Maxwell J. Robb

Power Factor Enhancement in Solution‐Processed Organic n‐Type Thermoelectrics Through Molecular Design

A new class of high-performance n-type organic thermoelectric materials, self-doping perylene diimide derivatives with modified side chains, is reported. These materials achieve the highest n-type thermoelectric performance of solution-processed organic materials reported to date, with power factors as high as 1.4 μW/mK(2). These results demonstrate that molecular design is a promising strategy for enhancing organic thermoelectric performance.

Fabrication of Unique Chemical Patterns and Concentration Gradients with Visible Light

A modular and general method based on a photomediated ATRA reaction for the spatially controlled functionalization of surfaces with visible light is reported. The ability to control reactivity with light intensity combined with the orthogonality of ATRA chemistry allows well-defined chemically differentiated monolayers and complex nonlinear chemical concentration gradients to be easily prepared. Use of light to mediate these reactions permits spatial regulation and the generation of unique, multifunctional chemical gradients.

Synthetic Aptamer-Polymer Hybrid Constructs for Programmed Drug Delivery into Specific Target Cells

Viruses have evolved specialized mechanisms to efficiently transport nucleic acids and other biomolecules into specific host cells. They achieve this by performing a coordinated series of complex functions, resulting in delivery that is far more efficient than existing synthetic delivery mechanisms. Inspired by these natural systems, we describe a process for synthesizing chemically defined molecular constructs that likewise achieve targeted delivery through a series of coordinated functions. We employ an efficient “click chemistry” technique to synthesize aptamer-polymer hybrids (APHs), coupling cell-targeting aptamers to block copolymers that secure a therapeutic payload in an inactive state. Upon recognizing the targeted cell-surface marker, the APH enters the host cell via endocytosis, at which point the payload is triggered to be released into the cytoplasm. After visualizing this process with coumarin dye, we demonstrate targeted killing of tumor cells with doxorubicin. Importantly, this process can be generalized to yield APHs that specifically target different surface markers.

25th anniversary article: no assembly required: recent advances in fully conjugated block copolymers.

Fully conjugated block copolymers have emerged as promising materials that combine semiconducting properties with the ability to self-assemble at the nanoscale. The convergence of these two features has tremendous implications for a number of fundamental molecular assembly and transport questions, while also offering unique advantages for a variety of applications. For example, a nanostructured active layer in organic photovoltaic (OPV) devices may provide for efficient charge separation while simultaneously affording continuous, unimpeded pathways for charge carriers to migrate to their respective electrodes within each individual microphase. This review details the recent progress made in the preparation and application of fully conjugated block copolymers and serves as a comprehensive reference for the materials that have been reported in the literature to date. Focus is placed on fully conjugated block copolymers prepared using chemistries that are relevant to high-performance polymers in organic electronics research, for example Stille, Suzuki-Miyaura, and Yamamoto coupling.

De Novo Design of Bioactive Protein-Resembling Nanospheres via Dendrimer-Templated Peptide Amphiphile Assembly

Self-assembling peptide amphiphiles (PAs) have been extensively used in the development of novel biomaterials. Because of their propensity to form cylindrical micelles, their use is limited in applications where small spherical micelles are desired. Here we present a platform method for controlling the self-assembly of biofunctional PAs into spherical 50 nm particles using dendrimers as shape-directing scaffolds. This templating approach results in biocompatible, stable protein-like assemblies displaying peptides with native secondary structure and biofunctionality.

Polymers with autonomous life-cycle control

The lifetime of man-made materials is controlled largely by the wear and tear of everyday use, environmental stress and unexpected damage, which ultimately lead to failure and disposal. Smart materials that mimic the ability of living systems to autonomously protect, report, heal and even regenerate in response to damage could increase the lifetime, safety and sustainability of many manufactured items. There are several approaches to achieving these functions using polymer-based materials, but making them work in highly variable, real-world situations is proving challenging.

A Robust Damage-Reporting Strategy for Polymeric Materials Enabled by Aggregation-Induced Emission

Microscopic damage inevitably leads to failure in polymers and composite materials, but it is difficult to detect without the aid of specialized equipment. The ability to enhance the detection of small-scale damage prior to catastrophic material failure is important for improving the safety and reliability of critical engineering components, while simultaneously reducing life cycle costs associated with regular maintenance and inspection. Here, we demonstrate a simple, robust, and sensitive fluorescence-based approach for autonomous detection of damage in polymeric materials and composites enabled by aggregation-induced emission (AIE). This simple, yet powerful system relies on a single active component, and the general mechanism delivers outstanding performance in a wide variety of materials with diverse chemical and mechanical properties.

Modulating structure and properties in organic chromophores: influence of azulene as a building block

The properties of isomeric azulene derivatives, substituted through the 5-membered ring, were examined using a combination of experimentation and theoretical calculations for a series of well-defined electroactive oligomers. The substitution pattern was shown to dramatically influence solid-state, electronic, and optical properties of the oligomers with acid-responsive materials only being observed when the azulenium cation could be directly stabilized by substituents on the 5-membered ring. In addition, the absorption maxima and optical band-gaps of the azulenium cations can be tuned by the substitution position of the azulene ring by the chromophore.

A Retro-Staudinger Cycloaddition: Mechanochemical Cycloelimination of a β-Lactam Mechanophore.

Mechanical activation of a β-lactam mechanophore using ultrasound induces a formal [2 + 2] cycloelimination reaction producing ketene and imine functional groups--the reverse reaction of the Staudinger cycloaddition. This transformation is predicted by computational modeling and verified by kinetics and UV-vis absorption measurements as well as polymer end-group analysis using (1)H and (13)C NMR spectroscopy. Addition of the β-lactam motif to the current repertoire of covalent mechanophores coupled with the diverse reactivity of the ketene functional group provides a promising new platform for achieving materials capable of autonomic self-healing behavior in response to external forces.

Regioisomer-Specific Mechanochromism of Naphthopyran in Polymeric Materials

Transformation of naphthopyran into a colored merocyanine species in polymeric materials is achieved using mechanical force. We demonstrate that the mechanochemical reactivity of naphthopyran is critically dependent on the regiochemistry, with only one particular substitution pattern leading to successful mechanochemical activation. Two alternative regioisomers with different polymer attachment points are demonstrated to be mechanochemically inactive. This trend in reactivity is accurately predicted by DFT calculations, reinforcing predictive capabilities in mechanochemical systems. We rationalize the reactivity differences between naphthopyran regioisomers in terms of the alignment of the target C-O pyran bond with the direction of the applied mechanical force and its effect on mechanochemical transduction along the reaction coordinate.