Towards the rational design of novel charge-transfer materials: biaryls with a dihedral angle-independent hole delocalization mechanism.

Biaryl cation radicals are important electroactive materials, which show two mechanisms of hole delocalization: static delocalization at small interplanar dihedral angles and dynamic hopping at larger angles, reflecting the interplay between electronic coupling and structural reorganization. Herein, we describe the rational design of biaryls possessing an invariant hole delocalization mechanism.

From Intramolecular (Circular) in an Isolated Molecule to Intermolecular Hole Delocalization in a Two-Dimensional Solid-State Assembly: The Case of Pillarene.

To achieve long-range charge transport/separation and, in turn, bolster the efficiency of modern photovoltaic devices, new molecular scaffolds are needed that can self-assemble in two-dimensional (2D) arrays while maintaining both intra- and intermolecular electronic coupling. In an isolated molecule of pillarene, a single hole delocalizes intramolecularly via hopping amongst the circularly arrayed hydroquinone ether rings. The crystallization of pillarene cation radical produces a 2D self-assembly with three intermolecular dimeric (sandwich-like) contacts.

FHBC, a Hexa-peri-hexabenzocoronene-Fluorene Hybrid: A Platform for Highly Soluble, Easily Functionalizable HBCs with an Expanded Graphitic Core.

Materials based upon hexa-peri-hexabenzocoronenes (HBCs) show significant promise in a variety of photovoltaic applications. There remains the need, however, for a soluble, versatile, HBC-based platform, which can be tailored by incorporation of electroactive groups or groups that can prompt self-assembly. The synthesis of a HBC-fluorene hybrid is presented that contains an expanded graphitic core that is highly soluble, resists aggregation, and can be readily functionalized at its vertices.

Dihedral-Angle-Controlled Crossover from Static Hole Delocalization to Dynamic Hopping in Biaryl Cation Radicals.

In cases of coherent charge-transfer mechanism in biaryl compounds the rates follow a squared cosine trend with varying dihedral angle. Herein we demonstrate using a series of biaryl cation radicals with varying dihedral angles that the hole stabilization shows two different regimes where the mechanism of the hole stabilization switches over from (static) delocalization over both aryl rings to (dynamic) hopping. The experimental data and DFT calculations of biaryls with different dihedral angles unequivocally support that a crossover from delocalization to hopping occurs at a unique dihedral angle where the electronic coupling (H ) is one half of reorganization (λ), that is, H =λ/2.

Deconstructing HPMCAS: Excipient Design to Tailor Polymer-Drug Interactions for Oral Drug Delivery.

Spray-dried dispersions (SDDs) are fascinating polymer-drug mixtures that exploit the amorphous state of a drug to dramatically elevate its apparent aqueous solubility above equilibrium. For practical usage in oral delivery, understanding how polymers mechanistically provide physical stability during storage and prevent supersaturated drugs from succumbing to precipitation during dissolution remains a formidable challenge. To this end, we developed a versatile polymeric platform with functional groups analogous to hydroxypropyl methyl cellulose acetate succinate (HPMCAS, a heterogeneous leading excipient candidate for SDDs) and studied its interactions with Biopharmaceutical Classification System Class II drug models probucol, danazol, and phenytoin at various dosages.

The HOMO Nodal Arrangement in Polychromophoric Molecules and Assemblies Controls the Interchromophoric Electronic Coupling.

Triptycenes spontaneously assemble into two-dimensional networks in which long-range charge transport is facilitated by the extensive electronic coupling through the triptycene framework (intramolecularly) and by cofacial π-stacking (intermolecularly). While designing and synthesizing next-generation triptycenes containing polyaromatic chromophores, the electronic coupling amongst the chromophores was observed to be highly dependent on the nature and position of the substituents. Herein, we demonstrate using hexaalkoxytriptycenes that the electronic coupling amongst the chromophores is switched on and off by a simple repositioning of the substituents, which alters the nodal arrangement of the HOMOs of the individual chromophores.

Precise Compositional Control and Systematic Preparation of Multimonomeric Statistical Copolymers.

A comprehensive approach to target exact molecular weights and chemical compositions for multimonomeric statistical copolymers using a new controlled statistics method with reversible addition-fragmentation chain transfer free-radical (RAFT) polymerization is presented. The system chosen to illustrate this procedure is an acrylic quarterpolymer consisting of methyl acrylate, 2-carboxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-propylacetyl acrylate, modeling a well-known macromolecule utilized to deliver poorly water-soluble drugs (hydroxypropyl methylcellulose acetate succinate, HPMCAS). The relative reactivities at 70 °C between monomer pairs were measured and employed to predict the feed ratio necessary for synthesizing well-defined compositions based on the Walling-Briggs model.

Charge delocalization in self-assembled mixed-valence aromatic cation radicals.

The spontaneous assembly of aromatic cation radicals (D(+•)) with their neutral counterpart (D) affords dimer cation radicals (D(2)(+•)). The intermolecular dimeric cation radicals are readily characterized by the appearance of an intervalence charge-resonance transition in the NIR region of their electronic spectra and by ESR spectroscopy. The X-ray crystal structure analysis and DFT calculations of a representative dimer cation radical (i.

Sequential oxidative transformation of tetraarylethylenes to 9,10-diarylphenanthrenes and dibenzo[g,p]chrysenes using DDQ as an oxidant.

Tetraarylethylenes can be sequentially transformed into 9,10-diarylphenanthrenes and dibenzo[g,p]chrysenes using 1 and 2 equiv of DDQ, respectively, in CH(2)Cl(2) containing methanesulfonic acid, in excellent yields. Efficient access to substituted dibenzochrysenes from tetraarylethylenes establishes the versatility of this procedure over the existing multistep syntheses of dibenzochrysenes. Moreover, the ready regeneration of DDQ from easily recovered reduced DDQ-H(2) continues to advance the use of DDQ/H(+) for the oxidative C-C bond forming reactions.

X-ray structural characterization of charge delocalization onto the three equivalent benzenoid rings in hexamethoxytriptycene cation radical.

Definitive X-ray crystallographic evidence is obtained for a single hole (or a polaron) to be uniformly distributed on the three equivalent 1,2-dimethoxybenzenoid (or veratrole) rings in the hexamethoxytriptycene cation radical. This conclusion is further supported by electrochemical analysis and by the observation of an intense near-IR transition in its electronic spectrum, as well as by comparison of the spectral and electrochemical characteristics with the model compounds containing one and two dimethoxybenzene rings.

Octamethoxydibenzochrysene: isolation and X-ray crystallographic characterization of a twisted polyaromatic cation radical.

The isolation and X-ray crystal structure determination of octamethoxydibenzochrysene () cation radical together with DFT calculations allow us to delineate evidence that the complex structural changes (i.e. elongation and shortening of various bonds) in a polyaromatic hydrocarbon can be predicted based on the positioning of the largest bonding and antibonding character of the HOMO.