Tang and Van Slyke in 1987 1 , multi-layered organic light emitting diodes (OLEDs) have attracted interest for utilization in high efficiency illumination and flexible displays.2 OLEDs using fluorescent materials 3 have low internal quantum efficiencies (IQEs) of ≈ 25%, 4 due in part to the inherent limitation of electrical excitation, which generates singlets and triplets in a 1:3 ratio. 5High quantum yield OLEDs with Ir or Pt phosphorescent materials have been intensely investigated for the last several decades 5,6 and now achieve 100% IQE. 5aAlthough phosphorescent materials have defined the present state of OLED technology, there are significant issues including cost, stability of blue emitters, and strong triplet-triplet annihilation at high current density.7 As a result of recent efficiency increases, thermally activated delayed fluorescence (TADF) has become a viable alternative for harvesting both singlet and triplet state in OLEDs. 8,9 TADF is based on reversible intersystem crossing from thermally equilibrated triplet and singlet excited states, and competitive luminescence from the singlet states. If non-radiative pathways are negligible then TADF can achieve 100% electroluminescence IQE. 9f An advantage of TADF materials is that they can be purely organic materials and do not Typical TADF designs employ an electron donor and electron acceptor, which are connected directly but have a twisted geometry ( Figure 1a) to minimize the HOMO-LUMO overlap. 9,13An alternative approach is a through-space interaction wherein electronic systems are in communication by homo-conjugation 14 but are sufficiently separated to create a small singlet-triplet ∆E ST (Figure 1b). The design we report herein places the donor and acceptor on the different fins of a triptycene scaffold. These structures display homoconjugation and many triptycene derivatives display intrinsically high thermal stability, which is critical to OLED manufacturing and opperation. We designed the donor-acceptor triptycences, TPA-QNX(CN)2 and TPA-PRZ(CN)2, as novel TADF materials ( Figure 1c). The triphenylamine functions as the donor and dicyanoquinoxaline or dicyanopyrazine as the acceptor. Our designs were guided by time-dependent density functional theory (TD-DFT) calculations, which prov...

The optoelectronic nature of two-dimensional sheets of sp2-hydridized carbons (for example, graphenes and nanographenes) can be dramatically altered and tuned by altering the degree of π-extension, shape, width and edge topology. Among various approaches to synthesize nanographenes with atom-by-atom precision, one-shot annulative π-extension (APEX) reactions of polycyclic aromatic hydrocarbons hold significant potential not only to achieve a ‘growth from template’ synthesis of nanographenes, but also to fine-tune the properties of nanographenes. Here we describe one-shot APEX reactions that occur at the K-region (convex armchair edge) of polycyclic aromatic hydrocarbons by the Pd(CH3CN)4(SbF6)2/o-chloranil catalytic system with silicon-bridged aromatics as π-extending agents. Density functional theory calculations suggest that the complete K-region selectivity stems from the olefinic (decreased aromatic) character of the K-region. The protocol is applicable to multiple APEX and sequential APEX reactions, to construct various nanographene structures in a rapid and programmable manner.

We have discovered that the combination of Pd(OAc)(2)/o-chloranil can catalyze the direct C-H bond arylation of polycyclic aromatic hydrocarbons (PAHs) with arylboroxins that occurs selectively at the K-region. The sequential integration of Pd-catalyzed direct arylation of PAHs and FeCl(3)-mediated cyclodehydrogenation is effective in rapidly extending a parent PAH π-system with high directionality.

All 10 C-H positions on the rim of corannulene can be arylated by repetitive palladium-catalyzed C-H activation. To relieve congestion among the 10 tightly packed aryl substituents in the product, the central corannulene adopts a nearly planar geometry.