We report a computational study of mesoscale morphology and charge-transport properties of radially π-conjugated cycloparaphenylenes ([n]CPPs) of various ring sizes (n = 5−12, where n is the number of repeating phenyl units). These molecules are considered structural constituents of fullerenes and carbon nanotubes.[n]CPP molecules are nested in a unique fashion in the solid state. Molecular dynamics simulations show that while intramolecular structural stability (order) increases with system size, intermolecular structural stability decreases. Density functional calculations reveal that reorganization energy, an important parameter in charge transfer, decreases as n is increased. Intermolecular charge-transfer electronic couplings in the solid state are relatively weak (due to curved π-conjugation and loose intermolecular contacts) and are on the same order of magnitude (∼10 meV) for each system. Intrinsic charge-carrier mobilities were simulated from kinetic Monte Carlo simulations; hole mobilities increased with system size and scaled as ∼n 4 . We predict that disordered [n]CPPs exhibit hole mobilities as high as 2 cm 2 /(V•s). Our computations show a strong correlation between reorganization energy and hole mobility (μ ∼ λ −4 ). Quantum mechanical calculations were performed on cofacially stacked molecular pairs for varying phenyl units and reveal that orbital delocalization is responsible for both decreasing reorganization energies and electronic couplings as n is increased.

We demonstrate a highly efficient thermal conversion of four differently substituted polydiacetylenes (PDAs 1 and 2a-c) into virtually indistinguishable N = 8 armchair graphene nanoribbons ([8]GNR). PDAs 1 and 2a-c are themselves easily accessed through photochemically initiated topochemical polymerization of diynes 3 and 4a-c in the crystal. The clean, quantitative transformation of PDAs 1 and 2a-c into [8]GNR occurs via a series of Hopf pericyclic reactions, followed by aromatization reactions of the annulated polycyclic aromatic intermediates, as well as homolytic bond fragmentation of the edge functional groups upon heating up to 600 °C under an inert atmosphere. We characterize the different steps of both processes using complementary spectroscopic techniques (CP/MAS C NMR, Raman, FT-IR, and XPS) and high-resolution transmission electron microscopy (HRTEM). This novel approach to GNRs exploits the power of crystal engineering and solid-state reactions by targeting very large organic structures through programmed chemical transformations. It also affords the first reported [8]GNR, which can now be synthesized on a large scale via two operationally simple and discrete solid-state processes.

In order to understand the conformational behavior of organic components in organic electronic devices, we have computed the torsional potentials for a library of thiophene-based heterodimers. The accuracy and efficiencies of computational methods for these organic materials were benchmarked for 11 common density functionals with three Pople basis sets against a Focal Point Analysis (FPA) on a model oligothiophene 2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]-thiophene (BTTT) system. This study establishes a set of general trends in regards to conformational preferences, as well as planarization and rotational barriers for a library comprised of common fragments found in organic materials. These gas phase structures are compared to experimental crystal structures to determine the effect of crystal packing on geometry. Finally, we analyze the structure of hole-transporting material DERDTS-TBDT and design a new oligomer likely to be planar in the solid state.

Expanded helicenes are large, structurally flexible π-frameworks that can be viewed as building blocks for more complex chiral nanocarbons. Here we report a gram-scale synthesis of an alkyne-functionalized expanded [11]­helicene and its single-step transformation into two structurally and functionally distinct types of macrocyclic derivatives: (1) a figure-eight dimer via alkyne metathesis (also gram scale) and (2) two arylene-bridged expanded helicenes via Zr-mediated, formal [2+2+n] cycloadditions. The phenylene-bridged helicene displays a substantially higher enantiomerization barrier (22.1 kcal/mol) than its helicene precursor (<11.9 kcal/mol), which makes this a promising strategy to access configurationally stable expanded helicenes. In contrast, the topologically distinct figure-eight retains the configurational lability of the helicene precursor. Despite its lability in solution, this compound forms homochiral single crystals. Here, the configuration is stabilized by an intricate network of two distinct yet interconnected helical superstructures. The enantiomerization mechanisms for all new compounds were probed using density functional theory, providing insight into the flexibility of the figure-eight and guidance for future synthetic modifications in pursuit of non-racemic macrocycles.

We report the design and synthesis of a new class of indole-based conjugated trimers. The targeted compounds are accessed from in situ generated, highly reactive indolyne intermediates using Pd-catalyzed cyclotrimerization reactions. By harnessing three indolyne isomers, six isomeric indole trimers are accessible, none of which have been previously synthesized. Using computational analysis, we describe the structural and photophysical properties of these unique compounds. This study showcases the use of indolynes in transition metal-catalyzed reactions, while providing access to a new class of conjugated trimers, including highly bent heteroaromatic compounds. Computations indicate that, despite differences in planarity between the molecules, the photophysical properties of each trimer are derived from the N-methylindole building block. Excited state behavior follows predicable patterns.